Propane mystery and comparison of heating fuel saving measures

As I’ve been doing the last few years, I tracked our propane usage this year. It was a rather nasty surprise. We used more this year than last year, despite getting some new windows, a new patio door, and switching from heating the living room to only heating the “library” a couple times a week.

Here are the data. BTW, a “heating degree day” is the unit they use to talk about how cold the weather actually is. (Look them up on the Almanac feature of Weather Underground.) I calculate usage on a gallons-per-heating-degree-day basis to control for variations in the weather.

Gallons of propane Heating degree days Gallons per heating degree day Thermo- stat (away or asleep/ home and awake) Improve- ments in effect this year Comfort
2004-05 892 6126 0.1456 60/66 Programmable thermostat; window plastic
2005-06 719 5545 0.1297 60/66 Turned heat up when getting home instead of
programming; window plastic
2006-07 818 6715 0.1218 55/66 Attic insulation; inflatable flue blocker;
no window plastic
2007-08 844 5771 0.1462 55/66 Window plastic
2008-09 690 6993 0.0987 55/63 Fireplace insert; used on weekends Warmer than last year despite lower thermostat
2009-10 395 6562 0.0602 55/62 Using fireplace more evenings; wall insulation;
window plastic
Need to heat whole house every few days or
55 is too cold at night
2010-11 470 6893 0.0682 55/60 New windows and patio door; no window plastic;
evenings in library
Sometimes chilly; bedrooms warmer – 55 is fine.

The drop between ’04-’05 and ’05-’06 came from turning the heat up manually when we got home, instead of having the programmable thermostat turn it on at the same time every night. See, we have activities a couple nights a week that kept us out of the house until 8 or so…so all that heat was wasted from 5-8pm.

The big drop between ’07-’08 and ’08-’09 came from installing and beginning to use our fireplace insert.  Not only did it provide heat, it also stopped the biggest draft in the house: the unused chimney.  We used it even more in ’09-’10. Notice that we felt warmer with the thermostat set 3 degrees cooler.  I think some of that change was also the attic insulation. We didn’t see any savings the year after we put the insulation in because we were leaking propane at the tank.  I have no idea how much was wasted that year even before we could use it.

In ’10-’11, we replaced some fairly draft 10 y.o. vinyl double-pane windows with Andersens (bedroom, “library,” and kitchen patio door).  I still felt a breeze on my head in bed, though my nose was no longer cold all night. I think the breeze was convection, not infiltration.  We also repurposed the spare bedroom into a “library” with a futon.  We would heat that with an electric space heater several nights a week instead of stoking up the fireplace. Comfort-wise, that heat was not as satisfying as a fire.  We also had an incident where a loose wire overheated and melted and could have caused an electrical fire if we’d not caught it.  The electrician said this was because the space heater was drawing more load than the circuit was really rated for.

Despite all those measures taken this year, we used 75 more gallons of propane this year than last.  The winter was colder, but if we had used propane at the same rate as last year, we would have only burned about 415 gallons this year. So why did we end up burning 55 more gallons of propane?

Here are my theories. I would love to have the input from all you smart people out there.

  • The fireplace and the thermostat are both in the living room.  Last year, when we’d heat with wood, the living room temp would go up from the time we got home until well after we went to bed – meaning the furnace didn’t run at all for at least six hours each day.  This year, when we would heat only the library, the thermostat still thought the whole house was cold, and so the furnace came on more frequently.
  • We didn’t put up any window plastic this year.  The large picture windows in the living room could have lost a lot of heat.  We also didn’t seal the patio door shut this year, so we would occasionally open that door to take out the compost or go to the greenhouse, which lets outside air directly into the kitchen.
  • There’s a leak at the propane tank, or someone stole propane, probably during October.
  • The tank was filled in July ’10.  The decrease in volume between July and October was due to temperatures, not actual propane use, so the reading suggesting we used 20 more gallons of propane between May and October this year compared to last is spurious. (That still leaves 35 gallons to account for.)
  • The pattern of when it was cold is as important as how cold it was.  We had a much colder Nov/Dec this year as compared to last…but supposedly, from May-Oct it there were far fewer heating degree days this year (803 vs. 1130).
  • There’s some weird thermodynamic benefit to really heating the house thoroughly once a day. (This sounds like hokum to me.)
  • It was much less sunny this year and we got less solar gain, especially in the living room.

What seems most plausible to you?  Got any other ideas?



  1. April 29, 2011 at 7:22 pm

    One thing you wrote jumped out at me: draft on your head in the bedroom. I have no idea whether this will appeal to you, but…I’ve been a poor sleeper my entire life. To cope with this I’ve used earplugs since forever, and about ten years ago I picked up a sleeping mask routine. It started with those jaunty little fleece headbands sold to skiers in lieu of the less cool earmuffs. I started wearing one of those, but pulled down over my eyes. When I lost a couple of them during travel over the years, I just bought fleece by the yard and hand sewed myself a replacement. It not only shuts out light, which was my original purpose, but now in our chilly bedroom it keeps my nose and ears warm too. I love it. So long as the blankets are heavy and my nose is warm I don’t care how low the temperature gets. You might try it and see if you like it. For extra light blocking in summer when sunrise is so early, I tuck a folded handkerchief under the fleece, so light doesn’t creep through the gaps. (What can I say? I’m a really lousy sleeper.)

  2. sqwook said,

    April 29, 2011 at 11:07 pm

    My thoughts on the theories:
    A. I think this is a big one.
    B. I think this may matter as pertains to the thermostat.
    C. Seems unlikely.
    D. Possible I suppose.
    E. But you wouldn’t even have the heater on much in May-Oct, right? So even if it was warmer, that wouldn’t matter. Or are you saying it was colder May-Oct? I don’t see how May-Oct would effect much, whereas a cold Nov/Dec would. Keeping the house 55 when it’s 55 outside is no big deal; Keeping it 55 when it’s 20 is.
    F. Hm.
    G. Solar gain – not sure how much it factors. But all its factor does effect the thermostat, so…

    tl;dr – Thermostat is ringing the most true to me. Because when the living room was warm, you went to bed & snuggled under covers, and the heater didn’t come on until hours later.

  3. Geomom said,

    April 30, 2011 at 8:57 am

    I think it was most likely due to the thermostat issue, with contributions from no plastic on the living room windows. We have a wireless thermostat, which can be moved from room to room, maybe you could try something like that if you plan on sticking with the library plan next year.

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