HVAC replacement when experts disagree

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jco
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Re: HVAC replacement when experts disagree

Post by jco »

UALflyer wrote: Wed Apr 28, 2021 1:54 pm
jco wrote: Mon Apr 26, 2021 11:31 amBased on UALflyer's questions below:

Have any contractors checked the refrigerant pressure to ensure that it's not low?
- No, since we want to replace the system. The fan motor is definitely bad. And R22 is so expensive. So they're focusing on replacement. Even an independent HVAC servicer that doesn't do installs suggested I get it replaced.
I understand that, but am trying to figure out the reason that you've been dissatisfied with the a/c performance. If, for instance, the R22 pressure has been low for a while, it would explain the reason that it hasn't been cooling well.
Have any contractors looked at the supply and return vents and confirmed that the pressure is balanced?
- I don't think so. A couple have commented on removing the return vents up the ceiling in our upstairs bedrooms to improve cooling in the summer. They have said that the supply vents are not designed well and that there is probably a lot of turbuluence. These professionals suggested installed scoops and dividers to better direct the airflow.
Do get them to focus on the ductwork and see if you can get more useful info out of them. If there's an issue with the ductwork, adding a/c tonnage may not help and could actually hurt.

You can't come up with a good solution without knowing the exact source of your problem.
What tonnage are the ducts sized for?
- No idea, but our furnace is 110,000 BTU with a 5-ton blower (learned this today). So probably pretty big.
I wouldn't assume anything and get contractors to look at the ducts and figure it out, which should only take 5 minutes. You can't even talk about the tonnage without knowing what the ductwork is designed to handle.
Is your furnace in the attic or in the basement?
- Basement
This is good and bad. It's good because basements are naturally much cooler, so the a/c doesn't have to struggle with attic temperatures. It's bad because you've got a single a/c cooling both floors, and the fact that the furnace is in the basement means that the upstairs supply is located pretty far from the unit. This probably means that the upstairs rooms are getting less airflow and higher temperatures than the downstairs rooms, all while the upstairs rooms are already naturally warmer (heat rises).
What type of air filter do you use (how thick and what MERV rating) and how often do you replace it?
- 1" with a MERV of 4, which is about as flimsy as I could find. I usually change them every 2 or 3 months. My nest reminds me to change them.
Good, so it's not that.
Thanks UALFlyer. I'll try to get a bit more info from the installers in the coming days!
alfaspider
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Re: HVAC replacement when experts disagree

Post by alfaspider »

talzara wrote: Wed Apr 28, 2021 1:59 pm
alfaspider wrote: Wed Apr 28, 2021 1:18 pm That's the problem though. Sometimes you get 99.99th percentile temperature. Plus, they are often based off inaccurate assumptions of what 99th percentile is. All I know is I've seen many an "oversized" a/c unit fail to keep up on extremely hot days.
The 99th percentile in Manual J is based on Weather Service data over 30 years. HVAC contractors often increase the temperature to sell larger equipment. Nobody ever decreases it.

If an oversized air conditioner can't keep up on extremely hot days, then something is wrong with the air conditioner, the duct system, or the building envelope.

The residential HVAC industry likes to sell new equipment. They don't like to solve problems. It takes too long and requires too much math, and they get paid less.
Well, climate has been changing over 30 years. There are more extreme temperature days than there was. You also have to account for having a party in August where you have 30 people and outside doors are being opened regularly. I believe those calculations are always going to assume a normal number of people and doors remaining closed.
Last edited by alfaspider on Wed Apr 28, 2021 3:41 pm, edited 1 time in total.
UALflyer
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Re: HVAC replacement when experts disagree

Post by UALflyer »

plumberboy wrote: Wed Apr 28, 2021 2:31 pm From the information you gave I would go with the 3.5 or 4.0 ton 2 stage unit and a 2 stage furnace with a variable speed blower.You will not be sorry for going with the 2 stage unit and variable speed blower. I speak from personal experience.
All blower motors are now "variable speed," which just means an ECM blower motor: https://www.anthonyphc.com/blog/ecm-fan-motor-mandate/
When the a/c operates in the 1st stage it only uses 1/2 the power it uses in the second stage.
That's incorrect. Different manufacturers implement this differently, but it's very common for the 1st stage to run at 70% to 80% of the 2nd stage.

The OP has two floors and the furnace (which also means the blower fan) is in the basement, which reduces the amount of airflow that the second floor receives. A 2 stage system will only exacerbate this issue for him.
plumberboy
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Re: HVAC replacement when experts disagree

Post by plumberboy »

UALflyer wrote: Wed Apr 28, 2021 2:53 pm
plumberboy wrote: Wed Apr 28, 2021 2:31 pm From the information you gave I would go with the 3.5 or 4.0 ton 2 stage unit and a 2 stage furnace with a variable speed blower.You will not be sorry for going with the 2 stage unit and variable speed blower. I speak from personal experience.
All blower motors are now "variable speed," which just means an ECM blower motor: https://www.anthonyphc.com/blog/ecm-fan-motor-mandate/

Not so. There are ECM motors that are one speed, there are ECM motors that vary their speed according to need that are controlled by a board and there are motors that are multi speed that run at a preset speed for heating or cooling.

When the a/c operates in the 1st stage it only uses 1/2 the power it uses in the second stage.
That's incorrect. Different manufacturers implement this differently, but it's very common for the 1st stage to run at 70% to 80% of the 2nd stage.

