# Build a plenum for outside air intake?



## ikessky (Sep 2, 2008)

Hello all.  I've been looking around the site for a few days and am really pleased at the amount of info here.

I purchased my house a little over a year ago (although I've lived in the house for a few years already!).  It is a ranch style with a full basement and a two-car attached garage.  We have a Lennox Pulse gas furnace that we've heated with for the past few years and I'm getting sick of the high energy bills in the winter time.  It is the only gas appliance we have and I'm looking to get off the grid a little bit.  In looking things over, I realized that we already have a chimney, although I'm not sure the condition of the flue as the furnce vent pipes are run up the chimney and I have yet to remove them.  I know it's not a big deal to stainless steel sleeve the chimney, but I'm hoping the flue is just fine.  Anyway, we purchased a Daka add-on furnace that I plan to install as a supplimentary furnace.  The heat output will go into the upper plenum on my gas furnace and be distributed via my current duct work.

Here is where my question really begins.  The gas furnace has an intake for outside air and a cold air return system in the house.  Would I be better off to make a plenum for outside air intake so that I could feed my wood stove and my gas furnace?  Should I just take a run from the cold air return to the wood stove blower?  Or should I not do either and just leave the fan open to the basement air?


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## begreen (Sep 2, 2008)

The firebox air supply and the furnace air intakes are independent needs. Can you describe how the Pulse air intake is currently set up? At this point I am not sure which Pulse this is. Is this a conventional 80% efficiency unit with a large metal flue connected to the chimney? Or is this a high efficiency condensing furnace with PVC exhaust and air intake? Without seeing the setup my advice would be to not disturb the Pulse furnace outside air. But more info would help. If you decide to install a fresh air supply for the Daka, space it at least 18" from the Pulse air intake. As far as the exhaust, I would not have them tied to a common flue. They should be independently vented. If the Pulse is using the chimney, then it may need to be power vented. 

The add on furnace will perform better if it is correctly tied in to the supply and return plenums. The Daka manual is a bit confusing and basic. You might want to look at the manual for the Yukon add-on furnace for a better pictorial description of a proper installation. http://www.yukon-eagle.com/Portals/0/bigjack.pdf


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## ikessky (Sep 2, 2008)

Thanks for the reply.  The Pulse is the high efficiency condensing furnace.  The PVC exhaust is currently run up and out the top of the chimney.  The PVC runs the entire length of the chimney and out of the top.  I'm sure they did this because they removed the old wood stove and were going to seal it up anyway.  I am planning on sending the PVC exhaust through the wall to the outside of the house (like a normal gas furnace would be vented).  The outside air intake for the Pulse is basically a 6-8" plastic tube that looks like dryer vent wrapped in insulation.  It goes from the outside wall, down to the floor and then hooks into the furnace.

The Daka came with a cold air filter box (http://www.dakacorp.com/pdfs/accessories/DAKA 260 DAKA Filter Box Assembly Instructions.pdf).  I suppose I could just make a new outside air intake pipe that is dedicated only to my wood stove.  Can I also tie that same air box into the cold air return for the house though?  So basically it would be that the gas furnace and the wood furnace would have seperate outside air supply, but they would share the same cold air return from the house.


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## ikessky (Sep 2, 2008)

http://img.photobucket.com/albums/v697/ikessky/100_6958.jpg

Here is a picture of the current setup.  As you can see, the outside air intake goes directly into the cold air return from the house.  So my question is, why can't I just take a 6-8" duct and hook it below this one to use the same system as the gas furnace uses?


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## begreen (Sep 3, 2008)

The 8" metal pipe with the sloppy insulation wrap you are showing in the picture looks like a cheap man's cold make up air supply. Leave that alone unless you want to clean up the sloppy work.  

There seems to be a little confusion of terms. The Pulse's outside *combustion* air does not share any connection with the interior cold air return duct. If you look I think you will find that the Pulse furnace also has an exterior air supply pipe (2-3" PVC) supplying combustion air to the furnace. That should be left alone.  Rerouting the PVC exhaust pipe from the furnace to outside is OK, but it needs to be done correctly. All joints need to be properly cemented. Keep the exhaust outlet (on the outside wall) at least a foot from the air intake pipe for the furnace and at least 10 feet away from that fresh air supply (the 8" metal pipe with the sloppy insulation). You don't want fumes from the furnace possibly mixing with that fresh air intake.

The Daka filter box mounts on the Daka. You don't need it if you are going to use the Pulse system's blower for air circulation. If the Daka will run independently, using its own blower, they you probably will want the Daka filter box and will have to run a return air pipe from the side of the Pulse's return plenum to the Daka filter box. 

If you can show a picture from further back that shows both the supply and return plenums it would help figure out the return and supply connections. I would also recommend sketching out a top and side view, simple block diagram of how you propose to connect the stoves and post it here. We can discuss that. Or you could hire a competent sheet metal mechanic. If the wood furnace is in place tying in the supply and return should be about a 2 hr job assuming stock 8" round pipe is used.


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## ikessky (Sep 3, 2008)

http://img.photobucket.com/albums/v697/ikessky/100_6959.jpg
http://img.photobucket.com/albums/v697/ikessky/100_6960.jpg

Yes, I'm getting mixed up with my thoughts and terminology.  You can see the exhaust and intake piping going into the existing chimney.  I guess I didn't know that it was a cold air make-up pipe though.

As far as hooking up the wood furnace to the existing gas furnace, I will be basically doing the exact same thing the Daka manual shows.  The two 8" heat pipes will go from the wood furnace to the upper plenum of the gas furnace.

I basically know what my supply and return lines are for the duct work.  What I'm mainly confused about is tying the existing cold air return into the wood furnace.

Let me know if you would like additional photos or if you still need me to do a block diagram for what I am thinking.  I greatly appreciate the input


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## ikessky (Sep 5, 2008)

Well, I finally took the time to make a block diagram of what I am proposing.  Please note in the diagram that the green  signs are showing the locations of anti-back draft dampers.  Any comments or suggestions would be helpful.


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## ikessky (Sep 5, 2008)

Yes, the gas furnace has a seperate intake and exhaust via the PVC piping you see in one of the pictures.  I may also add another smaller outside air line into the filter box of the wood furnace rather than just rely on the larger one hooked into the cold air return.


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