New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

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RetireSoon90
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New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by RetireSoon90 » Thu Mar 14, 2019 4:00 am

I just got a new Trio Oil Boiler by PurePro with a Vaughn Indirect Hot Water Heater installed. We have baseboard heating. We always turn the house thermostat down to 60 at night to save on oil/money. The installers said that turning down the thermostat does not save money because when I turn the heat up to 66 in the morning the boiler needs to run for an hour to get the house temperature back up to 66. We live in the Northeast. The boiler is set to 160, which is what the installers set it at and I would rather not adjust :)

Does turning the house thermostat down at night save on burning oil/money? How low does everyone typically turn their thermostat down to at night? Thanks!
Last edited by RetireSoon90 on Thu Mar 14, 2019 7:36 am, edited 6 times in total.

Valuethinker
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Re: New Oil Boiler/Indirect Hot Water Heater - Turn Temperature Down at Night?

Post by Valuethinker » Thu Mar 14, 2019 4:58 am

[repeated]
Last edited by Valuethinker on Thu Mar 14, 2019 5:01 am, edited 1 time in total.

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn Temperature Down at Night?

Post by Valuethinker » Thu Mar 14, 2019 5:00 am

Valuethinker wrote:
Thu Mar 14, 2019 4:58 am
RetireSoon90 wrote:
Thu Mar 14, 2019 4:00 am
I just got a new Trio Boiler by PurePro with a Vaughn Indirect Hot Water Heater installed. We always turned the heat down to 60 at night to save on oil/money. The installers said that turning down the heat does not save money because the when I turn the heat up to 66 in the morning the boiler needs to run for an hour to get the temperature back up to 66. We live in the Northeast.

Does turning the heat down at night save on burning oil/money? Also how low does everyone typically turn the heat down to at night? Thanks!
I shall be interested to see if the energy gurus around here agree with me.

The amount of energy used is basically driven by: target temperature (how much of an increase from ambient) + hours running. There is a factor about efficiency - boilers need a long run to be maximally efficient, rather than on-off. Modern boilers usually "modulate" ie they can then step down from full output which makes this less of a problem.

Thus, turning the heat down will probably save you money. Because the boiler runs for fewer hours - the key number is the gap between desired temperature and ambient (inside air temperature which is modulated by how much insulation you have, how airleak tight your house is, what other heat is generated by people & appliances).

The hour run in the morning will be at full efficiency (could be over 90% depending on the boiler). And that heat has less time to leak out of the hot water tank and/or the house before you need it.

I am assuming your 60 F and 66 F are for the heating the system produces? As a hot water temperature 66 F is very low - it's not really hot water.


FWIW my boiler (with a 45 US gallon tank) kicks in at 530 am and runs for 2 hours to provide enough HW for 2 people. Runs again then 430-630 pm -- probably I could do without that, but just in case there's a lot of hot water being used. The tank is super-insulated though (factory installed foam insulation).

Input water temperature for me is around 10 degrees C all year round but output is required to be 65-70 degrees C by law due to concerns about Legionnaire's Disease (which is actually a problem at the shower end not at the hot water tank 3 floors away).

BTW with heat pumps it's different - they run at lower temperature output and so "long and slow" is more efficient (the efficiency is the inverse of the gap between input and output temperature. They work well with underfloor hot water heating for example.

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RetireSoon90
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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by RetireSoon90 » Thu Mar 14, 2019 5:07 am

I turn the House temperature down to 60 at night and 66 in the morning. Looks like the boiler is set at 160, I don't really want to modify what the installers set it at :)

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by Valuethinker » Thu Mar 14, 2019 5:23 am

RetireSoon90 wrote:
Thu Mar 14, 2019 5:07 am
I turn the House temperature down to 60 at night and 66 in the morning. Looks like the boiler is set at 160, I don't really want to modify what the installers set it at :)
1. no I would not change the boiler setting - there's a health & safety issue, and I don't know what your local code says

2. if you turn down the thermostat for the heating, you use less energy. Getting the house back up to day temperature won't burn more energy than keeping it at the higher temperature over time and you won't lose it over those night hours (heating the house only to lose heat to the outside air and ground). So you are saving yourself money.

The installer either does not know what he/she is talking about, or somehow the conversation wires got crossed - a misunderstanding.

The main thing for most people is they want the heat to come on up to an hour before they get up, so the house is warm then.

(the advice if one had a heat pump would be different, possibly).

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by mmmodem » Thu Mar 14, 2019 6:17 am

I'm not an expert. I would like to hear from an expert but until I do, I'm with valuethinker. We also have a indirect hot water oil burner. We keep the bedroom at 62 degrees and the rest of the home at 50. We turn up the rest of the home to 60 when we wake up.

