AC/Furnace Questions- 1 stage or 2 stage?

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DVA79
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AC/Furnace Questions- 1 stage or 2 stage?

Post by DVA79 » Sun Feb 25, 2018 3:15 pm

Hi All, I’m currently getting quotes and doing research on new HVAC to replace my current 20 year old set up and was hoping some of you who have been through this process could give me some feedback, especially given the seemingly dizzying amount of options to choose from!

For those of you who have replaced their furnace and AC, I was wondering if you have a 2-stage furnace and if you have had any issues with it? Some contractors say the 2-stage does a great job of evening out temp between 1st and 2nd floors whereas others recommend getting a single stage (95% efficiency) due to problems of not getting enough heat to supply ducts far from the furnace during the low stage.

I currently have an 135,000 BTU, 80% efficient single stage furnace and a 5-ton AC for an approximately 3000 sqft house (no zones) in the Chicagoland area. All the HVAC contractors I have talked to agreed the furnace is likely oversized (although it heats the house just fine). I am, however, getting conflicting advice on if the AC should remain 5-ton or 4-ton. Some recommend 4-ton and argue the smaller unit runs a bit longer but does a better job dehumidifying thus allowing the thermostat temp to go up a bit.

Accordingly, I and am debating between the following options:

Furnace (either Carrier, Heil, or Goodman)
100,000 BTU 2-stage (96%)
100,000 BTU 1-stage (96%)
120,000 BTU (same options above)

AC (same brands as above)
4 ton AC 1-stage
5-ton AC 1-stage

Furnace Questions:
Did you go with 1-stage or 2-stage? Do you like the 2-stage? Does it heat upstairs during low stage? Have you noticed energy savings? How is the sound? If you have similar sq footage, what BTU size furnace did you go with? Some tell me 2-stage furnaces are more prone to breakdown and other say this is untrue—what has your experience been?

AC Questions:
If you have comparable sqft, do you know the size of your AC and are you satisfied with it?

Brand Questions.
Most of what I have read say brand is not as important as a quality install by a reputable contractor. However, still curious if you have had any problems with a specific brand.

Thanks in advance!


Edit:
I added this towards bottom of thread but I probably should have included it in my initial post:

My quotes have been the following:

-Contractor #1: Carrier: Furnace: 120,000 BTU (2- stage 96%), AC: 5 ton (single stage) - $10,800

-Contractor #2: Heil: Furnace: 100,000 BTU (2-stage 96%), AC: 4 ton (single stage) - $8,010 (add $460 for the aprilaire air filter he recommended also installing--not sure if I would do this as I haven't read much on these yet).

-Contractor #3: Goodman: Furnace 100,000 BTU (2-stage 96%), AC: 5 ton (single stage) - $6789 (this contractor works from his house and does not appear as professional as the other, but has been in the business for 25+ years).

What do you all think of these prices?

I have know that Carrier and Heil both have the same parent company and are pretty similar in quality (although Carrier has better branding) -- not sure If the higher cost of Carrier is worth it. May try to get this quote down with a smaller sized equipment.

I have read conflicting things on Goodman. They do appear a bit lower ended and you can buy them online and DIY the job. I suspect that is where much of the quality issue might come from (poor installs).
Last edited by DVA79 on Sun Feb 25, 2018 7:48 pm, edited 1 time in total.

livesoft
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by livesoft » Sun Feb 25, 2018 3:20 pm

We have 3000+ sq ft home in Texas. We have 2 furnaces -- one for each floor. We just replaced one with essentially what we had before. It was a simple drop-in replacement. Single-stage, 80,000 BTU single-stage, 80% efficient, natural gas furnace. No ductwork, no new thermostat, no extras. 3-Ton single-speed air/fan. Just a straight replace of a 23-year-old gas furnace.

We didn't care about efficiency nor stages because our home is well insulated and we just don't have high utility bills. The furnace wasn't even used during the prior 2 years because the heat from the other floor was enough to keep the floor with broken furnace comfortable.

It costs us about $250 a year to heat the house, so energy savings will never amount to more than $250 a year for us and that would be with both furnaces not being used.

Brand was American Standard. You can buy the furnace online if you want and install it yourself. Prices are easy to find.

Cost was $2360 + tax. I would not be surprised to find out that we paid $500 too much. :)
Last edited by livesoft on Sun Feb 25, 2018 3:33 pm, edited 3 times in total.
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by Sandtrap » Sun Feb 25, 2018 3:26 pm

We have a 3 story home. 4500+sf. Each floor has a dedicated AC/Furnace system. All are oversized. It's been a good setup. Monthly utility costs are fairly low. All 1 stage.
j :D

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fortfun
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by fortfun » Sun Feb 25, 2018 3:35 pm

My home is about the same size as yours. I have two things to contribute:

1. I have a simple, inexpensive, single stage, 80% efficient furnace. I've had zero problems with it. My neighbor has a fancy, expensive, 2 stage, 95% efficient furnace. He's had nothing but problems with his. He will never make up the cost of the service calls, despite the efficient unit that he has.

2. My AC is oversized for my house. The HVAC guys told me to get a smaller one that runs all of the time. I'm glad I got the larger one.

You might check into local rebates and see if they will reduce the cost.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by bubbadog » Sun Feb 25, 2018 3:42 pm

I have a 3,000 SF home in the Midwest. I replaced my central air unit 4 years ago with a heat pump version. It is my understanding that the heat pump is cheaper to operate than the natural gas furnace until it gets too cold outside (30-35 degrees?). My existing single stage natural gas furnace then kicks in for colder temps. The heat pump version was about $500 more than a comparable central air unit. Have you explored this option?

