Now that winter's grip is finally letting go, I thought it would be a good time to look at our firewood usage for the first heating season in our new straw bale house.
To be honest my records are not 100% accurate. The house is not fully insulated so I was a little lazy keeping track. Some of the wall cavities surrounding the straw bales are still void of their full insulation and the chimney chase is only partially insulated. The (2 year) temporary exterior doors are leaky and we heat with an old inefficient Kodiak wood stove (aka Smoke Dragon) from the 1970s. With those shortfalls and others to consider, this recap will only give us a general idea of how well a straw bale house can perform in cold upstate New York. From there we can project how efficient our house will become as we make our final improvements.
Our heating season began sometime in late September (or was it early October?). We started by burning red oak that had been laying around for a couple of years. It was bucked but never split. Once in the wood stove it sizzled, foamed, and sap poured from the end grain of each log. Those precious little BTUs were wasted boiling off sap instead of heating the house. It was frustrating and a waste of time. Even more frustrating was I knew red oak needed to dry at least 2-3 years after being split. The old timers use to refer to red oak as "piss oak" and now I do too.
Still early in the season I wasn't too worried about the firewood situation since most fires were lit only to take the chill from the air. But before long the reality of our dismal firewood situation was up against colder weather and we decided to buy firewood. It pained me to do so since we're surrounded by trees but I swallowed my pride and picked up the phone.
To date (April 14) we have burned about three and a half cords of wood. Two of those cords we purchased and the remainder came from our unseasoned pile and the standing dead trees I've been cutting down recently to get us through the final weeks of the season.
To put this in perspective I started by using a simple Home Energy Calculator to show how many BTUs per square foot we used. The btu/square foot calculation seems to be the industry standard home heating and/or total home energy consumption metric used by the Energy Information Administrativeand groups like the Passive House Institute US.
Since wood is our only active* source of heat the calculation was simple.
3.5 cords of wood at 22,000,000 BTUs/per cord = 77,000,000 BTUs
77,000,000 BTUs ÷ 2,400 sq. ft. = 32,083.3 BTUs/sq. ft.
While 32,083.3 BTUs/sq. ft. is better than average it's nothing to brag about. From what I could find on the internet, the average home in the Northeast and in New England uses anywhere from 40,000 to 50,000 BTUs per sq. ft. The Passive House Institute US sets their qualification threshold at 4750 BTU/sq.ft. a year. That's a 27,333 BTU difference. Ouch.
Not to worry. Our intention is to finish insulating, build better doors, and if the stars align, build a masonry heater (I recommend the picture gallery) later this year. The masonry heater alone will drop our firewood usage by more than half. The goal is to use only one cord per year. That translates to only $240 for an entire year of heating...that's if we have to buy firewood again (harumph).
Overall I am pleased. I know some people who typically use far more wood with less square footage. I'd be interested to hear from others with their results...wood, oil, propane, solar...doesn't matter, I'm curious. Keep me posted.
Happy Spring! *We do get a slight amount of passive-solar heat gain. During construction I hesitated removing the trees from the south side of the house in fear of over-heating in the summer. It turns out my roof overhang calculations were spot-on for shading so I'll drop the trees, use them for firewood, and hopefully see more passive heat gain next year.