Programmable Thermostats and Energy Savings

[inquisitive]

Just had a programmable thermostat installed today. Does anyone know if it is okay to have large variability in the temperature? I set it for 55 degrees Fahrenheit during the day when no one is home and then 64 degrees starting in the evening.

During the night I am having it go down a few degrees but seeing as there are only 2 bedrooms that need heating during the night would it be more cost effective to have the temperature go down considerably at night and use space heaters for the 2 rooms instead of heating up the whole house? I have a gas heater.

 

[NW-Bound]

How do you heat?

In my case with a central heat pump, if the house temperature is too low compared to the thermostat setting, the heat packs (resistance heaters) would kick on. Heat packs are not as efficient as the heat pump of course, so that costs more. Additionally, my electric bill is on "demand rate", which in the winter costs more for the period from 5PM to 9PM.

YMMV. A lot!

 

[W2R]

The answers to be posted on this thread should be very interesting to me. I suspect that it may not make much difference, but I do not know that.

I have a programmable thermostat, and have been saving money in a way that may be repugnant to most, but that works for me. Instead of programming it for comfortable temperatures, I have left the default temperatures in place, which use less energy during the daytime when most people are at work. In the late afternoon temperatures are about 10 degrees hotter than I might like with the A/C on (I think about 85) and 10 degrees colder than my ideal with the heater on (I think about 65 at that time of day). When I feel uncomfortable enough to do so, I use the manual override but that only lasts for a few hours.

Sounds silly but waiting until I am uncomfortable enough to actually DO something about it, seems to lower my energy usage. Another good result for me is that I have developed a wider range of temperatures that are comfortable to me, than previously. After years of following this method, often I don't bother to use the manual override at all any more.

 

[inquisitive]

I have a gas heater with forced hot water.

I've set the thermostat for 64 for when I am home. I have to dress warm but find that it is not too uncomfortable.

Does anyone know if I will lose more money in heating costs from heating the place from 55 to 64 when I arrive, rather than maintaining it at a higher temperature? I do have a newer energy efficient heater.

 

[Telly]

O/P, since you have gas heat, I don't see anything wrong with setting the house temp down to 55 during the day.

I have no idea what your climate is like, but if it's a cold one, if the temp at the thermostat is 55 degrees, will a water pipe in the most vulnerable place be kept ABOVE freezing even on the coldest run of days in winter? Like a water pipe in an outside wall, or a water pipe under a kitchen sink against a cold wall, etc.

As to your question of running space heaters to allow the house temp to be lowered further than present value at night, I wouldn't do it. You might not save anything, the cost of the electricity to run the space heaters may be more than to run the furnace.
But more importantly, I think in general, space heaters are a BAD idea. For a specific use, by a observant person, for a short period of time, I think it would be OK, like warming a garage while working out there. But not every night in a bedroom, with people asleep.

Candles and space heaters are some of the most common causes of major house fires, often resulting in deaths. It's a step I would not take. Too risky.

 

[Telly]

I have a gas heater with forced hot water.

I've set the thermostat for 64 for when I am home. I have to dress warm but find that it is not too uncomfortable.

Does anyone know if I will lose more money in heating costs from heating the place from 55 to 64 when I arrive, rather than maintaining it at a higher temperature? I do have a newer energy efficient heater.

No, you will save money. The heat loss from the building decreases as the temperature differential between inside and outside decreases (the falling inside temperature). The heat will not run for a long time after the temp setting is lowered from 64 to 55. And it will run less at 55 than it does at 64 degrees setpoint. Yes, it will run what seems like a long time to bring the temp back up to 64, and it will cycle more often right after it gets back to 64 (needs to warm up objects and walls, etc., the inside thermal mass of a house). But the not-running much at 55 will more than make up for that.

 

[samclem]

I'm with Telly on the space heaters in bedrooms--not a good idea. Consider another blanket or even an electric blanket (Some folks just use the elcric blanket to warm up the bed before they get in)

Regarding the efficiency of steady temps vs fluctuating: It is more efficient to let them fluctuate (colder when no one is home, then heating up before everyone gets home). In rough terms, your house loses heat in a fairly direct proportion to the difference between the temps inside and the temps outside. If it is 70 deg inside and 30 degrees outside (temp difference of 40 deg) you'll lose heat twice as fast as if inside temp was 50 degrees at the same outside temperature (temp difference 20 degrees). So, your furnace doesn't have to burn much gas to replace the lost heat.

Now, you have a modern, high-efficiency furnace, probably with a multi-stage burner. At least with forced air heat, in most installations when the thermostat tells the furnace that the temp inside the house is way cooler than the set temperature, or if the temperature stays below the set point even after the furnace has been running for awhile, then the furnace goes to a higher setting (burning more gas and running the fan at higher speed). It will go to this high setting when the timer on the thermostat calls for a the big temperature rise before everyone gets home. My guess is that it burns gas slightly less efficiently at these higher settings. Still this impact will be minuscule compared to the gas you saved with the lower thermostat setting in the preceding hours

 

[NW-Bound]

Both of my houses are all electric, but I completely agree with others that you would save money by letting the house get colder while you are not there, since you are using gas. Electric heating in my case brings more complications to the issue along with the demand rate. When there are non-linearities in a system, optimization is a very tricky process.

Regarding an electric heater for a small room vs. cheaper gas for an entire house, I cannot comment because it involves a trade-off. How much is your electric rate vs. the cost of gas? How big is the bedroom vs the entire house?

Can't you turn down the radiators in the rest of the house, while running the bedrooms at a higher water flow? I never have this kind of system, so do not know what controls are available.