DVA79
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by DVA79 » Sun Feb 25, 2018 4:02 pm

bubbadog wrote:
Sun Feb 25, 2018 3:42 pm
I have a 3,000 SF home in the Midwest. I replaced my central air unit 4 years ago with a heat pump version. It is my understanding that the heat pump is cheaper to operate than the natural gas furnace until it gets too cold outside (30-35 degrees?). My existing single stage natural gas furnace then kicks in for colder temps. The heat pump version was about $500 more than a comparable central air unit. Have you explored this option?
Interesting. I don’t know anything about heat pumps—is this part of the AC unit?

Parthenon
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by Parthenon » Sun Feb 25, 2018 4:04 pm

In 2010 I replaced a Carrier furnace with a 2 stage Trane rated at 76,000 Btu. The house is a 2,700 square foot two story located in the western suburbs of Chicago. The original furnace was rated at 110,000 Btu but only 85% or so efficienct and because it constantly short cycled I de-rated it down to 80,000 BTU. Even then it didn't run that long. The installer of the new furnace showed me how to install a switch to only run the second stage when I turned it on. Since 2010 I have never used the second stage. The first stage is rated at 46,000 Btu and has never had a problem keeping the house at 68 degrees, and again doesn't run that long even with temperatures below zero. Granted when I built the house in 1984 I did install additional insulation in the walls but you can only go so far with 2x4 studs.

The only reason I replace the Carrier was because of it's age. I figured after 26 years it might be about time.

Ed
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by sport » Sun Feb 25, 2018 4:12 pm

We replaced a furnace about 20 years ago. We put in a 2 stage. The unit actually had a 3-speed blower. The high speed was used for AC. The two lower speeds were for heating. Most of the time, the furnace ran on the low speed. So, it was quieter and the heat was more even. The second speed only came on if the blower ran for too long, along with additional burners. The control unit in the furnace determined this automatically. The new furnace was an 80% efficient unit and we had lower heating bills than with the old one. However the old one was a 1966 model and I don't know what the efficiency was. I expect the lower bills were due to the higher efficiency, and the 2-stage feature had little to do with it. The new furnace was a Carrier and we had no problems with it during the 10 years we lived there after it was installed. We also included a Carrier humidifier on the furnace which also served us well.

For comparison, our new house has a single stage Carrier furnace installed by the builder. This year, after 11 years, the control unit died. The replacement part cost $495.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by Smorgasbord » Sun Feb 25, 2018 4:16 pm

I'm in Northwest Indiana, right by the lake, with a ~4000 square foot house. Last year, we replaced the AC unit, and I believe we went with a 3.5 ton unit. It works fine. Admittedly, as the weather guys always say, it's "cooler by the lake" but it is often a bit more humid too.

DVA79
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by DVA79 » Sun Feb 25, 2018 4:19 pm

Parthenon wrote:
Sun Feb 25, 2018 4:04 pm
. The first stage is rated at 46,000 Btu and has never had a problem keeping the house at 68 degrees, and again doesn't run that long even with temperatures below zero. Granted when I built the house in 1984 I did install additional insulation in the walls but you can only go so far with 2x4 studs.

Ed
Thanks. So the heat supply reached even far rooms on the 2nd floor with no issues? My biggest concern is that no heat would get upstairs in the first stage. (yes I know heat rises :D but upstairs is ususally cooler in my house if I don’t manipulate dampers on first level).

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by bob60014 » Sun Feb 25, 2018 4:28 pm

2400 Sq ft house in the NW burbs, replaced a 22yoa Trane single stage with a dual stage Carrier. Works great and love it. I noticed on those "tweener" days, not really cold but still a chill in the air or not really a hot day but warm enough to be slightly uncomfortable, this is where it shines. Takes the chill off or cools it down as needed. Along with having a smart tstat the gas and electric bills are down

Be sure to get a A+++++ installer, makes all the difference.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by mortfree » Sun Feb 25, 2018 4:37 pm

I thought two stage kicks in to achieve the set temperature when you are a few degrees away (I.e. going from 64 to 70 for heat). So the output is higher. First stage runs at a lower output than second stage. I would guess that a one stage furnace output would run somewhere in between the two stages.

I had a two stage Trane furnace and a thermostat that came with an app. I rarely saw the two stage show up in the history.

If the unit comes with an ECM motor/fan (I believe that is the term) do realize how expensive they are to replace if they fail.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by Epsilon Delta » Sun Feb 25, 2018 4:43 pm

Most multi stage furnaces have a dip-switch or jumpers to configure how the two stages are used. A good many installers will configure them so it always runs in high (i.e. all stages turn on and off together). It is worth reading the manual, and worth finding an installer who is not stuck in the 80's or whenever it was that multi stage furnaces became available. On the other hand if you get a multi stage and you find you don't like quite, even heat and saving money, you can always disable the low stage to get blasts of searing heat. :twisted:

SpaethCo
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by SpaethCo » Sun Feb 25, 2018 4:44 pm

If you look at the design of 1-stage vs 2-stage, the only real difference is a 2nd gas valve and a 2-speed inducer motor, so that shouldn't matter for reliability. It's not until you get into modulating furnaces with an actuator that adjusts a single gas valve and a full ECM flue exhaust motor where I would start to be concerned about complexity/repairs.

For temperature consistency, maybe consider something like https://www.ecobee.com/ for a thermostat. You can place tiny watch-battery powered temperature/motion sensors around the house so that the stat has more data to use for determining the temperature. Say you had a 4 degree spread between upstairs and downstairs, it will try and split the difference where one floor will be 2 degrees below set point, the other floor will be 2 degrees above set point. You can also have profiles like "sleeping" where it will only take the upstairs temperature probes into consideration.

When it comes to picking brands, I recommend checking on parts availability. We were going to go with Lennox until we asked around and found a lot of places have a days/weeks lead time on many parts. We ended up going with Carrier because the big shops in this area that warehouse parts keep just about everything in stock for Carrier/Bryant.

