# Setback thermostats



## DBNH22 (Nov 10, 2013)

There's a lot of debate as to whether or not the use of setback thermostats actually saves money on heating costs.  I have them in my home but haven't used the setback feature.  We never leave the home for extended periods of time and it just seems wasteful to drop the temp while we're at work during the day onyl to have to make the boiler work to bring it back up to temp when we get home.

What does everyone else think?


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## heat seeker (Nov 10, 2013)

I think the only savings result because the lower temperature causes a lower rate of heat loss. IMO, the savings are real, but minimal.


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## fbelec (Nov 11, 2013)

there is savings but only if used right. i have talked with many boiler company's and they all say the same thing. set back to 5 degrees for the best savings. any more and it starts going in the opposite direction. some people turn down their thermostats to 55 when they leave in the morning then to 68 or 70 when they get home and they are the biggest complainers of the heat bill. the thing with heating the house back up from a low temp is yes you have to heat the air but the walls are still cold and it takes time to bring the walls up also. last apartment i rented years ago when oil was around 1:10 a gallon it was costing me about 100 a month to heat the 1100 square ft house i took off 30 a month with a set back thermostat. no difference in my setting of temp when i was home but dropped 5 degrees during the day when i was at work.


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## heat seeker (Nov 11, 2013)

Granted, you have to heat the walls and furniture back up, but they also give off heat when the thermostat goes down. It's like a flywheel effect. And not good for pianos and other temperature sensitive items.


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## DBNH22 (Nov 11, 2013)

fbelec said:


> there is savings but only if used right. i have talked with many boiler company's and they all say the same thing. set back to 5 degrees for the best savings. any more and it starts going in the opposite direction. some people turn down their thermostats to 55 when they leave in the morning then to 68 or 70 when they get home and they are the biggest complainers of the heat bill. the thing with heating the house back up from a low temp is yes you have to heat the air but the walls are still cold and it takes time to bring the walls up also. last apartment i rented years ago when oil was around 1:10 a gallon it was costing me about 100 a month to heat the 1100 square ft house i took off 30 a month with a set back thermostat. no difference in my setting of temp when i was home but dropped 5 degrees during the day when i was at work.




So do you think a setback of five degrees is a general rule of thumb?  Each home has it's own unique variables as far as the heating system, insulation, items in the house etc etc  I've always thought that turning it down even a few degrees during the day would not save money as the energy needed to bring the home back up to temp when you get home would be so great  that it would negate the savings.  Instead I have been focusing on on the overall heat loss of the home which basically means I've been trying to improve the air sealing and insulation as much as possible throughout the entire home.  Regardless of what the temp is set at your home is going to be more energy efficient (from a heating/cooling standpoint)if you keep the cold air and drafts out and the warm air in or vice versa in the summer.  It's a shame that so many people are not aware of many of the small cost-effective things that they can do to decrease their home's energy costs.


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## heat seeker (Nov 11, 2013)

Dana B said:


> would not save money as the energy needed to bring the home back up to temp when you get home would be so great  that it would negate the savings.


Don't overlook the flywheel effect that I mentioned. Everything gives off heat as house cools, so the heat is not lost, but will be replaced when the house warms up.


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## maple1 (Nov 11, 2013)

heat seeker said:


> Don't overlook the flywheel effect that I mentioned. Everything gives off heat as house cools, so the heat is not lost, but will be replaced when the house warms up.


 

Yes, but I don't think there is much if any energy savings from the flywheel.

We have setback stats, they set back at different times, but only by a degree or two. That is not to save energy directly, but to time the heat load to burning times better. They all bump up within an hour or so of each other, around supper time - just about the time I have the wood fire up to full burn. That keeps the house fairly warm during the day without drawing my heat storage down too far. If I'm home all day, I usually turn the stats back up manually so they're at 21c all day & stop feeding the fire a bit earlier in the day.

With my old oil/wood boiler, they used to get set back a bit further to try to get me thru the day without turning on the oil boiler - the sound of that thing kicking in was like nails on a chalkboard. But it took a lot of fire tending to get caught back up to temp in the evening, and I was usually up later at night & earlier in the morning than I wanted to be doing it. Thank god those days are over.


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## heat seeker (Nov 11, 2013)

maple1 said:


> Yes, but I don't think there is much if any energy savings from the flywheel.



