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HVAC return

Daniel Powell | Posted in General Questions on

I’m building a new house in East Texas, hot and humid, with a conditioned attic space. My Hvac unit is sitting within a few feet of my attic access door. The Hvac contractor wants me to just install a louvered door to the attic instead of running a dedicated return register for the Hvac unit and dehumidifier. I was ok with this at first but now after thinking more about it I’m concerned about this pulling the entire attic space into more negative pressure this way promoting air infiltration from the exterior. Any thoughts on other possible downside to not running a dedicated return register to nearest wall and just using a louvered door? Thanks

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Replies

  1. Cramer Silkworth | | #1

    As long as the louvered attic door has enough free area and low enough pressure drop (so it can easily pull the return air through) there should be minimal if any depressurization of the attic space. Your HVAC contractor should be able to easily test this with a manometer with the access door open and closed to see if the pressures change much (<3 Pa ideally). As long as the attic space is properly sealed and insulated there's not really any difference between that and a return ducted to the main living space. There may be a slight energy hit depending on the loads coming from the attic itself (minimal if it's really well sealed and insulated), but I think there's some benefit to pulling that return air through the attic to keep it truly part of the conditioned air volume and not get stagnant/stale/etc. Once more for good measure: ONLY IF THE ATTIC IS ACTUALLY WELL SEALED AND INSULATED. Your mileage may vary, this bag is not a toy, consult a doctor if condition persists, etc...

  2. Expert Member
    Akos | | #2

    A proper return in this case is two fittings and grill plus maybe one hour extra work. Why skimp on it?

    Even if your attic is well sealed, depressurizing it brings humid outside air in, so it is something that can only cost you operating cost down the road for minimal install cost savings.

  3. Daniel Powell | | #3

    Thank y’all for the replies. The return register was included in initial bid but after seeing that it would go right next to the attic door and the idea of a louvered door came up I kind of got the feeling my Hvac guy wanted to save himself some money. Hvac contractor said he had a problem with condensation in another house and that Is how they fixed it with pulling return through the conditioned attic space, not that that should matter for my house. I don’t mind the louvered door as long as the system will still function the same. But then I have to pay for a custom louvered door as it is an odd size so a dedicated register would really be better for me. Just want the Hvac system to function the best way possible.

  4. Jon R | | #4

    If it's reasonably large, you are talking about small fractions of a pascal - not something to worry about.

  5. Walter Ahlgrim | | #5

    I am not sure I like the idea of the only return being a single 14 x 20 inch attic hatch seems too small for most housed, even if it were 22x22 that seems a little small but close. But 3 grates about that size scatter around the house does sound appleing.

    It is important to move enough air thru the attic so it stays close to the same temp as the house. You will need some supply and return in the attic with adjustable grate so you can tune the system.

    Walta

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