The OP has two floors and the furnace (which also means the blower fan) is in the basement, which reduces the amount of airflow that the second floor receives. A 2 stage system will only exacerbate this issue for him.
You may be right that the 1st stage uses more than 50% power but the point is it uses much less power.
As for a 2 story, it depends on the location of the thermostat and the setting for when the 2nd stage activates. The best way to heat or cool a 2 story is separate zones for each or individual heating and cooling systems for each level.
Joylush
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Re: HVAC replacement when experts disagree

Post by Joylush »

Make sure you a large enough return. This is especially important when you have a variable speed air handler. Many installations are done without enough return and that can greatly affect performance.
GuyInFL
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Re: HVAC replacement when experts disagree

Post by GuyInFL »

UALflyer wrote: Wed Apr 28, 2021 1:54 pm
jco wrote: Mon Apr 26, 2021 11:31 am
What tonnage are the ducts sized for?
- No idea, but our furnace is 110,000 BTU with a 5-ton blower (learned this today). So probably pretty big.
I wouldn't assume anything and get contractors to look at the ducts and figure it out, which should only take 5 minutes. You can't even talk about the tonnage without knowing what the ductwork is designed to handle.
So how do you determine duct size tonnage?
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StevieG72
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Re: HVAC replacement when experts disagree

Post by StevieG72 »

That is a big difference! FWIW I have an install crew in my home right now, went from a 2 ton unit to 2.5. My understanding is you can wiggle around plus or minus 1/2 ton. Of course in my situation up would be the only option don't think they have 1.5 ton who knows. The company that quoted the job was very knowledgeable, and took time to explain the details. The explanation to me to bump up to a 2.5 ton would be appreciated on the hottest days of the summer with 1000% humidity that we experience on the southern coast of Va. We get two seasons, cold and scorching hot, not a whole lot of in between. Fun fact my air handled for the heat-pump is 35 years old!?! Outdoor compressor over 20 yrs old! I am replacing the entire system including ductwork.

For your situation dropping to a 2.5 ton from a 3.5 seems a bit extreme. However if you don't have much humidity maybe it may work just fine.
Fools think their own way is right, but the wise listen to others.
talzara
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Re: HVAC replacement when experts disagree

Post by talzara »

tibbitts wrote: Wed Apr 28, 2021 2:32 pm Sometimes solving all the other "little" problems that add up to making the "correct" amount of cooling just barely adequate costs a lot more than the next size hvac and the extra cost to run it for whatever the life of it is.
I replied to a post that said an "oversized" system could not keep up. It did not say that a "barely adequate" system could not keep up.

You can keep making it bigger and bigger, but the system is already oversized. It's better to solve the actual problem, even if it costs more than putting in a new system.

There are a lot of HVAC threads on Bogleheads that complain about one room, one floor, or an addition being hotter than the rest of the house. Oversizing the central air conditioner will not solve the problem. You need to add zoning dampers, more insulation, more supplies, more returns, or a mini-split.
talzara
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Re: HVAC replacement when experts disagree

Post by talzara »

alfaspider wrote: Wed Apr 28, 2021 2:46 pm Well, climate has been changing over 30 years. There are more extreme temperature days than there was. You also have to account for having a party in August where you have 30 people and outside doors are being opened regularly. I believe those calculations are always going to assume a normal number of people and doors remaining closed.
The National Weather Service will be releasing new 30-year climate normals next month. The 99th percentile temperature will probably go up by about 1 degree from 10 years ago. The average residential air conditioner in the United States is oversized by 50-100%. One degree won't make them correctly-sized.

Opening the door has very little effect on air conditioner runtime, as long as you don't leave it open. The surface area of the door is very small relative to the volume of the house. It's not a refrigerator door.

Adding people is a common trick that HVAC installers use to make the Manual J come out higher. Manual J already includes a 15% built-in oversizing factor, and Manual S rounds up to the next half-ton. Adding more people would be double-counting them.

Also, you would have to be holding parties during the hottest hours of the hottest days of the year. If you hold the party on other days, it's below the 99th percentile temperature. If you hold the party at night, it's below the 99th percentile temperature.
talzara
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Re: HVAC replacement when experts disagree

Post by talzara »

StevieG72 wrote: Thu Apr 29, 2021 8:42 am The explanation to me to bump up to a 2.5 ton would be appreciated on the hottest days of the summer with 1000% humidity that we experience on the southern coast of Va. ... For your situation dropping to a 2.5 ton from a 3.5 seems a bit extreme. However if you don't have much humidity maybe it may work just fine.
You have it backwards.

If you have a lot of humidity, then a smaller air conditioner is better. Longer runtimes remove more humidity than shorter runtimes.

If you have very little humidity, then you can make the air conditioner oversized. The air conditioner will be worse at dehumidifying, but it's not removing much humidity anyway. The only effect will be reduced efficiency.

If your house is too humid, the best solution is to improve the airtightness of the house without improving the thermal insulation. The sensible load will decrease a little, the latent load will decrease a lot, and the sensible heat ratio will go up. When the SHR of the house becomes higher than the SHR of your air conditioning coil, your house won't be humid anymore.
alfaspider
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Re: HVAC replacement when experts disagree

Post by alfaspider »

talzara wrote: Thu Apr 29, 2021 12:42 pm
alfaspider wrote: Wed Apr 28, 2021 2:46 pm Well, climate has been changing over 30 years. There are more extreme temperature days than there was. You also have to account for having a party in August where you have 30 people and outside doors are being opened regularly. I believe those calculations are always going to assume a normal number of people and doors remaining closed.
The National Weather Service will be releasing new 30-year climate normals next month. The 99th percentile temperature will probably go up by about 1 degree from 10 years ago. The average residential air conditioner in the United States is oversized by 50-100%. One degree won't make them correctly-sized.

