"Grabber' Captures Wasted Chimney Heat

"Grabber' Captures Wasted Chimney Heat WOOD STOVES/FURNACES Wood Stoves/Furnaces (20L) 30-6-34 Anders McGriff says his "stack enhancer" grabs heat that would otherwise go up the chimney on his wood-fired boiler. The water jacket simply wraps around the flue and is plumbed into the boiler. "I was running such a high flue temperature that I was having chimney problems," says McGriff. "I ran the furnace hot to keep an old 3,000-sq. ft. farmhouse heated plus my 40 by 70-ft. shop with its 19-ft. ceiling. With the two forced air fans on the firebox, it was like a blast furnace, and the 8-in. pipe going to the chimney would turn red several times a day." McGriff figured his stack was running 700? and higher and was rarely below 500? even when the fans were turned off. He used an 8-in. dia. piece of well casing to replace the flue and fitted a 10-in. dia. piece of 10-gauge pipe over it, giving him 1 in. of water around the pipe. "I ran cold water return lines from the house into the bottom of the stack enhancer and out the top and then into the stove's water jacket," says McGriff. "Normally the hot water going to the house runs about 170? and comes back cool. The water comes out of the stack enhancer at about that 170? temperature." After using the unit for a year, McGriff disassembled it and found very little creosote, even though he often burns waste wood, not premium dry firewood. "I disassembled my entire chimney as well, and in 15 ft. I only had enough creosote to fill a cigarette pack." McGriff built a similar unit for Dave Devito, a nearby plumbing and heating contractor. Devito reversed the water flow, running the cold water in the top of the jacket and out the bottom, seeking to capture additional heat gain, but doubts it matters. Unlike McGriff, Devito burns ear corn. "Before I added the stack enhancer, the stack would reach 800 to 900 degrees F. on a peak burn," says Devito. "With the enhancer, I never saw it above 500 degrees." Devito installed a pop-off pressure release valve on the stack enhancer. He also added temperature sensors to measure flue gas temperatures and incoming water. "Before installing the stack enhancer, I had to fire my boiler three times a day on ear corn," says Devito. "Now I get the same amount of heat with a 12-hour burn, at least until it gets below zero. I figure it costs me about $100 a month to heat my farm house and provide enough hot water for my family of seven." Devito agrees that maintaining sufficient flue temperatures to prevent creosote buildup is important. "A flue temperature of 400 to 500? or even 300 to 500? with dry wood, is plenty to keep the stack clean," he says. "Most wood boilers are still pretty crude, and you lose a lot of operating efficiency. This gets some of it back." Contact: FARM SHOW Followup, Anders McGriff, McGriff Welding, P.O. Box 476, Braham, Minn. 55006 (ph 320 679-1780).

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