A case of incompatibility.
Builder sprayed insulation all over furnace in attic.
A furnace in the attic is a design that works for all homes.
But then the questioner mentioned that the spray foam contractor had intentionally left big holes to the outside by not sealing the gable vents.
In a proper spray foam job a contractor doesn t just spray foam all over the top of your attic and go home.
You might not receive the same air movement benefits if the unit is in a garage either.
Most often the attic is sealed by installing spray foam insulation at the roofline thus bringing the attic inside the building enclosure and turning it into conditioned space directly or indirectly.
If you don t have a crawl space or a basement then it can be a challenge to place a furnace on the ground floor of the structure.
A while back i wrote about the incompatibility of putting an atmospheric combustion furnace in a sealed attic.
You can build a small enclosure around the furnace with rigid foam insulation then pick up the insulation on the ceiling inside the enclosure.
If you pipe the air in directly to the furnace and it does not use attic space air then you can use sprayfoam.
A plenum is the source of combustion air.
If the air is not piped in directly to the furnace the attic space would be considered the plenum.
Any existing batt or roll insulation in the attic should have the facing against the attic drywall floor or no facing at all.
Insulation should be rolled out perpendicular to the joists and unfaced rolls should be used.
If this house has a basement then both handlers or furnaces should be installed there.
The attic floor needs an insulation value of r30 40.
If the furnace is a fuel burning one be sure you provide air for combustion.
The attic is the worst place to install hvac equipment and duct work.
This puts the furnace in at least semi conditioned space.
The rigid insulation was saturated from condensation.
I found instead a vintage 3 ton ac unit with 1 rigid insulation taped all over it and insulated flex duct snaking all over the poorly insulated attic.
She asked me to go into the attic to find the roof leaks or where the snow is blowing in through the soffits.
Otherwise humidity will quickly creep into your attic.
Batt or rolled insulation or blown loose fill insulation fiberglass or cellulose can be installed on top of old insulation.
Gable vents and soffits are the big culprits here.