For 2100sq ft house in Minnesota, we just replaced a builder's original 90,000 BTU 80% efficient furnace with a 60,000 BTU 96% efficient2 2-stage furnace. The biggest surprise is that the 2nd stage only runs when the system recovers from an auto-away/auto-home setback. (The Ecobee won't let the house get colder than what it can recover to set point at stage 2 within 30 minutes) Even on the days where it was -18F, the house had no problem maintaining a 72F set point staying in stage 1.

The thermostat makes a big difference. If you don't get a 2-stage stat, they make the furnace control when the 2nd stage kicks in based on runtime, but it's a ridiculously poor solution. (IMO)

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by Parthenon » Sun Feb 25, 2018 4:48 pm

DVA79 wrote:
Sun Feb 25, 2018 4:19 pm
Parthenon wrote:
Sun Feb 25, 2018 4:04 pm
. The first stage is rated at 46,000 Btu and has never had a problem keeping the house at 68 degrees, and again doesn't run that long even with temperatures below zero. Granted when I built the house in 1984 I did install additional insulation in the walls but you can only go so far with 2x4 studs.

Ed
Thanks. So the heat supply reached even far rooms on the 2nd floor with no issues? My biggest concern is that no heat would get upstairs in the first stage. (yes I know heat rises :D but upstairs is ususally cooler in my house if I don’t manipulate dampers on first level).
Actually, because the house faces the south, the upstairs are warmer than downstairs to the extent that I usually shut off the upstairs registers and rely on the heating effects of the sun through the bedroom windows. This only works on sunny days but in the winter when it gets extremely cold it's usually sunny. Because the DC motor is so efficient, during extremely cold spells, I'll leave the fan run continuously. The installer claimed that if I ran the fan continuously all year long it would only cost $54. That may be but I would take that statement with a grain of salt.

Ed
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by Kenkat » Sun Feb 25, 2018 4:49 pm

mortfree wrote:
Sun Feb 25, 2018 4:37 pm
I thought two stage kicks in to achieve the set temperature when you are a few degrees away (I.e. going from 64 to 70 for heat). So the output is higher. First stage runs at a lower output than second stage. I would guess that a one stage furnace output would run somewhere in between the two stages.
This is how ours works. I typically only hear the second stage when it is bringing the heat up in the morning or very rarely if it is really really cold outside (below zero).

We replaced a builder grade Trane 90% efficiency single stage furnace and 10 seer A/C unit with a Carrier 98% efficiency two stage unit and 14 seer A/C unit about 6 years ago. The new furnace provides much better overall comfort in terms of temperature between rooms and is much quieter than the old unit as well. No problems so far with any of the equipment and I would do a 2 stage unit again if I were repeating the process.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by OnTrack » Sun Feb 25, 2018 5:12 pm

mortfree wrote:
Sun Feb 25, 2018 4:37 pm
If the unit comes with an ECM motor/fan (I believe that is the term) do realize how expensive they are to replace if they fail.
On the other hand, electrically commutated (ECM) variable-speed fan motors use less electricity and the payback period is estimated at 7 years. Also note that AFUE efficiency ratings don't take into account the electricity used by the fan motor.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by Liberty1100 » Sun Feb 25, 2018 5:25 pm

I would like to suggest you get the two-stage 120,000 furnace. With only the first stage running, you should be generating enough heat for the forst floor and it should run long enough to have heat reach the upper level. With a single stage, you are blasting a ton of heat or none at all. For comfort, generally the longer the a/c or furnace runs, the better.

I would be careful comparing other houses with yours. The furnace and AC capacity depends on your climate, the materials your house is made of, indirect/Direct
sunlight, and how your house is constructed (split level vs colonial, retrofitted forced air vs built with forced air). I believe if you are curious, you can get a thermal analysis of your house done by a mechanical engineer, which will give you more specific numbers.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by indexfundfan » Sun Feb 25, 2018 5:41 pm

Epsilon Delta wrote:
Sun Feb 25, 2018 4:43 pm
Most multi stage furnaces have a dip-switch or jumpers to configure how the two stages are used. A good many installers will configure them so it always runs in high (i.e. all stages turn on and off together).
That's my experience when I replaced my HVAC. My old system was only single stage and there was insufficient number of signaling wires to control a second stage. It was only with my insistence that they ran a new wire so that the second stage can be controlled by the thermostat.

If you buy a two-stage system, make sure you put in a two-stage thermostat and have the second stage controlled by the thermostat and not by some delay timer to kick in the second stage within the HVAC unit. Remember, only the thermostat knows the temperature in the room. When the room temperature is far from the set temperature, the thermostat can kick in high heat sooner.
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killjoy2012
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by killjoy2012 » Sun Feb 25, 2018 5:49 pm

1) The only proper method to size the furnace/AC for your house is by doing a Manual J heat load calc. Contractors coming out to give you a bid SHOULD be measuring the window sizes of all windows, noting which side (N/S/E/W) of the house they're on, the level of energy efficiency of those windows & doors, etc. Anyone walk in and just saying "100k BTU" or "5 ton" should probably be thrown out the door immediately.

2) I would ignore any sizing recommendations listed in this thread, as people here are located in very different geographies that have very different climates.

3) A 2 stage furnace will provide more comfort than a single (in terms of noise pollution, keep the house at more steady temp, (de-)humidification, etc.). And modulating furnaces will provide even more comfort.

4) If you live in a cold climate, I'd spend more on your furnace than AC. If in a hot climate, more on the AC than furnace.

5) Lastly, I'd avoid Goodman like the plague. Install quality is just as important as the equipment, but still...

livesoft
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by livesoft » Sun Feb 25, 2018 5:57 pm

killjoy2012 wrote:
Sun Feb 25, 2018 5:49 pm
3) A 2 stage furnace will provide more comfort than a single (in terms of noise pollution, keep the house at more steady temp, (de-)humidification, etc.). And modulating furnaces will provide even more comfort.
I bet most people would not even notice that a two-stage was more comfortable if the single stage was already doing a good job of that.

