Sunday, October 12, 2008

Home heating economics (firewood and other contemplations)

In our house we have central heating and air. We have not yet turned on the Air conditioner, and we probably never will.

Heat for this house has in the past been supplied in many ways. Once, there were wood stoves. Then, there was coal. Coal was replaced by fuel oil. Fuel oil has given way to propane. Propane again gives way to wood.

The current central heating system for the house actually consists of 2 propane furnaces working in harmony and controlled by a multi stage thermostat. One of the furnaces alone does not have sufficient power to heat the house, especially the upstairs. Most of the reason for this is that we have large lengths of ductwork that runs through crawlspaces and the basement, all of which was uninsulated and leaky when we moved in (we also have drafty single pane windows... that's a story for later). When we moved in, the secondary furnace was not operational. As a result, it took about 2 hours for the furnace to begin delivering warm air into a cold house. we always knew where our mittens were. The basement was warm though, and the ducts radiated much heat! Owing to the lack of insulation, in rooms serviced by long runs of ductwork the air blowing out would never be "warm".

After getting the second furnace operational, magic things happened - if you throw enough brute power into things, we get cooking quite quickly! The furnace was fixed on a very cold day, but the house heated up like magic! Two furnaces firing heats the whole house quickly. Of course, wonderful things can happen if you are willing to burn 50 gallons of propane in a day!

This number is real - we burned 50 gallons of propane in a single day. This explains why the average use of propane by the previous owners was 1800 gallons per year!!!! Propane currently costs 2.69 per gallon. I have no interest in spending $5,000 to heat our house this year. Fortunately, I don't think we'll have too.

We stayed chilly for most of last winter, and between mid January and now we have used 600 gallons of propane. We did manage to insulate 80% of the ductwork (Makes a big difference). We also lined some of the windows with plastic shrinky wrap lining (Huge help there!!!). JoAnna also made curtains for the bedroom (kills those drafts quite nicely!). INstallation of a new programmable thermostat was also a big plus. Despite all of this, I still feel as though we're probably getting less than 50% efficiency out of our 80% efficient furnace (we only turned one on for most of the season). Lots of heat wasted still.

Fortunately, we have wood, and 2 stoves to burn it in.

I recently surveyed the trees of our property, here is what I learned:

Our property is slightly more than 8 acres, half of which is a field. The remaining half has trees. I measured every tree on the property with a DBH of greater than 4 inches. We have 438 trees of this size. There are an additional 3-400 saplings of 1-4 inches DBH. The average DBH of the trees on our property is 9.6 inches. The largest tree that we have is a Silver Maple with a DBH of 43 inches. The second largest is a Sugar Maple with a 36" trunk. We have 197 significant Black Walnut trees, 28 of which have a DBH of > 16 inches. The predominant species on the property include Walnut, Sugar Maple, Black Locust, Cherry, and Mulberry.

After reading material from a variety of extension agencies, I am estimating that our trees make up about 115 cords of wood. I am also estimating that 4 acres of woodlot trees can produce 2 cords of wood per year.

Here are some other fun factoids:

1 gallon of propane = 14.6 pounds of wood.

1 cord of walnut = 218 gallons of propane. A cord of Black Locust is the BTU equivalent of 275 gallons of propane. A cord of our least favorite tree, silver maple, is only 188 gallons of LPG.

Let's normalize these somewhat and assume that we want to burn the equivalent of 750 gallons of propane per year - this approximates to ~3.1 cords of firewood, give or take. In the extension materials that I have read, this seems like a reasonable amount of wood and is in line with the experience of others. This may be beyond the sutainable yield of our woodlot though, by about a little more than a cord per year. In 90 years, our woodlot will be a field of stumps. Lesson learned - We have enough wood for our lifetime!

We want to keep trees though, so we need to take a sustainable yield.

So this year, I would like it very much if we did not have to use our central propane furnace at all.

This spring we dropped 4 trees that were interfering with our barn, as well as a large dead walnut tree. We also chopped up a large Sugar Maple that fell in a severe thunderstorm. Our labor earned us a little over 2 cords of walnut, locust and maple, ready and waiting for the first chilly evening. I don't know if 2 cords will be enough to make it through the winter, but I have to believe that anything is better than burning propane in our central furnace, including space heaters.

