An Energy Update

>> Sunday, January 11, 2009

I've been working on making my home more energy efficient, and feeling inspired by my friend Maren, I decided one night to bump our heat down to 60 to see if we survived. I put a space heater in the boys' room since Third Son is not yet old enough to sleep with a blanket, and my husband and I cuddled up under a stack of blankets. Actually, the blankets were for me because my husband exudes body heat and rarely ever feels cold. If you've read the Twilight series, you'll understand what I mean when I say that I think he's part werewolf.

Anyway, when we woke up in the morning we discovered two things about our apartment:

1) We have a heat pump.

This is an important thing to know because a heat pump does not work the same way as a furnace, so the blanket statement "Turn down your heat at night and when you're away from your home" does not completely apply to those of us with heat pumps.

We had a heat pump in our last home also, so as it was explained to me by the guy who inspected our home before we bought it...Unlike a furnace, which heats up the air, a heat pump draws heat from the outside air and pumps it indoors. When the outside air drops too low, the heat pump kicks on a backup heating source, which is made up of a panel of electric coils.

Heat pumps are great for moderate-to-warm climates because they are very energy efficient. According to the U.S. Department of Energy, "an air-source heat pump can deliver one-and-a-half to three times more heat energy to a home than the electrical energy it consumes." If you live in a cold climate, though, a heat pump is not a good idea because the heat pump will have to work harder to heat your home and will end up using that backup heat source a lot, which is more expensive and less efficient than the heat pump mode.

We even ran into problems with the heat pump in Maryland, which is not a very cold place but does get snow a few times a year. Without fail, our heat pump died after the first snowfall every winter we lived in that house. The thermostat said it was running on backup heat, but the backup heat could never get our house back up to a comfortable temperature and we would have to get it repaired. I don't know if that's typical of heat pumps, I'm just saying that's what happened to us.

The point of all this jibberish is to say that if you have a heat pump and you follow the typical advice of lowering your heat at night, you end up losing on efficiency because when you raise your heat, the heat pump will kick on its backup heat, which as I said, is more expensive and less efficient to use.

So that leads to the second discovery about my apartment:

2) It faces south.

My husband and I have been talking about someday building a passive solar house for a couple of years now, so my brain is full of research on this subject. I'm not going to go into too much detail here, but basically, it works like this: you design your house so that the south side contains most of the windows to allow the winter sunlight to enter the home. You also need a thermal mass that soaks up the heat during the day and then releases it at night, keeping your house at a nice cozy temperature of 65 to 70 degrees. Generally, this means that your house is built on a concrete slab. You can also create a thermal mass by building an interior wall of brick or stone.

We are on the second floor of an apartment building, so we don't have any thermal mass per se. But our apartment does face south, and that whole side of the apartment has huge picture windows.

So that morning after I'd dropped our heat down to 60, I woke up and went to the thermostat to raise the temperature back to a more comfortable 68. (This, by the way, was a huge sacrifice to me as I am a cold-natured person and prefer a house around 75.) As soon as I bumped up the temperature, I noticed the light come on the thermostat indicating that the backup heat source was being used. That's when it dawned on me that we had a heat pump.

I grudgingly dropped the heat back down to 60 and went to find a sweater. A couple hours later, I noticed as I was walking past the thermostat that it said that the temperature was 65, even though I had it set at 60. A couple hours after that, the house was up to 70 degrees.

Since then, I've kept the thermostat set at 60 degrees all the time. During the day, the house warms up to 70 by noon just with the warmth of the sun. At night, the kids have a space heater, and I have my werewolf to keep me warm.


Maren Hansen January 12, 2009 at 9:36 AM  

Now I'm feeling slightly guilty... ;) Actually, the good news for you is that you really do get used to the lower temperatures. I'm not so sure your blood actually thickens, but I do know that we are all pretty used to the low temps and even find 65 warm at times! You're amazing, Erin!!

Joyce January 12, 2009 at 11:52 AM  

Interesting post! I didn't know that heat pun=mps were less efficient up here, but after your explaination, I can see why.

I think thermostat settings can depend a lot on how drafty your home is. It's not so bad in the low 60s, if you have nice tight windows, but if you don't it can be fairly miserable.

Erin aka Conscious Shopper January 12, 2009 at 8:30 PM  

Maren - You shouldn't feel guilty. You were a great inspiration!

Joyce - You're right about the thermostat settings depending on how drafty your house is. We stayed at my sister's house in Philly over Christmas, and she keeps her house at 66 there. So in theory it should have felt warmer than my house, but because her house is very old and drafty (and maybe not insulated properly), I was constantly cold.

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