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plenum re-sizing question

1K views 2 replies 3 participants last post by  ben's plumbing 
#1 ·
I am updating my downflow furnace and air conditioner coil which will sit on top of an original old plenum which is oversize for this new unit. Rather than replace all of the ductwork, I was just going to frame in the new required size with wood, rebuild the subfloor over it and then install the coil and furnace. Now I am questioning my thoughts, is it okay to have bare wood (my framework) inside of the old sheet metal plenum or is this considered to be a fire hazard with the hot furnace above and blowing down through it?
Thank You in advance to all who will share their expertise.:)
 
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