Also, these responses read like a 2-stage almost never kicks in whatever the second stage is anyways, so that one is paying 2-stage prices for a one-stage life.

OTOH, maybe our 2 HVAC house is like a 2-stage only better because of the redundancy.
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asahopkins
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by asahopkins » Sun Feb 25, 2018 6:11 pm

I have found that Nate Adams has a lot of smart, if somewhat unorthodox things to say about comfort and HVAC choices. Check out the HVAC 101 chapter available for download from here:
http://www.natethehousewhisperer.com/co ... uides.html
Short take is that he would likely recommend the smallest system you can get away with, and that it should be multi-stage or modulating.

DVA79
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by DVA79 » Sun Feb 25, 2018 6:34 pm

SpaethCo wrote:
Sun Feb 25, 2018 4:44 pm
For temperature consistency, maybe consider something like https://www.ecobee.com/ for a thermostat. You can place tiny watch-battery powered temperature/motion sensors around the house so that the stat has more data to use for determining the temperature. Say you had a 4 degree spread between upstairs and downstairs, it will try and split the difference where one floor will be 2 degrees below set point, the other floor will be 2 degrees above set point. You can also have profiles like "sleeping" where it will only take the upstairs temperature probes into consideration.

For 2100sq ft house in Minnesota, we just replaced a builder's original 90,000 BTU 80% efficient furnace with a 60,000 BTU 96% efficient2 2-stage furnace. The biggest surprise is that the 2nd stage only runs when the system recovers from an auto-away/auto-home setback. (The Ecobee won't let the house get colder than what it can recover to set point at stage 2 within 30 minutes) Even on the days where it was -18F, the house had no problem maintaining a 72F set point staying in stage 1.

The thermostat makes a big difference. If you don't get a 2-stage stat, they make the furnace control when the 2nd stage kicks in based on runtime, but it's a ridiculously poor solution. (IMO)
Appreciate the response. I have read a ton on the ecobee and like how I could customize the settings, especially for a 2-stage. I will have to run a couple more thermostat wires but that be easy as I have access to that in the basement. The idea of having a room sensor upstairs to balance out the temps make me more inclined to get the two-speed since the stat would also be influenced by upstairs temp instead of just at the stat.

As for this: "The Ecobee won't let the house get colder than what it can recover to set point at stage 2 within 30 minutes" --is that a built in function of the ecobee or do you have it set to that? I read through the manual and am a little confused on the two-stage settings.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by DVA79 » Sun Feb 25, 2018 6:43 pm

killjoy2012 wrote:
Sun Feb 25, 2018 5:49 pm
1) The only proper method to size the furnace/AC for your house is by doing a Manual J heat load calc. Contractors coming out to give you a bid SHOULD be measuring the window sizes of all windows, noting which side (N/S/E/W) of the house they're on, the level of energy efficiency of those windows & doors, etc. Anyone walk in and just saying "100k BTU" or "5 ton" should probably be thrown out the door immediately.

2) I would ignore any sizing recommendations listed in this thread, as people here are located in very different geographies that have very different climates.

3) A 2 stage furnace will provide more comfort than a single (in terms of noise pollution, keep the house at more steady temp, (de-)humidification, etc.). And modulating furnaces will provide even more comfort.

4) If you live in a cold climate, I'd spend more on your furnace than AC. If in a hot climate, more on the AC than furnace.

5) Lastly, I'd avoid Goodman like the plague. Install quality is just as important as the equipment, but still...
I have had 4 contractors and none of them offered to a manual load. The houses in our neighborhood are all similar (tract houses) in size and I suspect they have been in this area many times.

One of the contractors did remove my blower fan and said I had a hairline crack in the heat exchanger (he showed me what looked like a hairline scratch on a camera). Wasnt sure if this was a play or not. There are no CO2 leaks (I have detectors all over that measure exact PPM and each shows 0) and he said it wasn't an emergency but something I need to get taken care of. Another contractor told me most heat exchangers 15+ years old may have hairline cracks and they pose no danger to the home owner since the furnace will shut off before any danger presents itself. My furnace also doesn't show any other symptoms of having a crack (like flame roll-out), but either way, it is nearing 20 years and I would rather be proactive.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by DVA79 » Sun Feb 25, 2018 7:01 pm

Any one have thoughts on getting better pricing by waiting a month or two? Heating season will be over and AC season not yet started so contractors may be looking for work.

My quotes have been the following:

-Contractor #1: Carrier: Furnace: 120,000 BTU (2- stage 96%), AC: 5 ton (single stage) - $10,800

-Contractor #2: Heil: Furnace: 100,000 BTU (2-stage 96%), AC: 4 ton (single stage) - $8,010 (add $460 for the aprilaire air filter he recommended also installing--not sure if I would do this as I haven't read much on these yet).

-Contractor #3: Goodman: Furnace 100,000 BTU (2-stage 96%), AC: 5 ton (single stage) - $6789 (this contractor works from his house and does not appear as professional as the other, but has been in the business for 25+ years).

What do you all think of these prices?

I have know that Carrier and Heil both have the same parent company and are pretty similar in quality (although Carrier has better branding) -- not sure If the higher cost of Carrier is worth it. May try to get this quote down with a smaller sized equipment.

I have read conflicting things on Goodman. They do appear a bit lower ended and you can buy them online and DIY the job. I suspect that is where much of the quality issue might come from (poor installs).