I've never checked the temperature of the boiler. I don't know if there is one. The hot water heater was set at 140 default and I turned it down to 120. The reason I can think of that the installers recommend 140 (disease and local area codes not withstanding) is because it will take longer to hot water heat a home at 120 than at 140. I can imagine their customers would be very irate if after an hour, their home is still not up to temperature. I don't mind this as you can set smart thermostats to start heating a home earlier than you need it so it's at the temperature you want.

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by RickBoglehead » Thu Mar 14, 2019 6:23 am

I don't believe the hot water temperature has anything to do with heating the home. It's the temp that the hot water is heated to. Turning it down can prevent a scalding incident, especially with young children.

However, one should pull the manual for their dishwasher. To properly sanitize dishes, a dishwasher may heat the water to a specific temperature. That heating of the water may use a lot of electrical energy. Having water at 120 that has to be heated to 155 vs. water at 140 that has to be heated to 155.

When I read about people keeping their living spaces at 60 degrees during the day, I can't imagine doing that. We turn our house down to 65 at night and it's 70 during the day. However, I note a difference between a house with forced hot air heat and a house with hot water baseboard heat as far as how warm or cold the house feels. Humidity levels also impact the feel of the temperature.
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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by onourway » Thu Mar 14, 2019 6:43 am

I don’t know if this is how your system works, but our high efficiency boiler is intended to leave the home set at one temperature at all times. The boiler has a connection to an outdoor thermo-probe, and it uses an efficiency curve to determine what temperature to heat the water in the boiler based on the outside temperature. If you turn the thermostat down at night as I was used to, it would take up to 12 hours to reach the day-time temperature again! I complained about this to our installer, whose suggestion was to unplug the thermo-probe and crank up the boiler temp manually! Clearly that was not how it was intended to work (although it would make it work the way I thought I wanted it to) but I was curious enough to dig into it myself. Much of the efficiency of this design comes from the fact that it circulates relatively low-temperature water through the pipes most of the time, with the boiler operating at a very low output, rather than pumping very hot water through the pipes in short bursts.

It was a bit of an adjustment to get used to sleeping in the warmer temperature, but now I wouldn’t have it any other way because the entire house is now permanently the ideal temperature. There is no drastic temperature swing every day where the radiators are heating up, but the house ‘feels’ cold because the rest of the mass of the place is cold-soaked.

It sounds like your system might be intended to work the same way. Or your guys also don’t know what they are talking about and you’ll have to figure it out yourself. :D Does the boiler always run at 160 for heat, or does it vary?

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RetireSoon90
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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by RetireSoon90 » Thu Mar 14, 2019 7:13 am

The boiler always runs at 160 and we do not have an outdoor thermo-probe :) It is a standard Cast Iron Boiler :)

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by Valuethinker » Thu Mar 14, 2019 7:33 am

mmmodem wrote:
Thu Mar 14, 2019 6:17 am
I'm not an expert. I would like to hear from an expert but until I do, I'm with valuethinker. We also have a indirect hot water oil burner. We keep the bedroom at 62 degrees and the rest of the home at 50. We turn up the rest of the home to 60 when we wake up.

I've never checked the temperature of the boiler. I don't know if there is one. The hot water heater was set at 140 default and I turned it down to 120. The reason I can think of that the installers recommend 140 (disease and local area codes not withstanding) is because it will take longer to hot water heat a home at 120 than at 140. I can imagine their customers would be very irate if after an hour, their home is still not up to temperature. I don't mind this as you can set smart thermostats to start heating a home earlier than you need it so it's at the temperature you want.
In an indirect system the hot water temperature for washing & cooking is a different circuit than the rads.

What's in your rads it depends. Older homes in the North East sometimes have steam radiators rather than hot water. Standard UK temperature is c. 65 degrees (150 F) (? I think?) however a heat pump would run efficiently on more like 45 C.

The OP could have hot water (indirect) and forced air for heating. North American homes tend not to have radiators (hydronic heating?) unless older and northeastern.

We are talking here about the hot water temperature - it's then mixed with cold water before it comes out of the faucet.

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by RetireSoon90 » Thu Mar 14, 2019 7:36 am

We have baseboard heating :)

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by lthenderson » Thu Mar 14, 2019 7:48 am

RetireSoon90 wrote:
Thu Mar 14, 2019 4:00 am
Does turning the house thermostat down at night save on burning oil/money?
The correct answer is that it depends on your house type. Heat transfer depends on how fast it occurs between the inside and outside of your house. If your house is conventionally stick built and insulated, heat transfer occurs quickly when compared to say a house with thick adobe walls. The faster the heat transfer occurs, the more money you will save by turning the thermostat down at night.

