Thanks for the information about alternative ways to look at my energy use and ways to reduce it. A colleague suggests we find a way to convert heating energy, cooling energy, and other home energy loads into gallons of gasoline! Then we could say "My house gets 1,500 gallons per year. What about yours?" It would be a way to mark your energy efficiency that everyone could understand.

Nancy, the first thing I thought of when I read your post was "that house must be a sieve." I'm not basing that on anything as sophisticated as a Manual J analysis, but on a feeling that, in most cases, the furnace is plenty big. There are people living in houses in Northern Germany (called Passive Houses) that are so well insulated that they only use a furnace or water heater to heat their home on the very coldest of days, if they even have a furnace. Body heat and the heat from lights and appliances is enough most of the time. Of course, if you have your home air-sealed and well insulated you have to make sure that for health and other reasons you are getting enough fresh air and that you can still move moisture out. Some kind of controlled ventilation strategy is a must.

So I'd suggest, Nancy, that you have a home performance contractor come out and do an energy audit of your home. You can go to the Home Performance with Energy Star Web site and find a local, certified contractor to do the audit. Best of luck!

http://www.energystarpartners.net/ia/Water_heaters/Documents/WHPAGette_Final.pdf

I refer you to the bar graph on page 16 (p.22 of the .pdf.)

This makes sense- the reservoirs are at their warmest at the end of the summer, long after the snowmelt. The ground at distribution piping-depths is similarly at it's warmest at the end of summer. Then by the end of December the ground is cooler, and the reservoirs have radiated an enormous amount of heat into the sky.

So, to figure the actual HEATING component of your fuel bills you'll have to insert monthly or seasonal fudge-factors to get it right. In 8000+ HDD climates the hot water factor disappears into the noise, but in coastal northern CA's ~3000 HDD climate hot water heating represents a much larger fraction of the total.

I live in a 3 person household in central MA in a ~2400' house. The combined heat/HW/cooking runs ~8.5BTU/HDD/ft2 after tightening up & insulating our 85 year old wood-framed structure a bit. I know of several houses (both younger & older) that use twice that. There's plenty left to do- shouldn't be too difficult to get it under 5BTU/HDD/ft2, if I look at the necessary upgrades as 10 or 15 year investments in both creature-comfort and fuel cost savings. YMMV

But is BTU/HDD/ft2 really the right metric? A 3 person household in a fairly tight 5000' house burning 5BTU/HDD/ft2 is already burning more than we are.

Nancy: Do a Manual-J type of heat load estimate to figure out the "right" size of the heating plant. There's a pretty-good freebie software package downloadable here:

http://slantfin.com/heat-loss-software.html

If 15F is normally one of the coldest temps you see in a typical heating system, and your furnace is running more than 50% of the time, it's probably in the right ball-park. If it's running 100% of the time and continuing to cool off inside, it's definitely undersized. But that would be rare- Manual-J calculations tend to overestimate by ~25%, and heating contractors tend to then add some margin, then round up to the next larger size, so 100% oversizing (or more) is common. The net result of oversizing is higher fuel bills and rapid cycling (you first feel too cold, then it blasts you to a sweat, then an hour later it's feeling chilly again, repeat.) It's far better to do the heat load calculation and UNDERsize it by 15% or so- you'll be more comfortable through most of the season and pay less. If it doesn't quite keep up during an extended cold snap, simply leaving the lights on or intermittently using space heaters in the most-used rooms is usually cost effective. (Most of the time the "design day" coldest temperatures occur at night, when you're asleep under the covers anyway.)

Nancy Law