If you re preparing to upgrade an old furnace it might be time to consider moving it back down to the ground level.
Furnace venting into attic.
The reason for this advantage is the fact that venting for your furnace requires less work in an attic than it does in other locations of your home.
Now cut 2 inch deep slots.
Yes in fact this is the most efficient manner of providing air to your furnace.
Cut 1 inch deep slots a few inches apart along the top side.
Bend these newly cut tabs in.
Fresh combustion air for the furnace is coming from the soffit vents from both roofs.
Cut enough aluminum flashing from the roll to wrap around the vent pipe with an extra 6 inches to spare.
The furnace has a stack which penetrates the flat roof and is about 3 4 above the roof plane.
You ll see the concentric pipe used.
In this video my hvac contractor gilbert rosipal from airrite shows us the inner workings of a 95 efficient gas furnace.
However the furnace is in an attic space which has no venting for warm humid air from house from soffits from hot roof etc to escape.
Insulation is only so effective in preventing the heat in the house from going up into the attic.
Attic air is already partly heated from heat in the upper level of your home radiating into the attic despite insulation.
Unwrap the flashing from the vent pipe so you can work with it.