That is because with an attic installation vents must go down into the thermal envelope to deliver warm air.
Furnace venting into attic.
Attic air is already partly heated from heat in the upper level of your home radiating into the attic despite insulation.
Bend these newly cut tabs in.
Fresh combustion air for the furnace is coming from the soffit vents from both roofs.
The furnace has a stack which penetrates the flat roof and is about 3 4 above the roof plane.
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.
In this video my hvac contractor gilbert rosipal from airrite shows us the inner workings of a 95 efficient gas furnace.
Yes in fact this is the most efficient manner of providing air to your furnace.
If you re preparing to upgrade an old furnace it might be time to consider moving it back down to the ground level.
Insulation is only so effective in preventing the heat in the house from going up into the attic.
Now cut 2 inch deep slots.
Unwrap the flashing from the vent pipe so you can work with it.
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.
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.