I totally agree, and was just pointing out that, in theory, at least, the house and furnishings heating up and cooling down has no effect on heat savings. The heat used to warm the objects is released when the rooms cool.


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## mass_burner (Nov 11, 2013)

in the common areas of the house we keep our heat set for 68d. it has an automatic step down motion sensor of 2d every 15 minutes down to 62d if no one walks past it after 1/2 hour.  

my wife and i have a simple arrangement. if i keep the stoves running, the thermostat never hits 68, and the oil burner doesn't come on. if i don't run the stoves, oil burner comes on. the bedrooms are a different story.

i think the holy grail is trying to keep every BTU for as long as you can through air sealing/insulation.


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## begreen (Nov 11, 2013)

It depends on the heating system and it's recovery time. High output systems like oil and gas furnaces can see a significant savings with a setback thermostat as long as the set back isn't too radical. 5 degrees is usually plenty. We had a setback thermostat wired to our pellet stove several years ago and it was great. Lower output systems like in-floor hot water and heat pump don't benefit much. We just do a 3 degree setback with our heatpump, mostly for cooler sleeping temps.


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## RichVT (Nov 11, 2013)

I used to do energy audits for many years back when the utilities were required to offer them to their customers. Our rule of thumb was that you'll save one percent (of your heating bill) for each degree of setback for an 8 hour period. 10 degrees is an acceptable amount to set back.

Heating systems are generally less efficient when they cycle on and off so running them in one shot to heat the house back up is better than having them go on and off to maintain the higher temp.


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## DBNH22 (Nov 11, 2013)

mass_burner said:


> in the common areas of the house we keep our heat set for 68d. it has an automatic step down motion sensor of 2d every 15 minutes down to 62d if no one walks past it after 1/2 hour.
> 
> my wife and i have a simple arrangement. if i keep the stoves running, the thermostat never hits 68, and the oil burner doesn't come on. if i don't run the stoves, oil burner comes on. the bedrooms are a different story.
> *i think the holy grail is trying to keep every BTU for as long as you can through air sealing/insulation*.




I agree with you regarding the holy grail.  I was speaking with someone who lives in MA recently who had a super insulated home built a few years back.  He said that his home is a three story colonial and almost 5000 square feet.  He uses natural gas to heat which we all know is as cheap as it gets for heating.  I was still shocked when he said he only spends about $50 dollars or so a month to heat his home.  When done properly and thoroughly insulation and air sealing can provide phenomenal savings on heating/cooling costs.  I think most of us that aren't millionaires living in custom built super insulated homes find that the contractors that built our homes did not put much effort into the home.  Typically we see fiberglass batts thrown here and there, installed improperly and very inefficient.  It's all about getting the job done as quickly and cheaply as possible and then moving on to the next house.


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## woodgeek (Nov 11, 2013)

RichVT nailed it.  For an 8 hour setback, 1% savings per degree.  If you have a HP, don't set back, otherwise an easy way to save 5-10%.

Edit: I should have said, if you have a HP, be careful setting back, you only save $$ if it doesn't call aux on recovery.


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## fbelec (Nov 11, 2013)

and radiant in floor heat you don't want to set back. i've been wiring these in floor radiant with a set that runs off the mixing valve. it regulates the water temp for the radiant by the temp outside and max temp for the floor is 110 degrees. boiler hardly runs. if one doesn't believe that a set back can save, buy one hook it up and try it for a month. for basic set back t stat cost is 39 dollars see how it does. honeywell makes one for those tstats near doors. every time the door is opened the heat comes on. they have one out that takes it's reading from the air temp and the wall temp. so if you open the door and the air temps drops for a minute or so the heat doesn't come on. but if the air and wall temp drop the heat comes up.


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## flyingcow (Nov 14, 2013)

set back works well for me. the big savings was because the family wouldn't remember all the time to turn the t-stat down when going to bed or off to work. I saw a savings in wood.


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## semipro (Nov 15, 2013)

woodgeek said:


> If you have a HP, don't set back


This statement may be overly broad.  Perhaps you're referring to systems where setback use results in emergency heat operation?
Our setback thermostat allows heat pump operation without emergency (resistive) electric operation and
has a learning mode that uses past HP performance to determine when the HP should come on to meet the preset time/temp requirements.

Edit: Our thermostat is not new tech by any means.  Its not  a Nest or something similar.  Its at least 10 years old.


