Cut enough aluminum flashing from the roll to wrap around the vent pipe with an extra 6 inches to spare.
Furnace venting into attic.
Fresh combustion air for the furnace is coming from the soffit vents from both roofs.
If you re preparing to upgrade an old furnace it might be time to consider moving it back down to the ground level.
Cut 1 inch deep slots a few inches apart along the top side.
In this video my hvac contractor gilbert rosipal from airrite shows us the inner workings of a 95 efficient gas furnace.
Unless you have a slab where the equipment would likely be in the garage venting can go directly through the roof instead of routing through an exterior wall making it much easier to install the duct work along the upper floor.
You ll see the concentric pipe used.
Attic air is already partly heated from heat in the upper level of your home radiating into the attic despite insulation.
Insulation is only so effective in preventing the heat in the house from going up into the attic.
Now cut 2 inch deep slots.
The furnace has a stack which penetrates the flat roof and is about 3 4 above the roof plane.
Unwrap the flashing from the vent pipe so you can work with it.
Yes in fact this is the most efficient manner of providing air to your furnace.
Bend these newly cut tabs in.
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.