I think a cmp cable cost twice a non rated cable so my guess is all your communication fire alarm and misc.
Attic furnace no return plenum.
Anyhow the return box and the other box that has the ducts coming out of it are made of sheet metal.
If the space is conditioned it no longer is an attic and needs to be called conditioned space wiring within an area used as a plenum has to be in conduit.
Tesp is typically measured using a manometer and a dwyer 303 static pressure tip inserted into the return plenum just before the filter and in the supply hopefully before the coil then add the two numbers disregarding signs.
My mother has had me going up into her attic to seal the leaky ducts and parts of the plenum air handler that join up to the furnace and coil units.
Inspectors can learn how air leakage from ductwork may cause home energy loss increase utility bills lower comfort levels and make the hvac system less efficient.
I used to work in house at a 40 story high rise.
I have a huge concern about fire safety.
The rating plate will state the max.
The return is on top and the supply is on the bottom.
No return air plenum.
Ceiling space as a return air plenum.
If you have a door at the top or bottom of the stairs you can replace with a louvered door.
An attic is a space not a structural component the space cannot support anything but air.
The return air plenum was a room with doors and banks of filters.
No radios or storage.
If there is no return duct the concept is that the attic space becomes a return air plenum and this is not uncommon in commercial plenums.
The sealed attic is great with return and supply duct inside of the thermal envelope of the building.
Otherwise this is a code violation.
As noted by one previous poster all materials in the attic must be plenum rated.
A 14 trunk too small emerges from the foundation wall in the basement in a roughly 2 2 notch at the top of the foundation wall.
Everything would need to be plenum rated including the low voltage cabling.
As long as there s an unobstructed path e g no door that can be closed the upstairs doesn t need a dedicated return.
Static pressure but it is usually 0 5 wci.
When i was removing the trunk i found that they simply used a 14 elbow under the furnace not a proper plenum box.
Cabling is not rated for plenum use.
Building cavities used as return air plenums is one of the leading causes of duct leakage in homes today.
Not to mention that the air handler itself is in its own plenum.
How can and attic be held to the same standard as a plenum when its used for storage and water heaters and such.