Opening the door has very little effect on air conditioner runtime, as long as you don't leave it open. The surface area of the door is very small relative to the volume of the house. It's not a refrigerator door.

Adding people is a common trick that HVAC installers use to make the Manual J come out higher. Manual J already includes a 15% built-in oversizing factor, and Manual S rounds up to the next half-ton. Adding more people would be double-counting them.

Also, you would have to be holding parties during the hottest hours of the hottest days of the year. If you hold the party on other days, it's below the 99th percentile temperature. If you hold the party at night, it's below the 99th percentile temperature.
We usually have our parties in the afternoon. And given that summer time tends to be common for get togethers, it's not uncommon for them to end up on one of the hottest days of the year. Personal experience is during a party, the door is often always open. It makes a big difference when there's a 30* inside/outside delta.

All I'm saying is that there is a difference between theory in practice, and I don't think the installers are just upsizing to make a buck. Nobody is going to call their HVAC installer to complain because the system is short cycling or the humidity is a bit high. They will complain if they are having a summertime party and all their guests are complaining.
talzara
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Re: HVAC replacement when experts disagree

Post by talzara »

alfaspider wrote: Thu Apr 29, 2021 1:04 pm We usually have our parties in the afternoon. And given that summer time tends to be common for get togethers, it's not uncommon for them to end up on one of the hottest days of the year. Personal experience is during a party, the door is often always open. It makes a big difference when there's a 30* inside/outside delta.

All I'm saying is that there is a difference between theory in practice, and I don't think the installers are just upsizing to make a buck. Nobody is going to call their HVAC installer to complain because the system is short cycling or the humidity is a bit high. They will complain if they are having a summertime party and all their guests are complaining.
If the door is being left open during the hottest hours of the hottest days of the year, that's like having a 20 sqft hole in the side of your house. You actually need an oversized air conditioner.

There are many reasons that HVAC contractors install larger air conditioners. Homeowners usually demand larger air conditioners. They also have thermostats that display the temperature, but very few thermostats display the humidity. However, it doesn't hurt HVAC contractors make more money on larger air conditioners. If they made less money, they'd push back more strongly against oversizing.
Topic Author
jco
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Re: HVAC replacement when experts disagree

Post by jco »

UALflyer wrote: Mon Apr 26, 2021 7:10 pm Have any competent contractors actually taken a look at the ducts? If you put in a larger unit and the ducts are undersized for it, static pressure will increase, which will cause excessive noise as air moves through them (it'll also cause additional wear and tear of the unit, which will cause breakdowns; it can also cause your indoor coil to freeze up regularly). On the other hand, if you stick a smaller unit in, which causes the ducts to be oversized, you'll be reducing air flow, which will cause some rooms to receive insufficient airflow and to feel uncomfortable. Likewise, if there's an issue with your returns (too small, not enough of them, wrong location, etc...), not enough air will be pulled from certain rooms into the unit, which can also create noise (and cause additional wear and tear) and cause rooms to feel stuffy.

So, when people say "my AC does not cool enough," in many cases it'll be less about insufficient cooling capacity and more about insufficient airflow or insufficient moisture removal. In those situations, upsizing the unit can actually make the situation worse. So, you simply can't just blindly stick a larger unit in... well, you can, and incompetent contractors do this all the time, which in a lot of cases ends up only making the problem worse.
I asked someone yesterday (who seemed very competent and was building a detailed manual J.

The main supply duct is sized for a 2.5 ton A/C (the main supply is 24x8, which technically supports a 2.75 A/C). This supports 1100 CFM, and you need 400 CFM per ton of A/C. However, there are two 17x8 supply branches, that in theory, pull 750 CFM. So the main supply line seems undersized.

The return is 24x10, which is effectively a 4-ton return.

I'm now asking the contractors about upgrading the main supply. There is room.
UALflyer
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Re: HVAC replacement when experts disagree

Post by UALflyer »

jco wrote: Fri Apr 30, 2021 10:17 am
UALflyer wrote: Mon Apr 26, 2021 7:10 pm Have any competent contractors actually taken a look at the ducts? If you put in a larger unit and the ducts are undersized for it, static pressure will increase, which will cause excessive noise as air moves through them (it'll also cause additional wear and tear of the unit, which will cause breakdowns; it can also cause your indoor coil to freeze up regularly). On the other hand, if you stick a smaller unit in, which causes the ducts to be oversized, you'll be reducing air flow, which will cause some rooms to receive insufficient airflow and to feel uncomfortable. Likewise, if there's an issue with your returns (too small, not enough of them, wrong location, etc...), not enough air will be pulled from certain rooms into the unit, which can also create noise (and cause additional wear and tear) and cause rooms to feel stuffy.

So, when people say "my AC does not cool enough," in many cases it'll be less about insufficient cooling capacity and more about insufficient airflow or insufficient moisture removal. In those situations, upsizing the unit can actually make the situation worse. So, you simply can't just blindly stick a larger unit in... well, you can, and incompetent contractors do this all the time, which in a lot of cases ends up only making the problem worse.
I asked someone yesterday (who seemed very competent and was building a detailed manual J.

The main supply duct is sized for a 2.5 ton A/C (the main supply is 24x8, which technically supports a 2.75 A/C). This supports 1100 CFM, and you need 400 CFM per ton of A/C. However, there are two 17x8 supply branches, that in theory, pull 750 CFM. So the main supply line seems undersized.

The return is 24x10, which is effectively a 4-ton return.

I'm now asking the contractors about upgrading the main supply. There is room.
Excellent. Now, you're getting somewhere.