A 1500 watt space heater will do an acceptable job of heating a room. Left on for 8 hours, it consumes 12 kilowatt hours of electricity. We pay $0.07 per kilowatt hour (for now...). This translates to 84 cents per day per space heater. Even if we run 3 heaters 8 hours each per day, we are still looking at 2.52 per day, or about an extra 75 bucks on our electric bill each month. Even if we doubled that to be an extra 150 bucks per month, and assumed that we ran them for 6 months, we're still looking at less than a thousand dollars worth of electricity. I wonder how this compares to the cost of electricity for the blower on the furnaces. In the winter with the furnace, our electric bill last year was over 200/month. In the summer, it has been 80-100 bucks per month. The only thing not on now is the furnace...

This, coupled with our wood stoves seems the way to go. As fossil fuels become more and more scare, we need to go full circle, back to wood stoves, the way this house was heated when it was built, 152 years ago.

Anyone wanna buy 2 propane furnaces and an A/C compressor?


  1. One more thing - I'm not cutting down any of the Sugar Maple trees. Those are for syrup, not firewood...!!!

  2. I have also done this math and found the blower on a furnace to be a huge user of electricity. We also have a 60,000 BTU/hr wood stove, but we have a smaller house and if it is burning full bore we have to open the windows. I agree we need to go full circle and burn wood, but we must be careful and not go backwards. My new woodstove burns 75% efficient and we only use 3 cord a year (thats face cords). If we are to depend on wood for heat we MUST maximize efficiency and reduce particulates.

  3. True dat. Efficiency = good. Have any thoughts on catalytic vs non-catalytic stoves?

    We have yet to experience the full firepower of our stove - it was 85 degrees here yesterday!!! Lit our last break-in fire a couple weeks ago when the temp dropped into the 30s.

  4. Many old timers will tell you that a catalytic converter just makes a lot of creosote. I think the most important thing to do to keep high efficiency is burn good wood at the right temp.

  5. They make fans that run on the heat of the stove....look it up! Free...Mom B

  6. Whoa - lots of thought process going on here. I know my parents switched from oil to wood in the seventies after they spent $1800 or so on oil during one heating system. They started with a franklin stove, put in new insulation, windows, eventually moved to a Vermont Castings (which has been there as long back as this young lad can remember). When I was a kid, we would take the tops left behind by loggers who were only interested in the trunks of trees. Since college, my dad's been buying log loads 15 ton at a time for about $600. You need to factor in the time it takes to cut up, split, stack, gas to run the saw, and splitter (if you're not doing it by hand). I won't get into the larger picture of trees/energy consumed to produce the heat for your house vs. what you could/should plant to offset that.

    Shamed to admit this for someone who has been around a wood burning stove his entire life but I have never had a clear picture of what a cord or face cord amount to but 2 cords of wood as your sole/primary source of heat seems low. I am going to suggest Dad take a look at this posting and see what his reaction is. I know Chris has a super efficient stove compared to the Vt castings my parents have and he does burn a lot less wood but, rough guess, he is also heating a lot less space and his house is well laid out for heating by one fairly centrally located stove.

    I think I am rambling now so am going to sign off.

  7. I have seen those fans that work off the heat of the stove. I think they are great!

    In terms of the math, I think Bill is talking full face cord, while most people here in CNY usually refer to face cord. So when Bill says he will burn 2 cord he means 6 cord, while I burn about 3 cord and your dad about 10.

    I think your Dad's Vermont Casting's is probably a lot higher BTU output than ours, too. And say for argument's sake its 60% efficient compared to our new stove's 75%. If we have 1600 sq ft, JoBi has 2600 sq ft and your parents about 2600 sq ft then the math all works out.

    In terms of the carbon balance it is important to remember that burning wood is carbon neutral here in the northeast where forested land has been increasing since the 1800s (Lots of water and wood, the NE rocks). It will likely be carbon neutral even if twice as many homes start heating with wood.

    What IS concerning about a lot of homes heating with wood is air quality, and I think the only thing that can be done about that is efficient stoves and a good high burn temp.

    I am a big fan of those new outdoor wood boilers, anyone check those out?

  8. Yeah, I mean 2 full cords. This probably occupied the better part of 5 Saturdays to chop, split, haul, stack, and then restack. I used about 2 gallons of gas in the chainsaw this year and dulled 3 blades. Time to get a file.

  9. you got a neat site here, and i could not help but chime in. Last year my familiy began heating with as, for to continue with propane would have been $6,000. we burned ~16-20 full chords (4ftx4ftx8ft). granted, halfe of this was poor quality. this year i have bucked, split and stacked 12 full chord consisting almost exclusivly of maple and shagbark hickory. We burn some wood! But it gets cold in Michigan.