What Temp to Keep House while Away?

[TheDuckRocks]

Thank you all for the info about heating a house. I have learned a lot.
Just a little more for those of you who have been following these posts. Our house is all electric. It also runs with a heat pump system. I just verified both of these statements from documents provided from the home builder.
Not being an engineer nor someone who really has much understanding of the concept of heating a house, other than to turn the thermostat to the temperature I want, I am very serious that my understanding has increased.
As a retired accountant who still loves spreadsheets, I'm looking at the whole heating issue on a dollars and cents basis. The info about not going over changing the temp only 2 degrees at a time and keeping general change to a minimal amount will help me with lower electric bills this winter.

[1DisneyNut]

:Sigh:

Since multiple people have mis-stated my reply, I will reiterate that my statement involves the amount of ENERGY used, not COST. Yes of course you can come up with odd scenarios if you re-warm the house using inefficient heat sources or highly priced energy as compared to the normal baseline methods.

The science is not exactly complicated. The longer you maintain a large temperature differential the greater amount of ENERGY will be needed to maintain that differential. I could go on but I don't see much of a point if people are going to mis-interpret what I said.

OP: Most recommendations will tell you that 50-55 should be fine unless you have pipes in areas that get especially cold like a partially warmed entry-way or something. Set it at 55 and have a nice trip.

I am also an engineer and will give my two cents worth. As others have already pointed out, there is a flaw in your original response. You are of course completely correct in your assertion it should take less energy to heat a house back up rather than maintain a consistent temperature. However, the problem is the type and efficiency of the heat producing equipment.

If the home had a heating unit that had only one way of producing the heat such as a gas furnace, oil heat, etc. then it would always 100% of the time use less energy and therefore cost less to heat the house back up rather than maintain the consistent temperature as you stated. This is because the efficiency of the unit is always consistent. On the other hand, as has been pointed out, heat pumps kick into "emergency heat" mode when they fall behind more than usually 3 to 5 degrees which uses extremely less efficient electric heat strips. The heat strips are basically a big version of one of those cheap plug in electric heaters where the wires glow red that you can buy at walmart.......extremely inefficient. This causes the heat pump to typically use 25 to 40% more energy while trying to bring the house back up to temperature whereas it would have been extremely efficient (more efficient than aforementioned gas and oil furnaces).

Depending on various factors including the outside temperature, SEER rating (efficiency) of the heat pump, R-value insulation of the home, thermal efficiency of the windows, etc. it could take 2 weeks or even more than a month of the heat pump being set at 50 for it to overcome the energy loss due to inefficiency of the heat strips while trying to recover.

Long story short, if it is going to be below 45 outside and you are going to be gone less than 2 weeks, only drop the temperature setting about 3 degrees and you will save a slight amount of energy and cost. It will also help save if you wait until night after the electricity rate has dropped to night rate before you raise the temperature back up assuming your electric company uses variable demand rates but that is also not a given. If the temperature is drastically colder at night, your unit may have to use the heat strips to recover and it would have been cheaper to raise the temperature back up during the day on the higher demand rates. When it comes to heat pumps, there is a lot more at play than simple thermodynamics.

[Tekneek]

When the air conditioning is on, I set it at 85. When the heat is on, I set it at 55.

[MIKESMOM]

I live in Maine,so our temps are similar to yours. I heat my home using oil, we have forced hot air. When we are away we turn our electric hot water heater off, and turn our heat down to 50.I open the cabinet doors under the sink just as a precaution. We have never had any problems even when the temps have gone down in the negative range while we were away.

[HollyB]

We are currently in the deep freeze here in Illinois. All the media outlets are running stories on how to prevent pipes from freezing. General consensus is to set your heat no lower than 55 degrees, leave sink cabinet doors open, and allow your faucets to drip a little--about once every 10 seconds. If there is low risk of power outage (i.e., you aren't expecting major storms while you are away), you can likely skip the dripping.