As I mentioned above, there's no way to come up with an effective solution without first figuring out the cause of the problem. Hence, the reason that it's entirely premature to talk about the needed tonnage, as blindly increasing the tonnage may not solve the problem and can even make things worse.
UALflyer
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Re: HVAC replacement when experts disagree

Post by UALflyer »

alfaspider wrote: Thu Apr 29, 2021 1:04 pm Nobody is going to call their HVAC installer to complain because the system is short cycling or the humidity is a bit high. They will complain if they are having a summertime party and all their guests are complaining.
Right, people just complain about being hot and uncomfortable. What they don't realize is that your comfort level isn't just about the temperature. Hence, for instance, if your lower the humidity, you'll frequently find higher temperatures more comfortable. On the other hand, lower temperatures, but higher humidity can be very uncomfortable. Likewise, with air movement, higher temperatures also become more comfortable.

In practical terms, if you leave the door wide open during a July party, your central a/c, regardless of its size, won't do anything anyway, as it'll have too much outdoor air to contend with. In those types of situations, large fans will be a lot more effective.

Blindly upsizing your a/c without considering your ducts or a properly calculated Manual J is like blindly sticking a giant engine into an econobox and then wondering why the econobox's handling has suddenly gotten worse.
Topic Author
jco
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Re: HVAC replacement when experts disagree

Post by jco »

Thanks to everyone who commented. After a lot of research and asking a lot of questions, I think I have a better understanding of which contractors are right (or at least close to right) and wrong when it comes to sizing and some other things.

The contractors who did the most thorough manual J recommended a 2.5 ton, 60000 BTU furnace. Some people sized up by 0.5 a ton and 20,000 BTUs on the A/C furnace. Of the 10(!) quotes I've received, I've narrowed it down to 3 contractors who have competitive rates and made me feel most comfortable about the install. All have excellent ratings from online reviews, which is about as good as you can do these days. All are planning to do some ductwork upgrades for the air supply to improve the airflow.

Now, I just need to decide on a system!
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jco
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HVAC simplicity vs efficiency choice

Post by jco »

[Thread merged into here --admin LadyGeek]

I need to get a new A/C and furnace. I've narrowed it down to three contractors. All have excellent reviews online. All have been patient and helpful in answering my questions. All of them are performing ductwork to improve the airflow coming out of my system. I think all of them are good choices. All three quotes are at similar price points but have different pros and cons. I'd love to get the wisdom of the Bogleheads to make the best choice.

My main question is whether the reliability of the higher efficiency (AFUE) furnaces is noticeably worse than the standard 80% AFUE furnaces and/or whether the maintenance costs are substantially higher? As can be seen in the table, in theory, I can get the highest efficiency system for the lowest cost after rebates! It's tempting, but if I end up having a system that breaks down all the time and lots of labor charges, then it won't be worth it. I've heard the higher AFUE furnaces are more sensitive and there are more electrical problems. Higher efficiency comes at higher complexity, so there are more points of failure.

Note: all the choices below have a 10-year parts warranty. My correct A/C sizing seems to be between 2.5 and 3 tons. Our current furnace puts out 110k BTUs at 80% AFUE. Arm. = Armstrong in option C below.

Code: Select all

System 	Cooling					Heating				Labor	Upfront Cost after rebates
A	Trane 1-speed 3 ton 13 SEER A/C		Trane 80% AFUE 2-stage 80k BTU	2 yrs	$9,200	$9,200
B	Amana 1-speed 2.5 ton 16 SEER H/P	Amana 80% AFUE 2-stage 60k BTU	10 yrs	$10,500	$9,750
C	Bosch 2-stage 4-5 ton 20 SEER H/P	Arm. 96% AFUE 2-stage 90k BTU	2 yrs	$12,500	$8,500
Option A is very traditional and has the lowest upfront cost.
Option B is a bit more, but has a higher-efficiency A/C and has an incredible labor warranty. This feels pretty safe, though the systems are smaller, which is somewhat concerning to me. The heat pump will be really, really quiet.
Option C has the largest upfront cost, but the lowest cost after rebates because of incredible rebates (that I will double-check). The A/C is larger, but because it's a two-stage system, it would only pump out more cooling if needed. The furnace is a bit larger than I expected, but it's similar sizing (account for efficiency) as our current furnace, which we've had no complaints about. The heat pump will be really, really quiet.

We're in Colorado, and based on some websites, I don't think we'd save more than $200-400 per year with the higher efficiency systems.

Are there any additional factors I should consider here? I'm tempted to go with option C and see if I can get an extended labor warranty. It's the cheapest after rebates and the most efficient. As long as it's reliable, it seems like the clear choice. The extended warranty would be paid for by the extra efficiency over time.
Last edited by jco on Sat May 01, 2021 12:27 pm, edited 1 time in total.
tibbitts
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Re: HVAC simplicity vs efficiency choice

Post by tibbitts »

My experience after a dozen years has been that the considerable trouble I've had with my variable-speed (well, two really) high-efficiency pair has been that everything that has broken has been the same parts that are in simpler systems: three coil failures due to dissimilar metals used in the design, and some dirt on the flame sensor, and a simple outside fan motor.
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Re: HVAC simplicity vs efficiency choice

Post by illumination »

Every tech I've come across has said get the simplest one, even though the more expensive one can mean they get a bigger sale. I personally put a bigger premium on reliability than utility savings. One extra service visit is not only incredibly inconvenient (I've had to live elsewhere for a week one time) it wipes out any savings. I also think you being in Colorado, AC cost savings between the best and worst are probably like $25 a month in the summer months you use it. You can play around with a SEER calculator, it's not nearly the game changer people think it is.

https://www.seerenergysavings.com/

That 10-year labor warranty though is attractive, just make sure there's not fine print like you have to have it "inspected" every year for a fee. That can change the math.

