My Heat pump air handler is in a small closet . One wall of the closet has the filter grill in it, so the closet is under negative pressure as the air handler is open at the bottom and just sucks air from the closet.
The air handler top when the air discharges is connecetd to a big flex duct that goes up into the attic (thru the sheetrock ceiling of the closet).
When I moved in the area around the flex duct was a rough opening bigger than the flex duct- so there was basically a hole around the flex duct into the attic so when the unit ran it sucked hot or cold air from the attic down into the closet- a big energy drain- I have stuffed insulation around it and foamed it.
If I have the unit replaced – its old- what is the professional way to avoid this hole and avoild the “we’l put caulk around it solution- is there one? A pipe with a flange?
Replies
I thought Tim or one of the other gurus of HVAC would have shown up by now, but they haven't, so I'll take a shot.
First go to http://www.buildingscience.com and read Joes ten common mistakes for your area of the country.
It doesn't seem to matter where you live for one common mistake to happen; running HVAC ducts in unconditioned spaces, or worse, putting the whole system in an unconditioned space.
For your current problem, if you can't bring the ducts inside the building envelope, at least go to rigid metal duct. Seal every joint and over insulate the snot out of it. The penetration into the attic can then be tightly sealed around the supply air plenum by reworking the dw and using spray foam.
Your second problem of return air indicates that the opening through the wall is not large enough. It should be sized for the supply produced by the unit. a good HVAC contractor will make that determination and correction for you.
Hope this helps, and maybe one of the others here will add to my limited explanation.
Dave
I've been out of touch for a while, but thanks for noticing!
I agree, ducts in an unconditioned space is less than ideal, and as Edward asked, "What is the professiona way" to address this issue? I would recommend an insulated, sheet metal plenum off of the unit that could easily be sealed at the penetration. Caulk the gap between the sheet metal and the drywall at a minimum, (use of closure angles, like 20 ga bent sheet metal, would even be better) and have the professional check the return for proper sizing.
Tim
Thanks. what is a closure angle?
Best guess here, but a 20 ga. closure angle is a L shaped piece attached to the duct where it penetrates the ceiling. It overlaps the opening helping to seal it off. If the opening is correctly framed for the duct, it also serves as lateral support.
Dave
Exactly. Also important in some installations, though most likely not this one, provides some extra integrity in the event of a fire. IF, sound is an issue, the plenum can be wholly supported by the framing, via the angles, and a flexible connection can be installed between the unit/coil and the supply plenum. Ducts rigidly attached to structures and motrized equipment are notorious noise transmitters.
I think that when you go to replace the unit you may want to look a seperate returns in each room, FL just in the lst year or so put it in the building code that new construction needs to have seperate returns. Installed A/C in '95 and had seperate returns put in each room of out 1906 home, the contractor said that it was a great idea and it has been.