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by TLC1957 » Thu Mar 14, 2019 7:48 am

I had a gas fired boiler for 28 years in a 3200 sq ft home in NJ with 4 zones, 1 zone for an indirect hot water tank for domestic hot water the rest to heat the home. The domestic tank was set at 125F. The boiler water temperature was set at 180 F however when we had very cold weather, a week of 0 F I increased the boiler temperature to 200F. If I did not increase the boiler temp the house would not get above 66 F. The 3 heating zones were turned down to 60F during the day and to 68F when we were home. The zones were split as follows one zone being the 1st floor, 2nd floor 3 bedrooms on one zone and master suite on another.

The boiler temperature settings were advised by the service folks and it worked well for us.

https://www.weil-mclain.com/faq

The following is from Weil-McLain web site on boiler temperature. Perhaps contact the boiler manufacturer to see what they say, but I believe these temperatures are standard in the industry.

The average setting for the aquastat (the temperature control device on a boiler) for a forced hot water system is 180°F. It can be raised as high as 210°F if needed in severe weather. For systems that use coils to heat domestic hot water, the high limit setting is 210°F and the low limit setting 140°F. A differential setting of 15°F is recommended for the optimum amount of domestic hot water.

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by RetireSoon90 » Thu Mar 14, 2019 7:54 am

Thanks! Does turning the house thermostat down at night save on burning oil/money? How low does everyone typically turn their thermostat down to at night?

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by TheGreyingDuke » Thu Mar 14, 2019 8:00 am

To clarify, the water that the boiler circulates is, as stated, 160 F, that is NOT the temperature of the domestic hot water, such a temp would be very dangerous. The 160-degree water is circulated in a coil that is located in the separate domestic hot water tank. It should be heating that water to about 120 degrees.
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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by jharkin » Thu Mar 14, 2019 8:26 am

I just skimmed the thread so apologies in advance if this is duplicate:

#1 - Best bet is to ask these questions on the heatinghelp.com forum and get answers from some of hte HVAC pro's that post there.

https://forum.heatinghelp.com/

#2 - There should be two aquastats in the system. T indirect tank has an aquastat with a high cutoff and a differential - this will be set to whatever you want your faucet temp to be - say 120F.

#2b - The boiler has an aquastat as well - which is the one you where probably told was set to 160F. This aquastat is a high cutoff that controls how hot the boiler gets when delivering heat. In the old days 180F was common, but if the installer recommended 160 and the house heats properly on a design day (typically 0F outside) then leave it alone.

#3 The indirect water heater is treated like a "zone" the same as any heat zone of baseboards controlled by a thermostat. The indirect has its own pipe loop feeding it from the boiler with a circulator pump. Keep in mind the the water in the boiler and the indirect DO NOT MIX, the boiler water is just used in a heat exchanger to heat the hot water. So there is NO HEALTH OR HEATING CODE REQUIREMENT to maintain a constant hot temp on the boiler side. The boiler can safely go cold when neither the water heat or radiators are calling for heat.

#3 - Since you have an indirect, the boiler should have multi-zone control - both the indirect water heater and the thermostat(s) are zones and any of them can call for the boiler to fire and deliver heat. There is a priority ordering of the zones and the water heater should be setup for 1st priority - this means that if both the water heater and the TStat are calling, the Tstat zone(s) (and the circulator pump(s) for the baseboards) are put on hold and wait until the indirect water heater tank stops calling for heat .

So basically how it works is this - there are two control loops to activate the system - the zone control (triggered by indirect or tstat(s) ) and the boiler aquastat (triggered by boiler water temperature):
* If the zone control is ON and the Aquastat is ON (< 160F) - burner ON and circulator(s) ON
* If the zone control is ON and the Aquastat is OFF (>= 160F) - burner OFF and circulator(s) ON
* If the zone control is OFF - burner OFF and circulators OFF


To answer your questions:

YES it is absolutely fine to set the thermostat back to 60F at night. This will not damage anything and the length of time to heat back up to 66 in the morning does not use more fuel than just leaving the house warm all night. That's an urban legend that has been debunked. Of course your installer tries to tell you it doesn't work, because they are probably also the people selling you oil :oops:

https://blog.powerley.com/mythbuster-us ... y-savings/
http://www.homeenergy.org/show/article/id/566


NO the boiler should not be setup to just maintain 160F 24 hours a day. That's a holdover from the days when boilers with instant hot water coils where common. Idling the boiler at 160F with an indirect is an unnecessary waste of energy. The water heater stays warm from its insulation jacket and will just call for heat as needed.