FWIW, I had a Trane 5 ton (14 SEER?) installed about a year ago with a new furnace, it was around $6,500 out the door. But COVID is being use as an excuse for everything spiking in price. American Standard is essentially the same product and can be had for a lot less.
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Re: HVAC simplicity vs efficiency choice

Post by jebmke »

We went to 2-stage heat pump (variable speed fan). One advantage of the two stage system for us is that we don't get as much drafty cooling and heating since the system can run on the lower compressor stage much of the time - and the fan runs very low for longer keeping temps much more even. So, in addition to some energy savings, we get some comfort advantage.
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Kenkat
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Re: HVAC simplicity vs efficiency choice

Post by Kenkat »

After having a single stage system and then replacing that with a two stage system, I would never go back to a single stage set-up. Overall evenness of temperature and comfort is noticeably better with the two stage setup. Ours is a high efficiency Bryant and we’ve had no issues so far; the system is 10 years old.

I am not familiar with Bosch A/C and not sure what Arm. is, but I would only consider option C for myself.

Edited to add: we did replace a capacitor recently on the A/C unit but this is pretty common at the 10 year point and not an expensive fix.
Last edited by Kenkat on Sat May 01, 2021 11:59 am, edited 1 time in total.
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TomatoTomahto
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Re: HVAC simplicity vs efficiency choice

Post by TomatoTomahto »

Variable speed for the comfort win.
I get the FI part but not the RE part of FIRE.
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jco
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Re: HVAC simplicity vs efficiency choice

Post by jco »

Kenkat wrote: Sat May 01, 2021 11:57 am I am not familiar with Bosch A/C and not sure what Arm. is, but I would only consider option C for myself.
Sorry. Arm. = Armstrong. I added updated this in the original post too.
Cash is King
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Re: HVAC simplicity vs efficiency choice

Post by Cash is King »

OP,

I suggest you go to this website and post your question: https://hvac-talk.com/vbb/. In my opinion, you don't need 20 seer in Colorado and you can get a 2 stage at 17-18 Seer for less money.

The other thing that's important is to ask your installer to provide you an AHRI reference number. This number means that your outdoor system (Condenser) and your indoor unit (evaporator) have been certified as a matched system. The certificate can be used In some areas to obtain rebates from utility companies. AHRI.com.

FWIW, I live in the Southwest where temps in the summer can hit 110 plus. We replaced our two 20 plus year units (in 2020) with Trane single stage 16 Seer. We have gone through one summer with the units and are very happy with comfort level and our utility bill. :mrgreen:

We did replace both furnaces as well.

Option C is a bad choice simple because you don't need a 4 or 5 ton system. My guess in Colorado a 14 Seer is the sweet spot for comfort and $$.

Cheers.

Edited to add: We did choose VS furnaces (XV80 Trane).
Last edited by Cash is King on Sat May 01, 2021 2:26 pm, edited 2 times in total.
Cash is King
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Re: HVAC simplicity vs efficiency choice

Post by Cash is King »

Choosing the best installer is more important than the brand.
teCh0010
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Re: HVAC simplicity vs efficiency choice

Post by teCh0010 »

You have three different size systems listed.

Before you pick a brand of equipment you need to pick an installer that evaluates your environmental envelope and performs a manual j calculation. Having oversized or undersized AC will negate any comfort and efficiency gains through better equipment.

I live in a high humidity warm zone that still sees winter (TN). I stuck with an 80% furnace for simplicity and reuse of my existing B vent roof penetration, but went two stage furnace and ac with a variable speed fan for comfort.
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Re: HVAC simplicity vs efficiency choice

Post by tomd37 »

jco - My understanding is that the minimum SEER these days is 14. Could this Trane unit be an older one? Maybe someone else will chime in.
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Re: HVAC simplicity vs efficiency choice

Post by Californiastate »

jebmke wrote: Sat May 01, 2021 11:51 am We went to 2-stage heat pump (variable speed fan). One advantage of the two stage system for us is that we don't get as much drafty cooling and heating since the system can run on the lower compressor stage much of the time - and the fan runs very low for longer keeping temps much more even. So, in addition to some energy savings, we get some comfort advantage.
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Re: HVAC replacement when experts disagree

Post by LadyGeek »

In order to provide appropriate advice, it's best to keep all the info in one post. I merged jco's update back into the original question, as several replies duplicate information from the earlier discussion.

I also edited the first post to let readers know about the update.
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Re: HVAC simplicity vs efficiency choice

Post by jco »

tomd37 wrote: Sat May 01, 2021 2:04 pm jco - My understanding is that the minimum SEER these days is 14. Could this Trane unit be an older one? Maybe someone else will chime in.
It's 13 SEER in Colorado.
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Re: HVAC simplicity vs efficiency choice

Post by jco »

Cash is King wrote: Sat May 01, 2021 12:30 pm Choosing the best installer is more important than the brand.
I agree with that. All of these contractors have excellent reviews. The problem is that the people reviewing them are homeowners like me who don't know what a good installation is! And every contractor insists that they are the best installer.

I'm not partial to a particular brand, which is why I didn't ask about that. Only the sizing (in the thread that his since been merged).
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Re: HVAC simplicity vs efficiency choice

Post by jco »

Cash is King wrote: Sat May 01, 2021 12:28 pm OP,

I suggest you go to this website and post your question: https://hvac-talk.com/vbb/. In my opinion, you don't need 20 seer in Colorado and you can get a 2 stage at 17-18 Seer for less money.