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## woodgeek (Nov 15, 2013)

One CAN do setbacks on HPs, but you have to keep an eye on whether the aux is getting called during recovery.  That in turn will depend on outside temp in the morning relative to your house load and HP size.  IN milder weather it makes total sense. I do modest (4°) setbacks with my heat pump, more for sleeping comfort, while not freezing my geriatric pets than for energy savings.

And, O irony of ironies, I DO have a nest stat.  It bills itself as having very nice proprietary tech that looks at local weather forecasts to determine an optimum setback temp (if the evening is warm and morning is cold, the COP will be lower on recovery and it can (hypothetically) make sense to not set back sometimes).

In 18 mos of use, I would say it doesn't work worth chit.  When I engage the fancy algos, they call aux way more than my old stat would, and when it clearly isn't needed (e.g. 45° outside).  So defective that IMO their savings claims for HPs constitute false advertising, and a potential class-action lawsuit liability.  Why do I keep using it, despite it costing me $50-100 per season in _extra_ energy?  The usage logging function is useful to me, and nest will presumably fix it and update the software at some point.


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## fbelec (Nov 16, 2013)

woodgeek if it's costing you money to run the nest what's the point. i've had only two installs of the nest and never got any feedback. i think if i were you for what you need a set back for i would put in a simple setback that won't turn on the aux heat. i'm not sure if they still make the clock type because of the mercury switches but that type would work for you without the aux heat. on those old tstats it was manual switch for aux heat. i just did a heat pump install with dual fuel. heat pump and gas backup with a focus pro tstat. i don't remember if you could block out the aux heat but it was a very nice tstat with wifi built in. you don't even have to get out of the chair to adjust the temp. just use the computer.


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## woodgeek (Nov 16, 2013)

I'm using it for the energy usage logging function, which has been useful to me through a series of energy eff improvements.  I previously used a HW Visionpro for several years, and it was perfect (but not internet connected or logging).  I can always return to that if I give up on the Nest.

In practice I turn off the fancy stuff, and do a setback. The main remaining problem is that the min aux lockout temp is 35°F, and I never need aux above 25.  So I tell the unit I live in WashDC, where it runs 7-10°F warmer than my location, to simulate that effect, and my extra usage is only about 5% of total.

Bottom line, its a 'beta' product, still after 2 years on the market. I think it is aok for single stage heat/cool systems, but the multistage control is incorrect/badly programmed. It will be a great product after the kinks are worked out.


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## velvetfoot (Nov 16, 2013)

Getting a little off topic, but now with burning wood, I don't do setback at all.  We have them, but they both are on something like 50.  We do have an ecobee internet thermostat, that like the nest, can track usage and temps, also turning up the heat remotely is nice.  Although, last time we came back from vacation that feature didn't work.  The router, which is connected to a cellular modem (no cable, etc, here, and I think the cellular/router combo is to blame), needed rebooting.


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## DBNH22 (Nov 18, 2013)

velvetfoot said:


> Getting a little off topic, but now with burning wood, I don't do setback at all.  We have them, but they both are on something like 50.  We do have an ecobee internet thermostat, that like the nest, can track usage and temps, also turning up the heat remotely is nice.  Although, last time we came back from vacation that feature didn't work.  The router, which is connected to a cellular modem (no cable, etc, here, and I think the cellular/router combo is to blame), needed rebooting.




I have glanced at the ecobee website in the past and I know their products are not cheap.  How robust is the ecobee software?  Does it track all the calls for heat during the day?  I have a pellet boiler that is controlled by fairly sophisticated software but it does not have the ability to generate reports and statistics with regard to how it is performing.  I'm trying to find some way to objectively track how the heating system is performign and whether or not things like temp setbacks are actually resulting in a more efficient use of energy in my home.


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## Seasoned Oak (Nov 18, 2013)

I just put the wood in the stove and "set back" an enjoy the heat.


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## velvetfoot (Nov 18, 2013)

Dana B said:


> I have glanced at the ecobee website in the past and I know their products are not cheap.  How robust is the ecobee software?  Does it track all the calls for heat during the day?  I have a pellet boiler that is controlled by fairly sophisticated software but it does not have the ability to generate reports and statistics with regard to how it is performing.  I'm trying to find some way to objectively track how the heating system is performign and whether or not things like temp setbacks are actually resulting in a more efficient use of energy in my home.



