Air circulation fan

[mathew stouffer]

This air handler was in an insulated attic of a town home built in 05. There were two units, although this was the only one I could access. Does the air handler need to be connected to the vent via duct work or will installation of a filter over the front of the air handler do.

[David Bell]

Ducted ,sealed, insulated, firestopped. That space is obviously not plenum rated.

[Jerry Peck]

Looks like they are using that as a return air plenum, and there are a lot of things in there you do not want in a return air plenum = so installing a duct to connect the air handler to the return air grille looks to be the wise thing to do.

From the insulation, I am having a problem understanding where the condition space thermal envelope is in that photo.

[mathew stouffer]

Jerry,
It is a vaulted ceiling with foam insulation on the ceiling and walls, so the entire area is within the thermal envelope.

[Jerry Shipman]

From NFGC that most manufacturers base thier installation manuals upon:

Where a furnace is installed so supply ducts carry air circulated by the furnace to areas outside the space containing the furnace, the return air shall also be handled by a duct(s) sealed to the furnace casing and terminating outside the space containing the furnace

[Rod Butler]

That does not appear to be a furnace and the ceiling and walls are not fire rated. As long as the thermal envelope is protected above I see no violations. A filter on the fan would be a good idea.

[ray jackson]

Rod, I believe you are correct about the thermal envelope. However, just because that space is within the envelope doesn't mean it can be the plenum. That insulation shown in the picture alone isn't allowed to be in the air stream. Then all the electrical and anything else in the space must be plenum rated.

[Darrell Udelhoven]

It is important to know what the purpose of the fan is.
Does it circulate air into the living space?
If it does, it cannot be left unconnected to the return air grille.

If that is an air conditioning air handler with an evaporator coil, then pulling Return-Air from that area would defeat the very purpose of a Return-Air system. In cooling mode, there are also major temperature differences between conditioned living area, - defeating the effectiveness of the A/C.

"The Return-Air must equal the Supply-Air to & from the living area."
It would be drawing a lot of air from outside of the living areas.
That is certainly NOT a living area, & among many other things, would defeat the purpose of a Living-Area Return-Air system.

I don't know why anyone would do something like that!
What is on the other side of the Return-Air grille, - living areas?

I am a retired long time, back to the mid-1970's HVAC contractor & Tech; the contractor should have pulled a city permit, IMO an the HVAC city inspector should have written that mess up in a NY minute. - Darrell

[Jerry Peck]

Jerry,
It is a vaulted ceiling with foam insulation on the ceiling and walls, so the entire area is within the thermal envelope.


Then it is a return air plenum and I see all kinds of things one does not want in a return air plenum, not the least of which is the fiberglass insulation, plumbing DWV piping, NM cables, exhaust fans, etc.

[mathew stouffer]

From what I could gather, the fan is pulling air out of the living space and attic and exhausting it to an exterior location. I was unable to locate supply vents in the home.

[ray jackson]

From the looks of that blower they are exhausting a huge amount of air. Is that some version of a whole house fan?