Is the EPA and Consumer Reports propogating myths about conserving heat?

[John Ackerly]

The EPA and Consumer Reports keep advocating lowering your thermostat 5 to10 degrees at night or when you are not at home. What is the science behind that? Isn't lowering it 15 - 20 degrees or completely shutting off your heat at night or when you are not at home much more energy efficient? I suppose they are just urging folks to do what they think is practical, but they do a great disservice to all those ready and willing to do more than just 5 or 10 degrees. I keep meeting people who think its more energy efficient to keep your house at a consistent temperature, rather than having to cool it down or heat it back up again. This has been disproved many times. But EPA and Consumer Reports may play into that myth by suggesting its more energy efficient to only adjust your thermostat by 5 or 10 degrees. Am I missing something?

 

[vvvv]

heatloss is determined by the temp diff between indoor & outdoor. lowering indoor temp saves energy & aint rocket science.

 

[oldspark]

Yea maybe they do not want to hang meat in their house( :lol: ) I think it is just a suggestion as to what they think people will do, not to many people willing to set the thermostat at 50 degrees at night.

 

[vvvv]

Yea maybe they do not want to hang meat in their house( :lol: ) I think it is just a suggestion as to what they think people will do, not to many people willing to set the thermostat at 50 degrees at night.

10*f drop in temp is practical temp drop for interior, if i remember

 

[btuser]

I've been up and down this a few times. The colder your house the less it costs to heat. Its a linear graph too, meaning a greater differential isn't more efficient. So if 5 degrees saves you 5% and 6 degrees saves you 6% then 10 degrees will only save you 10% and 30% and so on.

Here's where there's a problem with "too much" recovery: It takes a lot to push your house back up to 68 degrees, and we Americans are an impatient breed, so the tendency (in fact the norm) is to OVERSIZE a system. Most homes in the US would have no problem recovering from 10 degrees in an hour, and that's actually pretty bad unless you have a modern system with a modulating burner, indoor sensors, and expensive controls. Most boilers are 2x the real need for a system, and when you factor system efficiency instead of the bogus AFUE standards you realize its closer to 60% than 80%. I spent about $200 on setback thermostats, then got a boiler with outdoor reset so now recovery takes too long, so now all the nice new thermostats are set to a standard temp.

I keep the house @ 60, the bedrooms @ 62, and if someone wants it warmer its time for a fire. There's the wood, right next to the stove.

 

[begreen]

The EPA and Consumer Reports keep advocating lowering your thermostat 5 to10 degrees at night or when you are not at home. What is the science behind that? Isn't lowering it 15 - 20 degrees or completely shutting off your heat at night or when you are not at home much more energy efficient? I suppose they are just urging folks to do what they think is practical, but they do a great disservice to all those ready and willing to do more than just 5 or 10 degrees. I keep meeting people who think its more energy efficient to keep your house at a consistent temperature, rather than having to cool it down or heat it back up again. This has been disproved many times. But EPA and Consumer Reports may play into that myth by suggesting its more energy efficient to only adjust your thermostat by 5 or 10 degrees. Am I missing something?

Actually there is some testing behind this. If you set back the temps too far the system can spend half a day trying to get the house back up to temperature. The reason being you are not just lowering the temperature of the house, but of all the mass of it's contents, walls, etc. too. At a certain point it takes more energy to raise the temperature back to the comfort level than is saved by a large nightime setback.

Testing has shown the average ideal is about 5-10 degrees depending on the house and the heating system. Some heating systems are more closely tuned with the house btu requirements than others. Heatpump and some radiant systems take a bit longer for example. So for example, with a heat pump system it's usually more efficient to just do a 5 degree setback.

 

[semipro]

I think the work that EPA bases these numbers on research done by Oak Ridge National Labs. This document may be the one. http://tinyurl.com/ydx6s4t

 

[semipro]

I've been up and down this a few times. The colder your house the less it costs to heat. Its a linear graph too, meaning a greater differential isn't more efficient. So if 5 degrees saves you 5% and 6 degrees saves you 6% then 10 degrees will only save you 10% and 30% and so on.

