Those with an add-on furnace....

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jdew1920

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Jan 29, 2008
52
Michigan
did you install a backflow preventer in the plenum of your main furnace?

I've got a new Daka furnace to install. Directions in the manual specifically state to install one in the furnace plenum. Other spots in their documentation don't mention it, I think most people don't add it. Other similar furnace don't specifically require it. The Daka manual does recommend using 90 deg elbows to direct the heated air from the wood furnace upward in the plenum.

If you did use one where did you get it and where did you install it? Our main furnace was replaced a few years ago and it is shorter than our old furnace. The installers basically sat the old plenum & a-coil ontop of a 6" section that they added directly ontop of the main furnace. To add a backflow preventer I would almost prefer to add it below the a-coil since that would give me more room above. I'm not sure what the recommendations are though on where to install it.

I should add that I will be installing with a fan limit control in the plenum to control the operation of the main furnace blower.

I've got 3 cords ready to go (mostly elm) and all I need to do is wait for cold weather and install the furnace.

Any help is appreciated.
 
You will need to install a damper in the plenum. If not you will push heated air backwards, which will get you nowhere on heating. Also when installing the damper, install it above the coil. You don't want the heat to ruin the coil. Also make sure your clearances are okay with the ductwork from the floor above. Also I would not recommend to use your main furnace to help push the heat from the woodfurnace when its on. That cool air from your main furnace will cool the air from the daka alot. Hope this helps. I forgot to add, I would try to get more wood cut. I would start with 5 cords for a winter with a wood furnace.
 
The daka relies on the furnace to move the air through the house. The daka has a 500 cfm blower to get the heat into the plenum - your main furnace does the rest. In my case I have a variable speed blower. I will likely keep it on the lowest setting to help distribute the heat. They do offer a second fan as an option if using as a central furnace. I guess if it turns out to be an issue I can always do that, but from what I have read from others with the same furnace it works well.

How much heat is too much for an A coil? I mean all the heated air from the main furnace goes through it as it is.

If I can get more ready I will but I won't be able to burn 24 hours a day. Based on our gas usage last year & assuming 50% efficiency for the furnace, 3 cords of elm (damn that wood is tuff to split) should supply almost 70% of our heating needs from November through March.
 
jdew1920 said:
How much heat is too much for an A coil? I mean all the heated air from the main furnace goes through it as it is.
Click to expand...

I have raised this question before and I think the biggest concern is the plastic drain pan. The furnace will never put out air over about 160-180F and the plastic can handle this. As long as you are putting the heat in above the coil, I don't see a problem.

Where I forsee a potential problem is if you put the A-coil on top of the wood furnace or otherwise have the heat from the wood furnace going through the coil. In a power failure or other loss of airflow, it is possible for the woodburner to stagnate and really drive up the temperature, possibly melting the drain pan. Admittedly, this is a worst case scenario, but entirely possible.

Chris
 
I have a 2600 sf home and just installed a clayton add on. I used two 90 deg elbows and put them straight into the duct. I didn't do anything to the heat pump that I used last year. I have NO trouble keeping the house toasty! It stays about 78 deg or hotter all the time. I can't choke it down enough.
 
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