The other thing that's important is to ask your installer to provide you an AHRI reference number. This number means that your outdoor system (Condenser) and your indoor unit (evaporator) have been certified as a matched system. The certificate can be used In some areas to obtain rebates from utility companies. AHRI.com.

FWIW, I live in the Southwest where temps in the summer can hit 110 plus. We replaced our two 20 plus year units (in 2020) with Trane single stage 16 Seer. We have gone through one summer with the units and are very happy with comfort level and our utility bill. :mrgreen:

We did replace both furnaces as well.

Option C is a bad choice simple because you don't need a 4 or 5 ton system. My guess in Colorado a 14 Seer is the sweet spot for comfort and $$.

Cheers.

Edited to add: We did choose VS furnaces (XV80 Trane).
I don't think we need a 20 SEER system. But two contractors suggested it because of the incredible rebates our utility company is giving on the ultra-high efficiency heat pumps.

Thank you for the advice about the AHRI number. I didn't even know to ask about that.

Regarding your comment about option C, even though it's a 2-stage system, your overall opinion is that it's still oversized, so why not just get the smaller, properly sized system. It may come down to the rebate thing.
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Re: HVAC replacement when experts disagree

Post by adestefan »

I got a variable Trane 6 years ago and it’s awesome. In that time I had one sensor go bad in the heat pump that was replaced for free under warranty. Put me in column as never going back to a traditional design.
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Re: HVAC simplicity vs efficiency choice

Post by jco »

teCh0010 wrote: Sat May 01, 2021 1:39 pm You have three different size systems listed.

Before you pick a brand of equipment you need to pick an installer that evaluates your environmental envelope and performs a manual j calculation. Having oversized or undersized AC will negate any comfort and efficiency gains through better equipment.

I live in a high humidity warm zone that still sees winter (TN). I stuck with an 80% furnace for simplicity and reuse of my existing B vent roof penetration, but went two stage furnace and ac with a variable speed fan for comfort.
The hard part is that they all say they are performing the correct manual J. But the detailed one I got from one of the installers suggested we needed slightly less than 45,000 BTUs of heating and less than 25,000 BTUs of cooling. I think it's common to say that 1 ton cooling = 12,000 BTUs. A 2.5 ton cooling system would put out 30,000 BTUs of cooling. And at 80% efficiency, we'd need a 57,000 BTU furnace.
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Re: HVAC simplicity vs efficiency choice

Post by Cash is King »

jco wrote: Sat May 01, 2021 3:32 pm
Cash is King wrote: Sat May 01, 2021 12:28 pm OP,

I suggest you go to this website and post your question: https://hvac-talk.com/vbb/. In my opinion, you don't need 20 seer in Colorado and you can get a 2 stage at 17-18 Seer for less money.

The other thing that's important is to ask your installer to provide you an AHRI reference number. This number means that your outdoor system (Condenser) and your indoor unit (evaporator) have been certified as a matched system. The certificate can be used In some areas to obtain rebates from utility companies. AHRI.com.

FWIW, I live in the Southwest where temps in the summer can hit 110 plus. We replaced our two 20 plus year units (in 2020) with Trane single stage 16 Seer. We have gone through one summer with the units and are very happy with comfort level and our utility bill. :mrgreen:

We did replace both furnaces as well.

Option C is a bad choice simple because you don't need a 4 or 5 ton system. My guess in Colorado a 14 Seer is the sweet spot for comfort and $$.

Cheers.

Edited to add: We did choose VS furnaces (XV80 Trane).
I don't think we need a 20 SEER system. But two contractors suggested it because of the incredible rebates our utility company is giving on the ultra-high efficiency heat pumps.

Thank you for the advice about the AHRI number. I didn't even know to ask about that.

Regarding your comment about option C, even though it's a 2-stage system, your overall opinion is that it's still oversized, so why not just get the smaller, properly sized system. It may come down to the rebate thing.
I understand about the rebate but don't chase a rebate and end up with a system that is not properly sized. My two cents. :sharebeer
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Re: HVAC simplicity vs efficiency choice

Post by talzara »

jco wrote: Sat May 01, 2021 9:36 am My main question is whether the reliability of the higher efficiency (AFUE) furnaces is noticeably worse than the standard 80% AFUE furnaces and/or whether the maintenance costs are substantially higher? As can be seen in the table, in theory, I can get the highest efficiency system for the lowest cost after rebates! It's tempting, but if I end up having a system that breaks down all the time and lots of labor charges, then it won't be worth it. I've heard the higher AFUE furnaces are more sensitive and there are more electrical problems. Higher efficiency comes at higher complexity, so there are more points of failure.
That applies to air conditioners, not furnaces. Condensing furnaces aren't that complex. They just have a sealed combustion chamber, an inducer fan, and a secondary heat exchanger.

Modern furnaces are all controlled by circuit boards, so a non-condensing furnace can also have electrical problems.
jco wrote: Sat May 01, 2021 9:36 am Are there any additional factors I should consider here? I'm tempted to go with option C and see if I can get an extended labor warranty. It's the cheapest after rebates and the most efficient. As long as it's reliable, it seems like the clear choice. The extended warranty would be paid for by the extra efficiency over time.
Since you're worried about servicing, contractor C is the riskiest choice.

Bosch is new to the residential HVAC business in the United States. The Bosch IDS family of heat pumps just came on the market 4 years ago. It could be harder to get parts, and it will be harder to find HVAC contractors who can repair it.

