Aux Heat Kills
Have you ever wondered whether Mother Nature is trying to teach you a lesson?
Neither have I, until I got my electric bill this month.
If you’ve been following this blog awhile, you’ll know that I always track my electricity consumption versus the average monthly temperature. That helps me sort out the effects of weather on my bill, and see how much I’ve saved by insulating and installing a programmable thermostat.
You’ll also remember that I made a BIG mistake by letting the auxiliary heat on my heat pump turn on a lot over the winter. I’ve tried to correct that problem with a new thermostat that allows me to disconnect the “electric furnace” whenever I want to. It’s already saved me some cold hard cash in January, and I was hoping to see the same savings in February.
But it turns out I saved even more… over $50 in a single month!
To what do I owe this honor and surprise? Was it my perfect diligence at turning out the lights? The five-minute, cold showers I took every morning to save energy? The fact that I ran in circles around the house trailing wet towels behind me rather than turn on the dryer?
Nope. Because I didn’t do any of those things. In fact, I don’t think I did anything differently.
Well, perhaps it was warmer out, on average, and that saved on my heating costs.
Nope. Looks like January and February had the same average temperature. So why did I save 50% more?
It’s a classic case of the Flaw of Averages. Take a look:
This chart shows the daily temperature range in Chapel Hill. The red line runs along 30 degrees – below this temp, my heat pump can’t keep the house warm, and the strip heaters turn on, consuming 5 times more energy.
It’s pretty easy to see that January had a LOT more days where the temperature was dipping into the 20′s. There were a couple of cold weeks, followed by a couple of warm weeks, so the average temperature for January is pretty close to the average temp in February, it’s just that January had a lot more variation.
So now I know – given two “equally cold” months, running the auxiliary heat can cost me 20-30% more than just using the heat pump. Lesson learned – thanks Mother Nature! Now seriously, you’d better warm things up, or I’m going to get really mad.
One final point before someone asks – yes, heating degree days can account for this type of change better than the average temperature could, but it introduces some other errors. We’ll save that discussion for another post!
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