I will also get about $600 back in rebate from power/gas companies.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by mortfree » Sun Feb 25, 2018 7:22 pm

You meant CO not CO2

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by RetiredAL » Sun Feb 25, 2018 7:54 pm

DVA79,

If you don't have enough air flow to the most distant location, you will never achieve a decent comfort level, heat or cool.

In general, the larger the heater size, the higher the air capacity it will have. Air capacity is reduced by the AC's coils. In general, the larger the AC is, the larger its coils will be, thus less resistance at a given air flow.

Your current 135,000 80% heater has an output of 108,000 btu. A 100,000 96% heater will output 96,000 btu. The 120,000 96% heater will output 115,000 btu. In general, the outlet air temp between the 100,000 and 120,000 units will be similar and the heat transfer/delivery difference will from higher air flow.

A 2 stage system, if set up for maximum economy, will slow down the fan when running at stage 1. The delivered air temp, compared to the outlet air temp, will hardly vary with duct length, unless its a very long duct thru a long unheated area, so lower air low does not in general equate to lower temps due to losses.

If you go with a 2-stage and find that on low it does not deliver the heat you want, then you wire the fan to run at max both on stages, but this negates the energy savings ( electric ) you though you thought would save. If you force the heater burners to run at stage 2 (high ) full time, you will likely not be at 96%, as the Mfg was betting the much of the time you would be on low, thus they used a smaller heat exchanger.

Lastly, if generally satisfied with your current setup, the old saying "if its not broke, don't fix it" applies. Thus if it were me, I'd go with the 120,000btu / 5ton as the nearest replacement to what you currently have that seems to work.

As for 2 stage heater, as said by others, you add complexity and $$$, and that most/all of that savings could go down the drain if you have to dink with its control scheme to achieve enough air for comfort on those coldest days in the Windy City. That said, a good installer knows what generally works in your area, so don't discount him too much, but remember you have to live with it.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by SpaethCo » Sun Feb 25, 2018 11:57 pm

DVA79 wrote:
Sun Feb 25, 2018 6:34 pm
As for this: "The Ecobee won't let the house get colder than what it can recover to set point at stage 2 within 30 minutes" --is that a built in function of the ecobee or do you have it set to that? I read through the manual and am a little confused on the two-stage settings.
It's a built-in function for auto-away, although the thresholds aren't user editable. (unfortunately) For example, it only goes into auto-away after it hasn't detected movement for 2 hours. The 30 minute recovery is also not user configurable. The system is Internet connected so it gets outside temp information via nearby weather stations, and it constantly learns both how much heat your house naturally gains/loses, and how quickly the furnace/AC unit is able to drive a temperature change.

Smart recovery is another great feature that uses that information. It will automatically start running low-stage heating or cooling (if configured) to reach a set point by the scheduled time.

When it's -18F outside, at 2am it will start warming the house up from 65F to 72F starting by starting the quiet 1st stage to reach the desired temp by 7am.

When it's 30F outside, it will start around 6:15am to achieve the same results.

The benefit of the ECM blower that ramps up slowly + low stage heat is that it is almost completely silent.

Another great benefit is the stat controls my humidifier, and automatically adjusts the humidity set point in relation to the outside temp so that my windows never collect moisture.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by dccboone » Mon Feb 26, 2018 1:18 am

I would ask two questions from any company providing a bid: What is the cost to replace the motor? How much time is normally required to get the replacement part? I believe you will have your answer once the companies provide this information for both 1 and 2 stage units. Hope this helps.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by hand » Mon Feb 26, 2018 8:50 am

2500 sq ft house in the NorthEast... Short feedback is that we went with a 2 stage Bryant (Carrier) gas furnace, sized down the A/C and invested in a web connected thermostat. We've been very happy with all three decisions. The two stage furnace runs on low the vast majority of the time which is hard to notice without effort - just constant quiet well balanced heat.

Longer version is that it took some work for me to get a good system from the installers who seemed happy to bumble along replacing like for like and perpetuating the oversized and under-performing systems - nobody calls back an installer for a system that provides too much heat or too much cooling; the extra cost, reduced efficiency and reduced comfort are difficult to quantify. Ultimately, I had to run my own Manual J to get the numbers to support appropriate system sizing and tell the installer to make the A/C smaller than suggested.

A couple things to note:
1) Downsides of a too-small furnace are lag time to heat a totally cold house to temperature (mitigated by WiFi / smart thermostat) and ability to keep house exactly at design temp on the absolutely coldest day (put on a sweater once every couple of years). While these are potentially deal breaking issues for an installer, they seem like minor inconveniences to most people especially when balanced against increased efficiency and increased comfort of a system capable of constantly and evenly warming the house on typical winter days - fewer cold spots, less imbalance between floors, better air circulation.

2) For the A/C, sizing is even more important if you live in a humid climate. Efficiency aside, ideally, you want your A/C running almost 100% of the time on typical days to pull as much humidity out of the air as possible. Trade off is time to cool an un-conditioned house, and perhaps a slight rise in interior temperature on the occasional unusually hot day.

3) Smart WiFi thermostat is great at mitigating the biggest downside of properly sized systems - time to condition an unconditioned house. In the common cases of heating / cooling a house for wake-up / return from work, the smart functionality knows how long it will take to condition the house and plans accordingly. For the less common, but more frustrating return home to a freezing / sweltering house after a week away, the WiFi functionality is great - turn on your heat / A/C before you begin your trip home, and system will have the extra time it needs to condition the house before you arrive.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by livesoft » Mon Feb 26, 2018 9:45 am

@SpaethCo & @hand, thanks for taking the time to explain these smart thermostat and controls.