Again this is something the installer may push back on because having the boiler run constantly lets them sell you more oil. Buyer beware....

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by Valuethinker » Thu Mar 14, 2019 11:05 am

RetireSoon90 wrote:
Thu Mar 14, 2019 7:54 am
Thanks! Does turning the house thermostat down at night save on burning oil/money? How low does everyone typically turn their thermostat down to at night?
1. if your electric baseboards come on then it is almost certainly *not* saving you money (exception: if it is only baseboards in the 1 bedroom). Compared to oil, baseboard heating would typically cost say 3x as much for the same amount of heat (somewhere between 2.5 and 5 times).

2. otherwise yes turning it down at night will save you money.

It's about health. The research says we sleep better with lower temperatures. We also probably burn a few more calories.

But there is a lower threshold beyond which this is counterproductive. It may vary by country and person (probably does) but I would suggest it's something like 58 to 60 F. And as we get older, like my cat, we need a warmer environment. People with health problems often do as well.

66 seems cold for a home in winter in the daytime, to be honest.
Last edited by Valuethinker on Thu Mar 14, 2019 12:01 pm, edited 1 time in total.

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by adamthesmythe » Thu Mar 14, 2019 11:44 am

You will ALWAYS save money by turning down the temperature at night. HOW MUCH depends on details of heat loss from the house. If the house temperature drops very rapidly then you will save a lot. (But, then you would also save a lot by improving insulation).

Deciding how much to turn it down is a tradeoff between comfort and cost.

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by PVW » Thu Mar 14, 2019 11:55 am

I have an older (maybe 30 year old) cast iron boiler for hydronic radiators. 1 zone, no indirect hotwater heater. My HVAC technician told me that boilers like constant thermostat settings. His reasoning was that when heating a house from a cool state, the water is colder than normal and the boiler will fire for longer than normal and this causes excessive condensation in the cast iron heat exchanger, causing rust.

I haven't done any further investigation, so I can't comment on the accuracy of this, but I do leave my thermostat at a constant temperature. Part of the reason is that with single zone heating, when heating up, the house isn't at thermal equilibrium when the thermostat comes up to temperature and I feel a cold draft coming from upstairs.

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by Spirit Rider » Thu Mar 14, 2019 8:50 pm

This is a matter of simple physics and boiler efficiency. The fact that the installers would be this ignorant would cause me to go to a different company for future servicing.

The amount of BTUs necessary to heat a given house at a given temperature will be based on heat loss dynamics of the house (shape, insulation, etc...). Once that is established actual BTUs over a given period of time will be based on time and the temperature differential between the inside and the outside. The lower the temperature inside overnight the lower the BTU requirement to maintain that temperature.

Now when you the temperature is raised the next morning that will require an increase in BTUs required to bring the temperature back up. This is compounded by the fact that the morning tends to have the lower temperatures of the day and there is the houses mass that has cooled overnight. This will necessitate a significant increase in the duty cycle of the burner. People notice this and assume that because the burner is running a lot to get the temperature raised back up it is inefficient. However, the burner is actually at its most efficient when it is running more continually and not starting and stopping. The fuel savings is based on amount time vs. the temperature differential. It is a mathematical model.

The one exception to this general rule of setting back the thermostat is with the manual operation of heat pump thermostats. Typically when the difference between the ambient temperature and the thermostat setting is < a 2 degree differential the system will operate in heat pump mode which is typically 2 - 3 times more efficient that resistance heating. However, when you manually set the thermostat > 2 degrees above ambient, it will call for auxiliary resistance heating which is far more inefficient. So manually setting your heat pump thermostat to 60 degrees at night and 70 degrees in the morning will actually cost you more than leaving the setting at 70 all night. Fortunately, all modern programmable thermostats with heat pump capability will only raise the call for increased temperature incrementally and not turn on the auxiliary resistance heat. Many will learn current conditions and will start to raise the temperature to reach the temperature at the desired time.

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Re: New Oil Boiler/Indirect Hot Water Heater - Turn House Temperature Down at Night?

Post by NibbanaBanana » Thu Mar 14, 2019 9:06 pm

RetireSoon90 wrote:
Thu Mar 14, 2019 4:00 am
Does turning the house thermostat down at night save on burning oil/money? How low does everyone typically turn their thermostat down to at night? Thanks!
What you've been told seems to be a common myth among plumbers.

The answer is turning the heat down any time for any amount of time will save energy. It is a simple consequence of Newton's Law of Cooling; The rate of heat transfer is proportional to the temperature gradient.

Don't change any settings on your boiler though.

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