Making efficient use of logs in a wood burner or boiler is good stewardship. It saves money and labor on firewood. It means less labor since a smaller amount of wood will burn cleaner and longer. It reduces the likelihood of complaints from neighbors who are downwind of an inefficient stove. Everyone wins.
A few simple steps can help assure your wood-fired system is efficient and effective.
For maximum efficiency, Mark Odell, vice president of sales at Econoburn, Brocton, New York, recommends keeping an adequate coal bed established in the upper chamber while adding only a few pieces of wood at a time. “This causes the boiler to gasify more and prevents more heat than is necessary from being transferred to the water jacket,” he said, noting that this works well when you’re home for the evening. “It can reduce the overall amount of wood that you use by a few percentage points.”
There are a lot of other things an owner can do to help the stove do a better job. For one, avoid burning trash. Plastics, especially, will clog up the orifices. For another, have a certified technician check the wood boiler regularly.
Checking chimney height is a favorite recommendation of Rodney Tollefson, vice president of Central Boiler, Greenbush, Minnesota. It is one of the best ways to assure proper functioning of a burner. “It is most important that exhaust is released at a high enough level to get it above nearby buildings,” he said.
When firing a boiler from scratch, Odell recommends using dry kindling and leaving the bypass damper open for about a half hour. This gives sufficient time to establish the coal bed above the refractory nozzle, which will in turn yield the most efficient gasification. “We do not recommend leaving the boiler off and the bottom door open to get your fire going faster,” he cautioned.
In the event that you leave the boiler and forget to close the door, the fire will grow to the point that the boiler overheats and produces steam.
Hot, hot, hot
On the other hand, if you are having problems with heat output, Odell recommends checking check the moisture content of your wood. Decent firewood moisture meters are available for under $30. They can save a lot of time and energy spent troubleshooting an easy-to-remedy problem.
“We cannot overstate the effect that the moisture content of your wood has on the overall performance of your boiler,” Odell said.
“Use good, dry, seasoned wood,” Tollefson agreed. Old hands recognize the “thut-thut” sound of unseasoned wood contrasted to the sharp “chink-chink” seasoned wood makes.
New York approves the use of seasoned clean wood; wood pellets made from clean wood; heating oil in compliance with Subpart 225-1, LP gas or natural gas that may be used as starter fuels; and non-glossy, non-colored papers (including newspaper) only to start a woodburner.
Do burn good quality hardwood. Wood that has been dried below 20 percent moisture – 15 percent is best – will do the job well. Use of dry, seasoned wood also helps prevent the buildup of creosote.
“It takes 30 percent more unseasoned wood to produce the same amount of heat as seasoned wood,” Tollefson said.
In most states, burning garbage, unseasoned wood, wood containing preservatives or other coatings, tires, household chemicals, coal, yard waste (including lawn clippings), plywood and animal carcasses is forbidden.
Another no-no, Odell stated, is using excessive amounts of wood that is cut into tiny pieces. “This can generate an intense coal bed that could overheat your boiler,” he said. Instead, if you have a lot of small scraps to burn, mix them with regular chunk wood.
If your stove is not the latest-and-greatest model, look at any of the newer systems when replacing it. There is no reason, however, to rush out and buy a new system if the old one is working efficiently.
In some cases, an owner may be encouraged to replace the burner with a newer certified model or a different type of furnace. That is probably a better option than kludging together a retrofit system on an existing, older-model stove.
Tollefson said they have little faith in retrofits. “It’s not feasible to expect them to work long enough to pay off,” he said.
No matter which direction you take, having dry wood will pay off in heat production. The theoretical heat value of perfectly dry wood is a touch under 8,000 Btu per pound. That, however, assumes the wood has been dried to zero moisture.
More typical would be wood that was cut one season and left to air dry under a tarp or shed for a year. That wood would typically go into the stove at about 20 percent moisture. If this sounds high, keep in mind that stored field corn usually is kept around 15.5 percent moisture – not much different.
That 20 percent wood will give about 6,100 to 6,150 Btu per pound output. Burning drier wood means having to burn less wood for the heat output and, in the long run, will save both dollars and the environment.
Lastly, keep the ashes cleaned out of the combustion chamber. Odell recommends that ashes be removed from their stoves about twice per week in order to keep the efficiency high.
Cover photo: KatarzynaBialasiewicz/istock