It's also paired with a furnace from another manufacturer. Bosch makes a 96% furnace, but contractor C didn't select it. AHRI ratings usually pair air conditioners with furnaces from the same manufacturer. Are you sure you qualify for the rebates?
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Re: HVAC replacement when experts disagree

Post by FrugalInvestor »

The last time I replaced a system I made a concerted effort to find an HVAC company that was knowledgeable about whole house energy efficiency. The company I settled on ended up making some energy efficiency upgrades to the house (i.e. added blow-in insulation) as well as the system itself (i.e. duct sealing, duct re-routing and intake air ducting reconfiguration). As a result I ended up downsizing my tonnage and having a much more comfortable house and a quieter system, not to mention very noticeable savings on my electric bills while keeping the house cooler in the summer.

It was a real win-win but required my getting about 5 bids and asking a lot of questions in order to be comfortable that I was doing the right things. I think my DW thought that I was going a bit overboard but in the end she was very pleased because all of her concerns were desires were fulfilled. 8-)

P.S. One of the keys was also a more energy efficient system (but not going overboard with things like active zoning that add expense and complexity) with variable/multi-speed compressor and fan as I believe someone mentioned above.
Have a plan, stay the course and simplify. Then ignore the noise!
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Re: HVAC simplicity vs efficiency choice

Post by talzara »

jco wrote: Sat May 01, 2021 3:37 pm The hard part is that they all say they are performing the correct manual J. But the detailed one I got from one of the installers suggested we needed slightly less than 45,000 BTUs of heating and less than 25,000 BTUs of cooling. I think it's common to say that 1 ton cooling = 12,000 BTUs. A 2.5 ton cooling system would put out 30,000 BTUs of cooling. And at 80% efficiency, we'd need a 57,000 BTU furnace.
45,000 BTU/h of heating load for 2,900 sqft in Colorado? That's low.

I would've expected closer to 60,000 BTU/h. The Manual J design temperature for most cities in Colorado is in the single digits Fahrenheit.

What are the actual Manual J numbers? Outside temperature, inside temperature, insulation, air infiltration, internal gains, solar gains, etc.? You have three Manual Js, and the highest one is twice the lowest one. What's making them so different?
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Re: HVAC replacement when experts disagree

Post by snackdog »

I would avoid Amana and Bosch and try to get a Lennox quote.
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Re: HVAC replacement when experts disagree

Post by tibbitts »

talzara wrote: Thu Apr 29, 2021 12:41 pm
tibbitts wrote: Wed Apr 28, 2021 2:32 pm Sometimes solving all the other "little" problems that add up to making the "correct" amount of cooling just barely adequate costs a lot more than the next size hvac and the extra cost to run it for whatever the life of it is.
I replied to a post that said an "oversized" system could not keep up. It did not say that a "barely adequate" system could not keep up.

You can keep making it bigger and bigger, but the system is already oversized. It's better to solve the actual problem, even if it costs more than putting in a new system.

There are a lot of HVAC threads on Bogleheads that complain about one room, one floor, or an addition being hotter than the rest of the house. Oversizing the central air conditioner will not solve the problem. You need to add zoning dampers, more insulation, more supplies, more returns, or a mini-split.
After upsizing from 2.5t single-stage to 3t two-stage, I added adjustable dampers, more attic insulation, all new low-e windows, a new larger plenum, more returns, and enlarged the supply. It still can't keep up. Going to 4t would have been much cheaper than doing all that other stuff, although some of those items would have been necessary anyway to accommodate the required increase in airflow.
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Re: HVAC replacement when experts disagree

Post by talzara »

tibbitts wrote: Sat May 01, 2021 6:17 pm After upsizing from 2.5t single-stage to 3t two-stage, I added adjustable dampers, more attic insulation, all new low-e windows, a new larger plenum, more returns, and enlarged the supply. It still can't keep up. Going to 4t would have been much cheaper than doing all that other stuff, although some of those items would have been necessary anyway to accommodate the required increase in airflow.
You put in dampers, so you probably had uneven temperatures.

Airflow is Manual D. How much airflow did the Manual D provide, and how much airflow was measured after all the changes were made?

Manual S can treat the whole house as a block load, or it can be calculated room-by-room. When you have uneven temperatures, you need a room-by-room calculation. Then Manual D selects ductwork that will provide enough airflow to each room to heat/cool just that room.

If a room needs twice as much airflow, then adding 50% more airflow won't solve the problem. Sometimes it's easier to put in a mini-split.
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Re: HVAC replacement when experts disagree

Post by Lee_WSP »

This is the importance hierarchy

1. Availability of replacement parts
2. Ease of repair
3. Everything else
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Re: HVAC replacement when experts disagree

Post by jco »

Thank you all for your help.

We ended up going with a 3-ton, two-stage heat pump and 90K two-stage 80% AFUE furnace. The contractor provided a detailed manual J based on our desired settings. The heat pump comes with a pretty substantial rebate, so the system will cost about $10,000 after rebates. They're also performing a lot of ductwork improvement to make sure the air flows as well as possible, as well as adding some hot air returns in the upstairs (basically, cutting a return at the top of the wall to get better hot air removal during the summer). And it comes with a 10-year parts and labor warranty at a price similar to what other contractors were offering with a 2 or 3-year labor warranty. We'll have to do twice-a-year maintenance, but we should be doing that anyway.
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Re: HVAC replacement when experts disagree

Post by Normchad »

jco wrote: Mon May 03, 2021 5:01 pm Thank you all for your help.

