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Furnace to circulate heat from woodstove

I know that furnaces can be set up with a switch which runs the fan even if the burner is not on. Would it be possible to use this feature to filter,humidify and circulate heat from a freestanding woodstove if the cold aif return was in the room with the woodstove?

Asked by Anonymous
Posted Fri, 01/01/2010 - 17:43
Edited Sat, 01/02/2010 - 06:03

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7 Answers

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1.
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Only if the woodstove significantly overheats the room. Wood-heated air will rise to the ceiling while cold make-up air, drawn in through cracks by the negative pressure created by the chimney/flue, will pool on the floor. If the return register is on the floor, then it will draw cool air and circulate it through the house.

You would need a return grill at ceiling level above the woodstove, and hope that smoke leakage when the door is opened or the smell of overheated metal and burning dust does not get distributed throughout the house.

Answered by Riversong
Posted Fri, 01/01/2010 - 21:28

2.
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Will,
If I understand your question correctly, you don't really want a free-standing wood stove. You want a wood-burning furnace. Many manufacturers sell them.

Answered by Martin Holladay, GBA Advisor
Posted Sat, 01/02/2010 - 06:01

3.
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I am going to have a fossil fuel furnace and I am going to have a woodstove for power outages and to use open like a fireplace. I just wondered if anyone had any experience circulating heat from a woodstove with a furnace fan and ducts. Another option I'm considering is inexpensive through the wall fans. Mr. Riversong brings up some good points about air quality and the location of the return ducts.

Answered by Will Goodwin
Posted Sat, 01/02/2010 - 14:58

4.
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I've been using my heat-pump air handler to circulate warm air from my wood stove throughout my house for years. It definitely makes a difference and I recommend it. It won't equalize the heat, the living room is still much warmer than the bedrooms, but it warms the bedrooms a lot more than they would be without the blower running and it helps keep the living room from over-heating which is an issue in this well-insulated home.

However, if your duct work is outside the heated envelope then you definitely don't want to do this and if you need a humidifier your house is too drafty and you need a blower door and duct blaster test .

Answered by Michael Chandler, GBA Advisor
Posted Sat, 01/02/2010 - 16:13

5.
Helpful? 0

You don't mention what climate zone or geographic area you're in. But running a woodstove open "like a fireplace" is almost not quite as inefficient as a masonry fireplace but far less efficient than an EPA certified woodstove with the door closed as intended.

Many quality woodstoves have glass doors to offer the aesthetics of an open burn without the efficiency liability. Increasing the flue gas volume with open doors will also increase infiltration and contribute to dry house syndrome.

Answered by Riversong
Posted Sat, 01/02/2010 - 20:26

6.
Helpful? 0

Will, the answer to your question is yes. I've done this many times and it can work fine. First, if your stove is equipped for it, you should install a direct combustion air duct. The return air intake grill to the furnace should be located at the ceiling or ridge in the room with the woodstove, and the blower in the furnace wired to a separate thermostat to turn on with a temperature rise above some temperature, say 75 degrees. (This "cooling" thermostat should be located close to the ceiling, must control the blower only, and must be separate from the room heating stat.) This will distribute the air to all zones on the supply side of the furnace, and will also filter and humidify the air to some degree. Use the best filters you can and make sure the woodstove is working properly to minimize smoke and fumes. Consider installing a smoke detector in this room and also a line voltage cooling stat at the ridge set at a high temperature to shut the furnace blower off in case of a fire.

Answered by Pete Powell
Posted Sun, 01/03/2010 - 22:38

7.
Helpful? 0

I am involved in a Design Build project in Michigan and we are looking at incorporating this concept as part of an overall energy reduction strategy. Our client also expressed an interest in this idea so in the event of an extened balck out condition he will have heat. The problem with this concept is that if we loose power from the grid, we loose our HVAC system unless we have a PV (non grid connected) to run the furnace.... something to consider.

Answered by Lance Bowen
Posted Sat, 01/16/2010 - 06:46

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