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Home built furnace stores heat in rocks
Ronald Behne, Nora Springs, Iowa, has a home-heating system that's most unusual. It consists of a home-built, wood-burning furnace made from a 500-gal. anhydrous tank completely surrounded by rocks.
The 3 ft. dia., 8-ft. long tank installed when the house was built is located in an 8 by 9 by 10-ft. sealed room made of concrete blocks. Behne installed the tank in the room, and completely surrounded it with fist-sized rocks.
"The system saves me more than $500 a year in heating costs each year," says Behne. He uses an LP furnace as a back-up for when he's gone for more than a few days, or when it's extra cold. His gas costs now run from $200 to $300 a year to heat his two-story, 2,700 sq. ft. home.
The unique set-up allows him to fire his home-built furnace with wood for 4 to 5 hours at night and store enough heat in the rocks to last for two days when outside temperature is 20?. When it's 0? (and depending on wind chill) Behne notes that he needs to fire the wood furnace once a day to keep the LP furnace from kicking in.
"I got the idea for my system from heating systems that use water to store heat," Behne explains. "I just decided to use rocks instead."
After placing the tank in the basement room, building the chimney, and filling the room with the limestone rocks, he poured a 4-in. thick concrete roof over the room to both seal the room and serve as fire protection. The side walls are made of 8-in. concrete blocks.
The anhydrous tank has a 20-in. square door for filling with firewood. Heat from the burning wood heats the 3/16-in. thick steel walls of the tank and warms the surrounding rocks in the room. A forced air draft controls how hot the fire burns.
The only opening into the sealed room is the door into the "anhydrous tank" furnace. Keeping the room sealed lets Behne store heat more efficiently.
He burns wood in the furnace but did try burning crop residue. He notes that he only needs to clean out the ashes once a winter.
The air circulation system consists of cold air entering the bottom of the room through two 16-in. dia. tubes. A fan draws warmed air out through a duct on the opposite side of the room and circulates air through the house's duct system. Behne's LP furnace has separate fan and futnace controls. The fan operates at one temperature, pulling warm air out of the sealed room. The furnace is set so it doesn't kick in unless outflowing air isn't warm enough.
Contact: FARM SHOW Followup, Ronald Behne, R.R. 1, Nora Springs Iowa, 50458 (ph 515 749-5808).


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1985 - Volume #9, Issue #5