It graphs runtime as well as weather adjusted runtime, not that I use that feature that much.
It also graphs stuff like interior temperature, outside temperature and humidity (as reported by the web-I have the cheaper unit without outside temp input), humidity and desired heat.  I just looked at my chart, and it seems that my wife loaded the stove around 8:30 AM.


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## jdp1152 (Dec 8, 2013)

One can't simply assign a value where the crossover occurs. Different systems and home layouts will yield ver different results.


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## fbelec (Dec 8, 2013)

jdp1152 said:


> One can't simply assign a value where the crossover occurs. Different systems and home layouts will yield ver different results.



what do you mean?


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## jdp1152 (Dec 8, 2013)

fbelec said:


> what do you mean?



Entirely too many variables to say with certainty that X degree setback is detrimental or beneficial to everyone. It's going to depend on how efficiently you maintain temps ( insulation, air leakage, solar gain, type of structure retaining thermal mass , etc) as well as how efficiently you can rebuild those temps.  Your house and your heating system will determine what level, if any, you should set back to save, if any, money.  There is no one size that fits all and any HVAC person who states otherwise should know better.


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## fbelec (Dec 9, 2013)

jdp1152 said:


> Entirely too many variables to say with certainty that X degree setback is detrimental or beneficial to everyone. It's going to depend on how efficiently you maintain temps ( insulation, air leakage, solar gain, type of structure retaining thermal mass , etc) as well as how efficiently you can rebuild those temps.  Your house and your heating system will determine what level, if any, you should set back to save, if any, money.  There is no one size that fits all and any HVAC person who states otherwise should know better.



but it does take a certain amount of energy to heat the air and the walls and the furniture and a cold wood stove. yep it's a percentage. depending on what yer heating. how many square feet. no one said any dollar amount but the fact is it does and should be a certain percentage which might be slightly different money wise but with the way the majority of heating systems are designed the thermostat and boiler companys will give you the number in degrees which is what we're dealing with that is what you can gauge yer set back point if you find that your house is only 4 thats great. if you find your house saves more at ten great. it's just a gauge to go by. lots of people shut their thermostat down manually or with a setback but look at how hard it has to work to bring that temp back. 

just passing on info from what i received from those companys


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## firebroad (Dec 10, 2013)

In my experience with heating oil, I found that setting the therm back in the morning before I left (5:30) to 62, then having it come back to 67 when I returned at 5:00 then shutting it back to 62 when I went to bed until 4:30 or so did save me money; I have a reasonably insulated home; and I had a programable stat that ramps up slowly as it learns my habits.
This part is key.  Even now that I ditched oil and got a heat pump, I still use the same programming, and have found that the aux heat doesn't usually come on unless it's pretty cold outside.  The stove, of course, takes up most of the slack, so my heating system is basically the back up for my stove, and not the other way round.


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## Adios Pantalones (Dec 10, 2013)

"Building back heat" in walls etc, is not a net loss. If you had kept the temp turned up- the walls would still be losing heat (at a higher rate, as it relates to the DIFFERENCE in temp inside and out), but it would be replaced constantly by your heating system.

Your house does not magically stop losing heat just because your boiler is running.

Temp swings may be bad for some stuff in your house, and may overwork a boiler (I guess), but the thermodynamics of this are pretty clear.


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## semipro (Dec 10, 2013)

I think there may be some confusion on why setting back may save energy. 
Heat loss from your house to the outdoors occurs faster when the temp difference between outside and inside is higher. 
Therefore, lower thermostat settings result in less heat loss when its colder outside. 
However, overall setback energy savings are predicated on the fact that your heating system operates at the same (or greater) efficiency when maintaining:

+/- 5 degrees on longer cycles (setback mode). when compared to 

+/-  1 degrees on short cycles (normal thermostat mode) 
(This is a conceptual comparison for simplification. During setback your thermostat will still be cycling to maintain +/- 1 degrees though at a lower set temp).  

I can't see where solar gain, thermal mass, other factors mentioned would impact one these modes more than the other.  Solar gain would seem to occur independent of setback.  Thermal mass may create a time lag between setback time and HVAC operation but the operating time would be the same just delayed with higher thermal mass.  

Additional setback energy savings occur because most HVAC systems operate more efficiently at a steady state rather than cycling on and off often. The same start/stop inefficiencies that occur in other motors also apply to compressor and fan motors in HVAC systems. 