Our thermostats from the early 1990s have no smarts, but do allow one to have Wake, Leave, Return, Sleep time ranges (M-F, Sat, Sun) and set points along with a temporary temp override. These thermostats have separate temps heating and cooling. In essence, I think one can mimic the newer smart thermostat functions relatively easily if one sets the time/temp ranges, but there are 24 separate settings to program:

2: Heat/Cool
3: Day: M-F, Sat, Sun
4: Time: Wake, Leave, Return, Sleep
24: 2 x 3 x 4

I would not be surprised if some folks with similar thermostats just put in one temperature for all 24 settings.
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by hand » Mon Feb 26, 2018 10:21 am

livesoft wrote:
Mon Feb 26, 2018 9:45 am
@SpaethCo & @hand, thanks for taking the time to explain these smart thermostat and controls.

Our thermostats from the early 1990s have no smarts, but do allow one to have Wake, Leave, Return, Sleep time ranges (M-F, Sat, Sun) and set points along with a temporary temp override. These thermostats have separate temps heating and cooling. In essence, I think one can mimic the newer smart thermostat functions relatively easily if one sets the time/temp ranges, but there are 24 separate settings to program:

2: Heat/Cool
3: Day: M-F, Sat, Sun
4: Time: Wake, Leave, Return, Sleep
24: 2 x 3 x 4

I would not be surprised if some folks with similar thermostats just put in one temperature for all 24 settings.
While I agree with your assessment that there is a complexity hurdle that is likely too high for some (many?) users, modern smart thermostats may have additional functionality that makes them even more valuable than the 1990s versions:

1) Ability to monitor outside temperature and home heating / cooling performance to deliver a specific temperature at a specific time (e.g. 68 degrees at 5pm) rather than simply turning on the heat at 5pm.

2) Ability to manage cooling to hit a humidity target rather than simply hit a temperature target that might still leave the house uncomfortable

3) Web connectivity allows for a) a better user interface and management of all of the complexity) b) remote operation of the HVAC system.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by lthenderson » Mon Feb 26, 2018 10:39 am

DVA79 wrote:
Sun Feb 25, 2018 3:15 pm
Furnace Questions:
Did you go with 1-stage or 2-stage? Do you like the 2-stage? Does it heat upstairs during low stage? Have you noticed energy savings? How is the sound? If you have similar sq footage, what BTU size furnace did you go with? Some tell me 2-stage furnaces are more prone to breakdown and other say this is untrue—what has your experience been?
We replaced a 25 year old 1-stage with a 2-stage about five years ago. If I had to do it again, I would do it the same. I really love having a furnace that runs without noise. The only time the second stage ever kicks on is in the cold mornings when it brings the house up to temp. Other than that it runs on the first stage only which you can't hear working.

We did see a significant energy savings but I think it was mostly due to increased efficiencies and 25 years of better technology.

There are no difference in number of moving parts between a single stage and a dual stage so I would expect they would have similar lifetimes.

My first rule of thumb when buying any appliance or mechanical unit for my house has always been to ask the local repair person which brands they recommend. They repair these things daily so can definitely steer you away from those brands prone to breaking down.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by TareNeko » Mon Feb 26, 2018 10:56 am

The idea of 2-stage and multi-stage furnaces is that they run longer at lower heat output. This way the fan doesn't have to run at high speed, which reduces noise. Also as the furnace runs for longer periods, it helps to maintain more even temperatures.

I don't think it makes sense to say why pay 2nd stage prices if it never kicks-in. I did manual J calculation for my house, and depending on outdoor temperature, my heat load varies from 24000btu to 47000btu. To me, it makes more sense to have a furnace that can adjust its heat output based on demand. For that reason I actually bought variable speed furnace which can adjust its heat output from 40% to 100%. You never hear the thing running, it is that quite.

Aside from the number of stages, I definitely suggest a furnace with variable speed motor. You can set this to a low setting and it will circulate the air constantly and when the furnace turns on, the fan speed increases to deliver heat. This helps evening out the temperature of downstairs and upstairs. Of course, a furnace per level is the best way, but not always possible.

livesoft wrote:
Sun Feb 25, 2018 5:57 pm
killjoy2012 wrote:
Sun Feb 25, 2018 5:49 pm
3) A 2 stage furnace will provide more comfort than a single (in terms of noise pollution, keep the house at more steady temp, (de-)humidification, etc.). And modulating furnaces will provide even more comfort.
I bet most people would not even notice that a two-stage was more comfortable if the single stage was already doing a good job of that.

Also, these responses read like a 2-stage almost never kicks in whatever the second stage is anyways, so that one is paying 2-stage prices for a one-stage life.

OTOH, maybe our 2 HVAC house is like a 2-stage only better because of the redundancy.
Last edited by TareNeko on Mon Feb 26, 2018 11:10 am, edited 2 times in total.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by TareNeko » Mon Feb 26, 2018 11:04 am

The OP has 135k btu, 80% efficient unit, which puts out 108k btu, when it was new. So probably it is lower than that now. Even buying a 120k btu 96% efficient unit will be too much. I would look into 100k btu, 95+% efficient units.

The thing is, the max BTU rating is only useful when you need to heat up the house. So if the unit is slightly undersized, it will just take extra 15mins to heat up the house in a really cold morning. But if you buy a furnace that is too big, than it will cycle on/off too often, which is less efficient, more noisy, and causes shorter life for the furnace. You never need the max BTU rating of a furnace after the house is warmed up. You need 20-40% of the max rating, maybe. So buying the next size up doesn't make any sense.

RetiredAL wrote:
Sun Feb 25, 2018 7:54 pm
Lastly, if generally satisfied with your current setup, the old saying "if its not broke, don't fix it" applies. Thus if it were me, I'd go with the 120,000btu / 5ton as the nearest replacement to what you currently have that seems to work.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by Valuethinker » Mon Feb 26, 2018 11:14 am

DVA79 wrote:
Sun Feb 25, 2018 4:02 pm
bubbadog wrote:
Sun Feb 25, 2018 3:42 pm
I have a 3,000 SF home in the Midwest. I replaced my central air unit 4 years ago with a heat pump version. It is my understanding that the heat pump is cheaper to operate than the natural gas furnace until it gets too cold outside (30-35 degrees?). My existing single stage natural gas furnace then kicks in for colder temps. The heat pump version was about $500 more than a comparable central air unit. Have you explored this option?
Interesting. I don’t know anything about heat pumps—is this part of the AC unit?
A HP is really just an AC that can be reversed. Or more a fridge, really.