In our case, we set the temperature in our boonies home at a permanent 45 deg F year round, as cooling is almost never needed at 7000ft. A space heater keeps our bedroom at 60 deg F at night and an electric blanket keeps us comfortable even when the temperature outside gets as low as 0 deg F. By the way, we have a benefit of passive solar heating during the day, which nearly always works given the usual clear AZ sky even in the winter. My neighbor with a much smaller house has been paying $500/month for propane, in addition to more than $100 for electric. Our electric bill in the boonies home was never more than $100/month. The cooling bill for the low-desert home is an entirely different and scary thing.

 

[Midpack]

Just had a programmable thermostat installed today. Does anyone know if it is okay to have large variability in the temperature? I set it for 55 degrees Fahrenheit during the day when no one is home and then 64 degrees starting in the evening.

You will save money for sure. We keep ours at 66F when we're home/awake and 61F the rest of the time. Our house wouldn't drop all the way to 55F at night even if we set it that low (I've looked in the AM before the higher setting takes effect), but it doesn't hurt anything. You will enjoy the savings.

 

[inquisitive]

I have no idea what your climate is like, but if it's a cold one, if the temp at the thermostat is 55 degrees, will a water pipe in the most vulnerable place be kept ABOVE freezing even on the coldest run of days in winter? Like a water pipe in an outside wall, or a water pipe under a kitchen sink against a cold wall, etc.

Thanks for all the great responses everyone! My place is not that big so I don't think it makes sense to get space heaters for the 2 bedrooms, plus all the risks that people have brought up, and I am having the temperature go down to 60 at night anyway. I have a gas heater with forced hot water.

About pipes freezing, I did some searching and 32 degrees is the temp at which they will freeze. If I let the house temp fall to 55, I can't imagine any pipe getting to 32 degrees and according to someone's answer on a Yahoo Answers page the temp should be kept above 50 to prevent freezing. So I think it should be okay.

 

[hguyw]

In the spring and fall, I override the programmable thermostat a lot to save even more. Instead of letting it come on automatically so the house is warm when I get home, I'll put it on 'hold' and then turn it up ('run') when I get home. Probably gets me an extra 45 minutes of no furnace running every day.

I've always wondered about the idea that programmable thermostats save money...I guess alot of people keep theirs at 72 degrees, 24/7? I never did that (manually turning it down at night and before leaving the house) so I'm not sure the progammable saved me that much. But the old one (50+ years old) was shot so had to be replaced with something.

BTW, I've read that if you're leaving the house for less than 3 hours, it's more economical to leave the heat turned up. More than 3 hours, turn it down.

 

[LOL!]

I think the cost will depend on the average temperature you have set versus the average outside temperature. The work done (and energy used) will be the same. So going 55 when gone and 64 in the evening might be the same as 64 all day long if the outside reaches 60 because it will take a while to cool the inside to 55 for the heat to come on and the inside is often warmer than the outside.

We use down comforters at night.

 

[Gearhead Jim]

How do you heat?

In my case with a central heat pump, if the house temperature is too low compared to the thermostat setting, the heat packs (resistance heaters) would kick on. Heat packs are not as efficient as the heat pump of course, so that costs more.
...
YMMV. A lot!

Same situation for us, in northern Illinois.

The electric resistance heaters use several times as much electricity per unit of heat as the actual heat pump, especially if you kick in the reistance when it's not very cold outside. (If your aux heat is gas instead of resistance electric, a different story).

However, if it gets below 0'F, then the heat pump isn't very efficient and bringing in the resistance heat is not so bad, comparatively.

We use a night setback temp of 67', warm up to 69' at 7am and 71' at 8am. Using two stages like that reduces the resistance heat use.
Some HP gurus tell use to not use any setback at all during the coldest months.

In our case, we built our 3,800 sf house 28 years ago with energy conservation as part of the plan. Everything is electric- heat, cooking, water heater, our well pump, septic pump, etc. So our only utility bill is electricity; it's below $300 during winter and more like $125 in summer, less in Spring and Fall. That's about 1/2 to 1/3 of what most of our neighbors, even with gas heat, are paying. Insulation + windows properly placed and sized, did pay off.

 

[NW-Bound]

We use a night setback temp of 67', warm up to 69' at 7am and 71' at 8am. Using two stages like that reduces the resistance heat use.

In our case, we built our 3,800 sf house 28 years ago with energy conservation as part of the plan. Everything is electric- heat, cooking, water heater, our well pump, septic pump, etc. So our only utility bill is electricity; it's below $300 during winter and more like $125 in summer, less in Spring and Fall. That's about 1/2 to 1/3 of what most of our neighbors, even with gas heat, are paying. Insulation + windows properly placed and sized, did pay off.

Very impressive, considering your house is larger and you keep it warmer. My hat off to you.

 

[Gearhead Jim]

Very impressive, considering your house is larger and you keep it warmer. My hat off to you.

I'd like to say it was genius, but dumb luck played a large part.

 

[bosco]

With electricity at $.22/kwh where I am currently living, electric heat is simply not an option.

My "programmable therostat" consists of setting the monitor stove to 55 degrees, and throwing another log in the wood stove if I get cold.

The monitor almost never kicks on except a bit in the middle of the night if the stove goes out.

It's effective, cheap, and in the case of the wood, carbon neutral. I'm living in a small cabin this winter (starting construction of a 1700sf house next spring), but will use basically the same method for it.

 

[ziggy29]

Ditto the comment about the heat pump. We have one with electric re$i$tance auxiliary heat, and if you set it to 55ºF while you're gone and set it to 70º at 5 PM, there's a good chance the heat strips will kick in and wipe out much of the savings.

We set ours to a constant 68º for heating and a constant 78º for cooling; since I work at home there's no need to create a special "daytime M-F" setting. It's quite rare for the electric resistance heat to kick in here; usually it has to get down into the low 20s for that to happen -- and we only have that happen a handful of times each year in the overnight hours.