Islanders have always had to pay a little more for fuel than mainlanders but the steeply rising cost of heating a home is forcing year-round residents to consider alternatives to fuel oil and propane. On Islesboro, woodstoves are commonly used as a secondary source of heat, supplementing a fossil-fuel fired central heating system. Within the last several years and even before the present, alarming rise in home-heating costs, a new type of wood-burning furnace arrived on the island. Now several families are using the system as their primary source of heat.
The wood-fired furnace has been around for generations but the outdoor wood furnace that heats an entire home is a fairly new concept. According to its advocates, burning wood in a furnace outside the house is cleaner, burns longer and is safer than a conventional woodstove. The furnace stands on a concrete slab, has corrugated steel sides and a gambrel roof that makes the unit look like a tiny barn or a high-tech outhouse. A cylindrical flue protrudes skyward. Standing next to this unit, one wonders how burning wood outside is going to heat a house 50 feet away.
The fire in the furnace heats water, which is pumped through insulated pipes buried in the ground between the furnace and the house. The heated water circulates through a heat exchanger installed within a home’s central heating system. Existing hot water baseboards or hot-air ductwork distribute heat to the same rooms that were heated prior to the installation of the outdoor wood-burning furnace.
The old furnace remains an integral part of the system and may burn oil or gas as a secondary source of heat. A thermostat located in the door of the outdoor furnace opens or closes a vent that allows air into the firebox and automatically controls the burn rate. The firebox is so big that one large load of firewood should be sufficient to heat enough water to keep a house comfortable for up to three days.
The outdoor furnace is pricey – around seven thousand dollars – and that’s not including plumbing costs. A reliable source of firewood is essential. The furnace could take up to a four-foot log but these logs have to have a sizable diameter to burn for a reasonable length of time and loading a furnace with heavy, long logs can be a challenge. Though wood-furnace owners often gratefully accept logs that remain after a forest-clearing project, the labor involved in transporting them can be time-consuming and include its own costs. Furnace-owners seem to prefer spruce logs cut in three-foot lengths. This arrangement works well for homeowners who thin their woods, clear a building site or create a water view but who can’t afford to hire a logging truck and skidder to haul the limbed trunks away.
A furnace will burn clean wood waste of all types. Scott Rolerson, a carpenter, bought his furnace four years ago. He burns demolition material like decking, old stairs, posts and cedar shingles, but never anything that’s pressure-treated. He has his eye on a piano that’s been standing by the side of the road up-island but is wary about all the metal inside. He acknowledges that it’s easier to supply an outdoor furnace if the owner has access to a tractor and dump truck, and that it does take some muscle to feed the thing. Scott was at a mainland fair where an outdoor furnace salesman was hawking the virtues of his product. A potential buyer – his wife standing at his side – said that he might consider a purchase if his wife here could help maintain the burn. The salesman studied the woman before him and confessed, “You might need a bigger wife.”
The outdoor, wood burning furnace can be a vast improvement over earlier methods of heating. Some winters ago, two islanders were trying to heat a garage with a woodstove homemade from an old fuel oil tank, but their wood supply was damp and green. The stove rejected the inferior fuel, hissed, smoldered and refused to cooperate.
The men knew that car tires burned well, having used them to ignite brush piles, so they thrust a tire into the stubborn stove. It burned well; alarmingly well. In a minute the tire was burning so furiously that the supercharged stove was red hot. Frightfully thick, black smoke belched from the stove pipe and chimney. As the inferno reached its climax, the men hastily collected tools and car parts to save from destruction in case the whole building went up in flames. In their panic, the two wondered aloud if they should call the fire department but the tire consumed itself soon enough, the exhausted stove cooled and the specter of public witness to the near-disaster faded, much to the relief of the two islanders, warm now, but humbled by the ordeal.