So when you need AC, it cools the inside of your house, like a fridge. But when you need heat, it runs in reverse, and cools the outside air and heats the air in your house.

Efficiency of (Air Source) Heat Pumps falls as the gap between internal and external air temperatures grows. Thus they are often used in US Southeast, where the winter temperatures are not usually too cold, but AC is a necessity for many months of the year. Saves the developer the cost of installing gas pipelines (if they are even available).

One key metric is Coefficient of Performance. For 1 kwhr of electricity running the ASHP, how many kwhr of heat/ cold are moved. Anything about 3.0 in normal operation is good. 1.0 is equivalent to electric resistance (bar) heating -- they usually have a backup that kicks in. It seems that good modern ASHPs run above 1.0 down to say 20 F (others may chip in - I am not based in USA and the technology is relatively rare in UK where 80% homes are on gas). A gas furnace (high efficiency) runs a COP of about 0.9 for comparison. Say your Electricity is 10 c/ kwhr then breakeven with gas for heating is typically 4 c/ kwhr for gas (1 kwhr = 3412 BTU of gas).

We have at least one poster here (just frank) who is very happy with his HP installation in Mid Atlantic/ Pennsylvania climate (natural gas was not available to him).

With a home more than 50 years old, the insulation may just not be good enough. The ASHP won't warm a house up as fast as a gas furnace (which usually has a much higher BTU) -- ASHP work best if run nearly continuously but at a lower temperature (they thus work particularly well w underfloor "hydronic" heating systems).

(Geothermal or Ground Source Heat Pumps are potentially much more efficient (COP up to 5.0) because the ground has almost constant temperature all year round, but the cost of installation and the hassle is significant - -long trench or vertical bore).

An ASHP should not cost a lot more than a comparable AC, because the basic technology and hardware are the same. Most of the time people seem to install a "split" with one box inside the house, and one outside.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by KT785 » Mon Feb 26, 2018 11:24 am

DVA79 wrote:
Sun Feb 25, 2018 6:43 pm
killjoy2012 wrote:
Sun Feb 25, 2018 5:49 pm
1) The only proper method to size the furnace/AC for your house is by doing a Manual J heat load calc. Contractors coming out to give you a bid SHOULD be measuring the window sizes of all windows, noting which side (N/S/E/W) of the house they're on, the level of energy efficiency of those windows & doors, etc. Anyone walk in and just saying "100k BTU" or "5 ton" should probably be thrown out the door immediately.

2) I would ignore any sizing recommendations listed in this thread, as people here are located in very different geographies that have very different climates.

3) A 2 stage furnace will provide more comfort than a single (in terms of noise pollution, keep the house at more steady temp, (de-)humidification, etc.). And modulating furnaces will provide even more comfort.

4) If you live in a cold climate, I'd spend more on your furnace than AC. If in a hot climate, more on the AC than furnace.

5) Lastly, I'd avoid Goodman like the plague. Install quality is just as important as the equipment, but still...
I have had 4 contractors and none of them offered to a manual load. The houses in our neighborhood are all similar (tract houses) in size and I suspect they have been in this area many times.
Then I'd probably find a new contractor.

New HVAC equipment is a pricey update and accordingly, you should be comfortable that it's sized correctly to your home and the variables inherent therein. I live in northern/central Illinois and replaced our HVAC system in 2016 and a few of the contractors who gave quotes eyeballed it based on their work in the neighborhood or based on the original equipment (20 years old); two other contractors were very thorough from the outset and provided me with the load calculations along with the estimate. I went with one of those contractors as conducting the calculation as part of the work-up gave me an indication of how they'd handle the job in its entirety.

For the data point you requested: we have a 3,500 sq. ft. house and put in a 100,000 BTU Trane two-stage, variable speed 96% efficient furnace. The house is certainly more evenly heated now and our gas bill is lower (though the original furnace was a 90+% Carrier unit). We replaced the AC as well and our cooling costs dropped quite a bit, and the house is much drier in the summer . . . of what I recall of my research at the time, the variable speed fan actually drives a lot of the benefit of the newer systems, both for heating and cooling. I believe my systems also has some "smart" sensors that adjust the fan on the fly based on duct pressure which may help with getting better airflow to the second story.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by Big Dog » Mon Feb 26, 2018 11:42 am

For comfort, generally the longer the a/c or furnace runs, the better.
Exactly. And that is why purposely buying an oversized unit is not recommended (and very Un-BH like).

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by livesoft » Mon Feb 26, 2018 12:14 pm

hand wrote:
Mon Feb 26, 2018 10:21 am
1) Ability to monitor outside temperature and home heating / cooling performance to deliver a specific temperature at a specific time (e.g. 68 degrees at 5pm) rather than simply turning on the heat at 5pm.
Heat would not be turned on at 5 pm unless the Return temp was 68 deg, the Leave temp was less 68 deg, AND the internal house temp was colder than 68 deg. The outside temp would be automatically included because if it wasn't cold outside, then the inside house temp would not be below 68 deg.

I never considered home layout before in all this, but now I see that:

Our HVAC systems are in the attic above the 2nd floor in practically the middle of the house. That is, they are not at either end.
As a consequence, the ductwork is like a spider pattern with short runs to every room. The return ducts are directly below the HVAC units and the intakes are 16 x 32 inch just below the wall-mounted thermostats. The filters are custom washable filters since they are so large.