Here's where there's a problem with "too much" recovery: It takes a lot to push your house back up to 68 degrees, and we Americans are an impatient breed, so the tendency (in fact the norm) is to OVERSIZE a system. Most homes in the US would have no problem recovering from 10 degrees in an hour, and that's actually pretty bad unless you have a modern system with a modulating burner, indoor sensors, and expensive controls. Most boilers are 2x the real need for a system, and when you factor system efficiency instead of the bogus AFUE standards you realize its closer to 60% than 80%. I spent about $200 on setback thermostats, then got a boiler with outdoor reset so now recovery takes too long, so now all the nice new thermostats are set to a standard temp.

I keep the house @ 60, the bedrooms @ 62, and if someone wants it warmer its time for a fire. There's the wood, right next to the stove.

I don't think it is a linear relationship. Heat flows faster when the temp difference is greater as Blimps says. Even though the temp difference of 10 is the same you'd use much more energy going from 70 to 80 than you would going from 60 to 70.

 

[benjamin]

Actually there is some testing behind this. If you set back the temps too far the system can spend half a day trying to get the house back up to temperature. The reason being you are not just lowering the temperature of the house, but of all the mass of it's contents, walls, etc. too. At a certain point it takes more energy to raise the temperature back to the comfort level than is saved by a large nightime setback.

Testing has shown the average ideal is about 5-10 degrees depending on the house and the heating system....

So for example, with a heat pump system it's usually more efficient to just do a 5 degree setback.

I think this is mostly an issue of making a broad recomendation that people might be willing to try and stick with.

The issue with heat pumps is that many of them go into "second stage" which is electrical resistance heat if they get behind. Obviously you're not saving energy if you're replacing pumped heat with resistance heat. Aside from heat pumps, I disagree with Begreen. The more you're willing to let the temp drop, the more benefit you derive from mass and Tstat setback.

If you really want to save energy then the Tstat setback is irrelevant because a house can easily be efficient enough to hold it's temperature better than even 5 degrees overnight.

 

[begreen]

I wish all houses were tight and efficient, but this is far from the reality of American housing. I haven't tried it, but I would guess that our old farmhouse would lose at least 15-20 degrees on a cold, windy, winter night without any heat. That would take most of the day to warm the house back up again using our big woodstove, especially if the conditions outside didn't change and temps were in the teens.

But, you are correct, in some cases you will benefit from a larger setback. If this is an efficient home envelope with a forced air system, then a savings can be had with the larger setback. As noted, it depends somewhat on the heating system. Systems with slow recovery don't benefit from large temperature drops. Examples would be heat pumps, electric resistance heat (very common), radiant floors and some steam heating systems.

http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12720

 

[benjamin]

If this is an efficient home envelope with a forced air system, then a savings can be had with the larger setback. As noted, it depends somewhat on the heating system. Systems with slow recovery don't benefit from large temperature drops. Examples would be heat pumps, electric resistance heat (very common), radiant floors and some steam heating systems.

http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12720

Now I disagree with .gov and BeGreen. In my mind a drafty house with resistance heat will benefit most from setting back the thermostat.

Again, if there is not an electrical resistance heat second stage involved, then a heat pump will have the same savings as any other heat source. If the heat pump is not capable of catching up then it will be an issue of slow recovery, meaning more discomfort if the thermostat isn't set with the delay accounted for, but could only use more energy if they overshoot the setting, or if the efficiency of the system drops from the higher output temp (steam or hot water).

The only house that won't save energy by turning down the thermostat is the one that doesn't lose heat.

 

[dvand]

One thing also to consider is I believe you can get some risk of condensation if you drop temperature too far.

 

[freeburn]

One thing I notice is that if the walls (plaster) in my house get too cold, the whole house cools down. Makes sense since plaster might just as well be concrete. Keep the walls warm enough and the house stays warm overnight. Follows the same line of thinking as the radiant floor heat, but in the walls.

 

[Seasoned Oak]

Keep my house at 76 All winter, I have setback thermostats but they dont work well in very cold months as my system is NOT oversized.
Found it works much better to just set it and forget it. Also domestic hot water overrides the radiation so if theres several people showering one after another the house heat may be off for awhile so i have some ways to go before it actually gets cold in the house.