Oddly, gas was a little tougher to get a handle on – there is a lot more variability month-to month, as well as year-to-year depending on the weather. Our therms used per billing period has ranged from around 10 to almost 200 in the last 3 years. I’ve also done a lot of work that should help things (note, some amazon affiliate links follow):
- Sealed the attic and added insulation
- Retrofitted blown-in cellulose insulation in exterior walls
- Sealed as many air leaks as I could find
- Added programmable [amzn] (and wifi [amzn]) thermostats to set back home temp at night (I bought a 3M-branded version of that wifi thermostat at Home Depot)
- Insulated hot water pipes as far as I could
- Added low-flow shower heads [amzn] & sink aerators [amzn]
And on the increased-use side, we turned the basement into a zoned, heated space last year.
So it’s a ton of variables all working together. How does it look, are there any trends? My best attempt to analyzing that question is to look at therms used per heating degree day during the heating months.
A heating degree day is”a measurement designed to reflect the demand for energy needed to heat a home or business. It is derived from measurements of outside air temperature” according to Wikipedia. I gathered degree days per month from www.degreedays.net (which didn’t perfectly overlap with billing periods, but close enough), subtracted about ten therms from each period (a rough approximation of our water heating use, probably a little low), and graphed the remaining therms per degree day:
We were on a fairly steady decline until about March/April 2011… which is when we put the 2nd heating zone in the basement. Oops! This is what actually prompted these posts; I hadn’t looked for a few months, and when I did, I realized that something had apparently gone a bit wrong in our gas conservation efforts. I’ve since decided to let the basement stay cold unless we are down there; the baseboard radiators heat up in just a couple minutes, there’s no need to keep it warm down there all day long.
Here is the graph of therms per HDD (without normalizing for water heating use) and therms per day as a 12 month rolling average. Around March 2011 looks again like a reversal of the downward trend:I’m not sure if this is really enough data to see a trend – and I’m not quite sure how to properly normalize for weather & separate out hot water from space heat use. This is the best effort so far; I’m open to suggestions!