# Seperate AC and furnace



## Archie79 (Jul 21, 2011)

I'll start by saying that I do very little duct work with my job. So I'm having a probablem designing the duct work for my own house. I have a Harmon wood pellet furnace that I was using as a air handler for my AC. Well after several leaks in the old 10 seer unit I got a entire new system, in which came with a air handler, and I'm horrible at duct design. 

My first question is does it matter if I pipe the supply ductwork into the existing ductwork sideways? ( narrow into wide ) I wasn't sure how that would affect the static pressure.

My second question is do I need to worry about dampers to prevent backflow into the system not being used?
Thanks in advance


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## beenthere (May 30, 2009)

Yes and Yes.


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## Archie79 (Jul 21, 2011)

Yeah that's what I was thinking, but the directions with the furnance said I wouldn't have to bother with either... Normally I would ask a guy at work to design it, but he is on vacation, so I'm stuck doing this one myself... Any hints in general will be appreciated


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## beenthere (May 30, 2009)

You'll either need backflow dampers. or manual dampers to close each off from the other when your not going to use which ever on.

Use splitter tee.


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## airtrackinc (Feb 12, 2014)

1.. as long as your new air handler can deliver design airflow it OK. do you have any sketch that show your existing duct work ?

2.Yes , you need backdraft damper to prevent any shot cycling in the duct.


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