Using flex duct for return.
I am thinking of adding a second return duct to our house, mainly to reduce drafts and even out temperatures. System is a 3 ton heat pump, ecm air handler with 1200cfm max flow.
Our existing and only return is at one end of house and starts from 20x25 ceiling mounted filter/grille and elbow, reducing to 20x14 metal duct about 25ft long and terminates with sweep elbow leading into box at entrance to horizontal air handler. All of this is in unheated attic in Canada.
What seems the best option for the additional return will require a take-off off the existing sweep elbow, a 45 elbow, a straight run of about 12 ft. and a 90 elbow before entering new ceiling filter/grille boot.
Using pre-insulated flexible duct (12 or 14in) would likely be easiest install. Otherwise if metal is used, sealing joints and insulating will have to be done in place in a very tight area.
- Is flex duct suitable for a return duct where pressure could be -0.5"wc ?
- Are there different grades of flex duct? Different materials ? Some of the stuff in box stores doesn't look too good!
- Insulation will need to a minimum of R12. Is flex duct available with R12? If not, would it be practicable to add a second layer or perhaps use uninsulated duct and pre insulate?
If I do this, I will be helped on a weekend by a tinbanger friend who works days on commercial HVAC jobs.
Any help in getting me up to speed would be appreciated!
Flex duct doesn't come in an R12 version, so you will have to wrap it.
Its fine to use for a return.
Did some Googling. Found one type called Quiet Flex that has a pressure rating of negative 0.5" and then Hart & Cooley with negative 0.75" . With almost new filter, we see -0.25", but this should drop with extra return. Seems -0.5" would be OK, but 0.75" better.
Quiet Flex is owned by Goodman and made locally, like Goodman, here in Houston.
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