We ended up going with a 3-ton, two-stage heat pump and 90K two-stage 80% AFUE furnace. The contractor provided a detailed manual J based on our desired settings. The heat pump comes with a pretty substantial rebate, so the system will cost about $10,000 after rebates. They're also performing a lot of ductwork improvement to make sure the air flows as well as possible, as well as adding some hot air returns in the upstairs (basically, cutting a return at the top of the wall to get better hot air removal during the summer). And it comes with a 10-year parts and labor warranty at a price similar to what other contractors were offering with a 2 or 3-year labor warranty. We'll have to do twice-a-year maintenance, but we should be doing that anyway.
Thanks for the update!

Please post back in about a year, and update us on all how well it works, how satisfied you are, and if you would have done anything differently. That info will be helpful to somebody in the future.
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Re: HVAC replacement when experts disagree

Post by tibbitts »

talzara wrote: Sun May 02, 2021 12:23 pm
tibbitts wrote: Sat May 01, 2021 6:17 pm After upsizing from 2.5t single-stage to 3t two-stage, I added adjustable dampers, more attic insulation, all new low-e windows, a new larger plenum, more returns, and enlarged the supply. It still can't keep up. Going to 4t would have been much cheaper than doing all that other stuff, although some of those items would have been necessary anyway to accommodate the required increase in airflow.
You put in dampers, so you probably had uneven temperatures.

Airflow is Manual D. How much airflow did the Manual D provide, and how much airflow was measured after all the changes were made?

Manual S can treat the whole house as a block load, or it can be calculated room-by-room. When you have uneven temperatures, you need a room-by-room calculation. Then Manual D selects ductwork that will provide enough airflow to each room to heat/cool just that room.

If a room needs twice as much airflow, then adding 50% more airflow won't solve the problem. Sometimes it's easier to put in a mini-split.
You are assuming I did all this work myself. The contractor put in dampers to provide for balancing in the future if it was required while they were replacing the plenum and replacing some ducts with larger ones. I didn't do the measurements myself, you can't seriously expect me to have all those exact values years later. The point was that originally multiple contractors threw all the Manual-whatever math at this and it was an absolute, complete, total failure. If I had to do this over I'd go 2-stage again, but with at least 25% more capacity than even the most inflated creative manipulation of Manual-whatever can come up with, as long as I had sufficient airflow for that unit.
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Re: HVAC replacement when experts disagree

Post by talzara »

tibbitts wrote: Mon May 03, 2021 5:21 pm You are assuming I did all this work myself. The contractor put in dampers to provide for balancing in the future if it was required while they were replacing the plenum and replacing some ducts with larger ones. I didn't do the measurements myself, you can't seriously expect me to have all those exact values years later. The point was that originally multiple contractors threw all the Manual-whatever math at this and it was an absolute, complete, total failure. If I had to do this over I'd go 2-stage again, but with at least 25% more capacity than even the most inflated creative manipulation of Manual-whatever can come up with, as long as I had sufficient airflow for that unit.
If you didn't keep a copy of the numbers, how will you know if the next HVAC contractor did it right? "Multiple contractors" made the same mistake last time.

Since you have a problem with uneven temperatures, a larger air conditioner will not solve it. The relative airflow to each room will not change. Maybe you're planning to use an oversized air conditioner to overcool the coldest room so that the hottest room becomes more comfortable. That is just trading one problem for another.

Manual J really works. The physics of heat transfer are well-understood. The problem is that HVAC contractors are typing numbers into software, and they don't make money from doing the most accurate Manual J calculation. They only make money when they sell you an HVAC system.

The OP got three contractors to do the Manual J calculation, and they came out at 2.5 tons, 3 tons, and 4 tons. They can't all be correct.
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Re: HVAC replacement when experts disagree

Post by tibbitts »

talzara wrote: Tue May 04, 2021 1:59 pm
tibbitts wrote: Mon May 03, 2021 5:21 pm You are assuming I did all this work myself. The contractor put in dampers to provide for balancing in the future if it was required while they were replacing the plenum and replacing some ducts with larger ones. I didn't do the measurements myself, you can't seriously expect me to have all those exact values years later. The point was that originally multiple contractors threw all the Manual-whatever math at this and it was an absolute, complete, total failure. If I had to do this over I'd go 2-stage again, but with at least 25% more capacity than even the most inflated creative manipulation of Manual-whatever can come up with, as long as I had sufficient airflow for that unit.
If you didn't keep a copy of the numbers, how will you know if the next HVAC contractor did it right? "Multiple contractors" made the same mistake last time.

Since you have a problem with uneven temperatures, a larger air conditioner will not solve it. The relative airflow to each room will not change. Maybe you're planning to use an oversized air conditioner to overcool the coldest room so that the hottest room becomes more comfortable. That is just trading one problem for another.

Manual J really works. The physics of heat transfer are well-understood. The problem is that HVAC contractors are typing numbers into software, and they don't make money from doing the most accurate Manual J calculation. They only make money when they sell you an HVAC system.

The OP got three contractors to do the Manual J calculation, and they came out at 2.5 tons, 3 tons, and 4 tons. They can't all be correct.
After the ductwork upgrade several years ago the rooms are reasonably well balanced, whereas they weren't before. They aren't balanced the same under every environmental condition: sunlight (or lack thereof) has considerable effect for example. In theory self-adjusting dampers using sensors could resolve that, but perfect balance is not important to me. Now that I have experience with the house and the various upgrades (windows, insulation, etc.) that have been made, there would be no benefit to doing any more calculations, especially since in my case all the contractors arrived at the same conclusion. Even if my unit was perfectly sized, I'd still have the problem of the unit not operating at all during the hottest hours of the day, and then wanting it to cool the house rapidly after that. I don't believe a theoretically perfectly sized/balanced/whatever unit would be the best at accomplishing that.
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