# Rectangular duct damper installation help.



## awjacks24 (Nov 20, 2015)

I have a wood furnace that ties into the electric HVAC in my basement. I had the chimney sweep over today and he suggested rerouting the air supply for the wood furnace to make it more efficient. 

Right now the wood furnace draws air from the return and it gets sucked (hopefully) into the warm air side of the supply duct after the filters. This is not very efficient and causes the cooling fan on the wood furnace to run constantly, running up my electric bill. 

What I want to do is run the heat from the furnace back into the return and install a damper between the intake and exhaust ports in the return so that the HVAC fan will draw all air through the wood furnace when it is burning. This will also ensure that the air from the furnace is getting filtered. Achoo!

The return duct is 18"X11.5" ID. and I is sealed so I will have to cut an 8" hole for the hot air duct from the wood furnace and then somehow get an 11.5" wide piece of sheet metal through to act as my damper. How should I go about this? I'd like to keep it DIY. Drawing for clarity. Any help is greatly appreciated.


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## nealtw (Nov 20, 2015)

The bottom of that duct will come apart so you could set your damper just above the joist and cut your hole in that bottom section. If I understand it correctly.
You might find this good for some hints.
http://www.thisoldhouse.com/toh/video/0,,20504377,00.html


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## awjacks24 (Nov 20, 2015)

Well, actually I'm wanting to run the 8" round duct on the right side of the wood furnace to the rectangular return duct at the right side of the photo and then install a damper between where the one round duct comes from the return up top and where I run the heat back into the return. What I'm hoping to achieve is a better draw through the wood furnace which has a thermostat controlled blower fan which keeps the unit from over heating. The problem is that the thermostat only goes to 120° F and because the HVAC system isn't actually pulling the air through the wood furnace, the blower is constantly on and running up my electric bill.


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## awjacks24 (Nov 20, 2015)

The thermostat measures the temp around the fire box, not the temp in the house.


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## nealtw (Nov 20, 2015)

Ya, I don't know how you can beat that.


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## nealtw (Nov 20, 2015)

There is thread on wind turbines, depending on the size of the hydo bill you might find this interesting.
http://www.houserepairtalk.com/showthread.php?t=19762


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## awjacks24 (Nov 20, 2015)

Thanks. I don't own the house. Electric bills last winter were only up to $350/mo. So I'm not looking at alternative energy yet. Although the chimney sweep was talking my ear off about his solar system at his home.


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## awjacks24 (Nov 20, 2015)

He said he has his wood furnace system set up how I want to do it and it really cranks out the heat.


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## nealtw (Nov 20, 2015)

The fan running will be cheaper than the electric furnace.


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## awjacks24 (Nov 20, 2015)

Maybe. The wood furnace is probably 30-35 years old and the electric one is only 8.


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## awjacks24 (Nov 20, 2015)

Plus it's probably not strong enough to push air through the whole house.


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## nealtw (Nov 20, 2015)

They both have a fan.


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## nealtw (Nov 20, 2015)

hmmmm................


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## frodo (Nov 22, 2015)

make a slot in the duct,  make a damper to slide in and out,  use door sticky tape to seal


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## frodo (Nov 22, 2015)

most fans in your ac unit are 3 speed.   look in the unit for the wires coming off the fan

3 wires  blk is high speed, blue is medium, red is low,  should be a bundle with those 3 colors

yours is most likely hooked to blue,   switch to blk


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## awjacks24 (Nov 22, 2015)

Thanks, Frodo. I was thinking something like that for the damper. 
The Do I need to turn up the AC fan speed because I am diverting the air?


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## awjacks24 (Nov 22, 2015)

I hadn't gotten as far as using rails as a guide though. That's a good idea.


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## nealtw (Nov 22, 2015)

With the 2 different size ducts you may want to block only part of the air off


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## awjacks24 (Nov 22, 2015)

Good thought. I will make the damper so that it is variable.


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## frodo (Nov 23, 2015)

if you really want to get fancy

http://screencast.com/t/BR8FoHww


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## awjacks24 (Nov 23, 2015)

Where's the fun in that? I don't think that they make them for return sizes anyways. I haven't seen that size anywhere.


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