There is a also open staircase connecting the two floors in the center of the home by the thermostats, so some air mixing occurs there.

As for noise, it seems that our Bosch dishwasher is noisier than our fridge, is noisier than our HVAC.

I expect that the grillwork on the vents in each room may be more of noise factor because they can restrict the airflow near one's ears. We don't hear the furnaces units themselves since they are in the attic. The outdoor compressors for the AC units are outside on a brick wall nowhere near any windows, so I expect the neighbors to hear more noise from them than we do.

Now all the above are not something that one can change after they own a house, but if one is looking at homes, then the layout and location of the HVAC system might be something to consider.
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by hand » Mon Feb 26, 2018 3:39 pm

livesoft wrote:
Mon Feb 26, 2018 12:14 pm
hand wrote:
Mon Feb 26, 2018 10:21 am
1) Ability to monitor outside temperature and home heating / cooling performance to deliver a specific temperature at a specific time (e.g. 68 degrees at 5pm) rather than simply turning on the heat at 5pm.
Heat would not be turned on at 5 pm unless the Return temp was 68 deg, the Leave temp was less 68 deg, AND the internal house temp was colder than 68 deg. The outside temp would be automatically included because if it wasn't cold outside, then the inside house temp would not be below 68 deg.
I think we may be talking past each other, or I'm simply being unclear.

Failure mode for a properly sized or undersized furnace or A/C is that it takes too long for an unconditioned house to come to temperature.

With a "dumb" programmable thermostat, Sequence is approximately as follows:

At 5pm heat is turned on because thermostat is changed from away mode (60 degrees) to home mode (70 degrees) and house under temp. Because it is a cold day (0 degrees) heater takes two hours to bring temperature to 70 degrees at 7pm. Homeowner complains that furnace is undersized (and it is for this specific use case).

Smart functionality is roughly as follows:

Thermostat knows that house is supposed to be 70 degrees at 5pm, recognizes outside temperature is unusually cold (0 degrees) and estimates that heat should be turned up at 3pm to meet 5pm target temperature. Homeowner is happy with furnace sizing because lower peak heating ability is offset by "smart" thermostat's ability to turn up heat early when needed.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by bloom2708 » Mon Feb 26, 2018 3:59 pm

Lots of technical stuff happening.

I would go with the 2 stage for both heat/cool.

Our Lennox is actually variable staged but to do that you need their thermostat. We use an ecobee3 with our 2 stage system.

The lower stage is virtually silent. You cannot hear it run. It only kicks up into the 2nd stage if needed. Very cold or very warm out.

A smart thermostat, keeping the fan only going for 40-50 mins/hour and the dual stage allow our house to stay quite comfortable.
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by livesoft » Mon Feb 26, 2018 5:19 pm

hand wrote:
Mon Feb 26, 2018 3:39 pm
[...]
I think we may be talking past each other, or I'm simply being unclear.
I get it, but I don't believe it for our home's situation.

I might suggest that rather than spending an extra $2,000 to $4,000 or more for a fancy schmancy HVAC plant, that one spend the money for better insulation of the home.
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by Epsilon Delta » Mon Feb 26, 2018 6:36 pm

hand wrote:
Mon Feb 26, 2018 3:39 pm
Smart functionality is roughly as follows:

Thermostat knows that house is supposed to be 70 degrees at 5pm, recognizes outside temperature is unusually cold (0 degrees) and estimates that heat should be turned up at 3pm to meet 5pm target temperature. Homeowner is happy with furnace sizing because lower peak heating ability is offset by "smart" thermostat's ability to turn up heat early when needed.
Notice there is another way to do this without an outside temperature sensor:
While the house is in away mode notice how fast the temperature is dropping, and if the heat is cycled on how fast the temperature rises. This allows the thermostat to calculate how long it will take the house to heat up.

Notice that more insulation only helps to the extent that the extra insulation results in an over-sized furnace. Up the insulation, re-do manual J to find the correct furnace size and your back to where you started.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by jebmke » Mon Feb 26, 2018 6:54 pm

Valuethinker wrote:
Mon Feb 26, 2018 11:14 am
We have at least one poster here (just frank) who is very happy with his HP installation in Mid Atlantic/ Pennsylvania climate (natural gas was not available to him).
We are on HP in Maryland. No gas available. We have 2-stage 16 SEER system. Electric heat strips cut in when very cold and need to get temps up. But I have seen the unit running in HP mode (no strips) with outside temps in the low teens (F). We have put in a lot of additional insulation and replaced many of the windows. The two stage system is very comfortable. Runs at low speed most of the time.
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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by il0kin » Mon Feb 26, 2018 8:31 pm

We replaced a 3.5 ton with a 4 ton Lennox last spring. 2500 sq. ft of two-level living, 750 sq ft of finished basement. We are in Kansas, it gets much warmer than Chicago. 2nd floor has been much more comfortable since we went to the 4 ton. Single stage - happy with it. Calculated energy savings and went with 13 SEER, even the 14 wasn't worth it for cost savings in the long run. Make sure the company you contract pulls inspection permits, that's the key to a good install, it keeps them honest and MANY companies, even major ones, don't bother with permitting.

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Re: AC/Furnace Questions- 1 stage or 2 stage?

Post by ncbill » Tue Feb 27, 2018 12:11 pm

livesoft wrote:
Mon Feb 26, 2018 5:19 pm
hand wrote:
Mon Feb 26, 2018 3:39 pm
[...]
I think we may be talking past each other, or I'm simply being unclear.
I get it, but I don't believe it for our home's situation.

I might suggest that rather than spending an extra $2,000 to $4,000 or more for a fancy schmancy HVAC plant, that one spend the money for better insulation of the home.
And having a contractor do a blower test and air sealing (don't want conditioned air escaping into unconditioned spaces)

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