ORNL has done some interesting research on setting back.  They even went so far as to build different houses and then compared the energy usage using setback and not.


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## firebroad (Dec 10, 2013)

This is where I got my information:
http://energy.gov/energysaver/articles/thermostats


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## semipro (Dec 10, 2013)

firebroad said:


> This is where I got my information:
> http://energy.gov/energysaver/articles/thermostats


Great site. Thanks for posting.  
There's a very direct and simple explanation of why setting back works there. 
It goes into how even heat pump and boiler based system users can benefit from setting back with the right thermostats.


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## 1750 (Dec 10, 2013)

begreen said:


> It depends on the heating system and it's recovery time. High output systems like oil and gas furnaces can see a significant savings with a setback thermostat as long as the set back isn't too radical. 5 degrees is usually plenty.



Can you help me understand why this same thing wouldn't be true if you turn back the thermostat more substantially (e.g., 10 or more degrees)?   It seems like the same variables would work in your favor, but I admittedly don't know much about this.



firebroad said:


> This is where I got my information:
> http://energy.gov/energysaver/articles/thermostats


Thanks for posting this.   

"...By turning your thermostat back 10° to 15° for 8 hours, you can save 5% to 15% a year on your heating bill -- a savings of as much as 1% for each degree if the setback period is eight hours long."


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## semipro (Dec 10, 2013)

1750 said:


> begreen said: ↑ It depends on the heating system and it's recovery time. High output systems like oil and gas furnaces can see a significant savings with a setback thermostat as long as the set back isn't too radical. 5 degrees is usually plenty.
> 
> 1750 said: Can you help me understand why this same thing wouldn't be true if you turn back the thermostat more substantially (e.g., 10 or more degrees)? It seems like the same variables would work in your favor, but I admittedly don't know much about this.


I suspect that the limit to how far you can set back is dependent upon how fast your HVAC can recover.  If you were to set back too far (and/or too long) your system might not be capable of bringing temps up to desired levels fast enough.


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## dmmoss51 (Dec 10, 2013)

Boiler's might be different because you have the water to keep hot anyway.  I think there can be a decent amount of savings with forced air as you are reducing the amount of times it cycles during the day when no one is home, and also subracts from the time that that fan runs on the electric side too.  The problem is if you set it down too many degrees it runs for one long cycle when it goes back up that is longer than the missed cycles combined.

Also its a great combonation with wood heating as our furnace hardly ever runs anyway, but won't call for heat if it cools off a little bit before I get home and rekindle the fire.  Then My goal is to get the stove heating the house before the thermostat calls for heat.


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## btuser (Dec 10, 2013)

Adios Pantalones said:


> "
> 
> Temp swings may be bad for some stuff in your house, and may overwork a boiler (I guess), but the thermodynamics of this are pretty clear.



Yep.   A btu unburned is a btu earned.

(hey, that would make a good t-shirt)


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## fbelec (Dec 10, 2013)

don't forget when the sun is out giving solar heating it might not actually heat your house but the outside wall thinks it a little warmer and doesn't lose it's heat as fast. then the sun goes in the temp of the wall drops and at 5 or 6 o'clock when the heat comes on it has to over come the cool air in the house the cool wall and the temps outside. then when the air is heated the heater is not done. you'll notice it come back on sooner than normal because it takes more time to heat the walls. the hardest thermostat to control is the one that puts the wood in the stove. sometimes it's just one log to many or one to short and the back has to pay for that one


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## firebroad (Dec 11, 2013)

dmmoss51 said:


> Boiler's might be different because you have the water to keep hot anyway.  I think there can be a decent amount of savings with forced air as you are reducing the amount of times it cycles during the day when no one is home, and also subracts from the time that that fan runs on the electric side too.  The problem is if you set it down too many degrees it runs for one long cycle when it goes back up that is longer than the missed cycles combined.



Actually, I find that my HP fan runs so much while maintaining heat that that isn't really true.


_*"Also its a great combonation with wood heating as our furnace hardly ever runs anyway, but won't call for heat if it cools off a little bit before I get home and rekindle the fire.  Then My goal is to get the stove heating the house before the thermostat calls for heat"*_

I do the same thing!  Soon as I get home I race for the stove to get it going before the system kicks in. (Sometimes I cheat and turn it down.)


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