How cold can you reasonably program your t-stat to drop to during the day?

[Virge_]

Assuming the outside temperature drops below 0 degrees and you have a programmable T-stat with an away schedule, how cold is it reasonably safe to let the inside of the house dip to before you run into potential issues with pipes/etc?

 

[lxskllr]

If you're talking about a work day, I only adjust by 3° or 4°. For extended away time, I'd set it to 40°.

Edit:
You'd probably be ok at 33°. That's above freezing, and you really only need to protect against a hard freeze. A bit of ice in the pipes won't hurt.

Heavily insulated, it can takes days to get down from a 60 degree sunny day. Solar panels supplement the heat.

 

[nageov3t]

assuming you have half-decent insulation and won't be gone longer than a typical work-day + commute, I can't imagine it's something one needs to worry about outside of the arctic.

I have my thermostat programmed to drop down to 50F when I'm at work and don't think much about it (with 67F kicking in about half an hour before I get home)

 

[EagleKeeper]

We have our house in the hills to allow 40. The difference between that and 34 is mot much difference and it is great psychologicaly. Movement in tbe entry way, triggers the heater override.

Realize the place is empty 6-8 months a year when on tbe road.

 

[Virge_]

Supplementary information to answer two PM's: I have an extremely good HVAC config (20 seer dual-compressor AC, 97.5 AFUE three-stage variable speed furnace/air handler) paired with a fully enclosed electronic 5" air filter that runs at 50% fan speed 24/7 for allergies. The house has superb insulation but is a larger tri-level (3600 sq/ft not including 975 sq/ft basement). I use a XL950 t-stat which allows me to set multiple temp alerts, so I have the stat e-mail/text me at 60, 55, and 50 degrees.. and I set the house to not engage until 50 degrees during the hours of 9-AM till the home point (currently set to 4:45PM). The XL950 learns how hard and fast it needs to work to kick in and get the temp to 70 degrees by 4:45 based on the difference between outside and inside temperature, so if it takes 45 minutes to get to 70 it turns on at 4, 60 minutes 3:45.. etc.

Last few days were -10 degrees, and the house hit 60 by 1PM, 55 by around 3. I'm primarily just making sure there isn't some common set point above the obvious 32 degree freezing point that I should be aware of for appliances or general building construction that would suffer dramatically past a certain point. Overall by doing this I've saved roughly 40% on my gas usage for the furnace as opposed to keeping the system running all day while I work.

Thanks for the replies so far!

 

[EagleKeeper]

The main thing to realize is you will stress the system to bring it up to a comfot level once you get home or have it programmed to kick back in.

 

[Virge_]

The main thing to realize is you will stress the system to bring it up to a comfot level once you get home or have it programmed to kick back in.

Given the information above, could you possibly supplement and be more as specific as to how/why? It seems to me that doing a hard burn for 45 minutes would be significantly less stressful overall vs. running on low all day.

 

[sixone]

Our local electric co says not to vary the temp by more than 8 degrees, either at night or when no one's home during the day.

At more than 8 degrees, the cost of reheating the place outweighs the savings from having it turned down.

 

[Virge_]

Our local electric co says not to vary the temp by more than 8 degrees, either at night or when no one's home during the day.

At more than 8 degrees, the cost of reheating the place outweighs the savings from having it turned down.

I'd be willing to bet their calculations were done based on some study with the majority of homes with shitty insulation using builders grade 10-13 seer equipment, in addition to being geographically-specific. Not really applicable here.

 

[Howard]

Our local electric co says not to vary the temp by more than 8 degrees, either at night or when no one's home during the day.

At more than 8 degrees, the cost of reheating the place outweighs the savings from having it turned down.

I can't really see that happening. I'd like to see that math.

 

[skyking]

If you have any house plants, keep it at 60 minimum.

 

[EagleKeeper]

Given the information above, could you possibly supplement and be more as specific as to how/why? It seems to me that doing a hard burn for 45 minutes would be significantly less stressful overall vs. running on low all day.

I have to take the furnace experts word on such.

Possibly that the 45 minute hard burn is heating up the air only; not the heat sinks (furniture) in the house.

 

[who?]

Our local electric co says not to vary the temp by more than 8 degrees, either at night or when no one's home during the day.

At more than 8 degrees, the cost of reheating the place outweighs the savings from having it turned down.

The electric company may be worried about the total continuos demand if everybodys heat is running full blast for that long simultaniously. Why am I not seeing spell check here?

 

[sixone]

The electric company may be worried about the total continuos demand if everybodys heat is running full blast for that long simultaniously. Why am I not seeing spell check here?

Not likely. Gas heat is as common here as electric.

I don't know what they based it on. Just relaying info - do with it what you will.

 

[Triumph]

Our local electric co says not to vary the temp by more than 8 degrees, either at night or when no one's home during the day.

At more than 8 degrees, the cost of reheating the place outweighs the savings from having it turned down.

It's such a fickle calculation that you're not really going to be able to say exactly 8 degrees for everyone. Maybe I only work a half day, then in that case I probably was better off leaving it at 68 while I was gone for 4 hours. Maybe my house is on a hillside that gets a lot of wind blast, rapidly robbing heat. Maybe my insulation and furnace is super efficient. Maybe it's -20 outside. Or if I'm gone for 2 weeks, no way is the cost of keeping it at 60 degrees less than the cost of reheating from say, 50.

But the OP wants to know, presumably, how cold he can go before things start breaking. Well, house plants will die if you have them. And your house doesn't heat and cool evenly. Setting your thermostat at 35 degrees might sound ok, but is it 35 degrees everywhere there is a pipe in your house? What about the slab itself, it may have your water line running through it. When I go away, I set it at 60 - I would feel safe going lower but I killed one house plant that way so I'm not doing that again.

 

[Jeff7]

I can't really see that happening. I'd like to see that math.

Same here.


The larger the temperature differential between inside and out, the more heat transfer you'll get. If you're expending energy to keep your house's temperature elevated when it's cold outside, you'll lose more heat for the entire time it's being maintained at that warm temperature.
Turn off the heat, and the rate of heat loss will decline as the house's internal temperature approaches that of the outside air, and that's all time that you're not spending money to push energy back into the house.
Ohm's law still works here.
V=IR
I=V/R
Heat transfer = difference in thermal potential / thermal resistance