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Flex duct under house?
Ok. The house we are looking at did not have central heat/air. The owner installed a 2 ton heil package unit (the house is 1200 sq ft with 8 ft ceilings). The duct work under the house is all flex duct. The plenum is a 24 inch flex duct with 4 runs coming off of it that are all about 25 ft long and are also flex duct. The plenum is laying on the ground and the runs are held to the joist every 4 ft or so by a fabric strap. In between the straps there is about 5-6 inches of sag in the flex duct. In your professional opinion, is this acceptable procedure?
Only people who are knowledgable in hvac please.
Thank you very much!
3 Answers
- 8 years agoFavorite Answer
As long as the layout is balanced..it sounds as though you mig ht have a underlying concern about capacity overall?...As long as the ducts are not on the ground;that's always a plus;there are codes regarding ducting ;they vary state to state;they are geared towards water (having adequate heigth etc.
depending on what part of the u.s. your in.Florida for instance has strict codes on new construction/but package units are used mostly on mobile and manufactured homes here...I would have a hvac company come out and do a good inspection;let them know up front what your concerns are.As long as the system isn't leaking air;is adequate in return size ...the 25 foot supply runs are going to have to be real small in order to maintain static pressure(I don't think friction loss from the (sag")is your problem...with a two ton unit and 4 -25? Foot runs...I don't see where air volume is going to be adequate .....consult a tech.have them bring a magna-helic...(measure your cfm(etc....
Source(s): Ac tech - ChuckLv 48 years ago
Yes, flex duct strapped every 4 ' is pretty much Code compliant, although we would prefer to see no more than 4" slack (1" per ft.). It is true that the slack adds 2'-3' to a 25' run, but that shouldn't be a big problem if everything else is sized properly. My main concern is that the system may be a bit small. Also, check and make sure you have as much return air as you do supply air as you can't blow out what you don't pull in.
Source(s): HVAC TECH - daffyduct2006Lv 68 years ago
No it's not correct. However there is no real code as to it's length. Manufacturer recommendations is to be no longer than 25 ft. I do HVAC for a living and I feel (as do most architects and engineers that draw up the blueprints for commercial installation) that the flex be limited to 14 ft. The ideal installation to use only a short piece to connect the round metal pipe to the registers if need be. This normally occurs with drop in registers in a drop in ceiling. There should be no sags either. Although there is no code against it, I personally would not use it at all in a crawlspace.
