duct work - flex vs rigid

10 years ago

Found a NATE certified AmStd dealer. Came out and gave thorough inspect (# of windows, returns and vents, plus outside shade, infrared inside for insulation, temp of walls, size of existing equip). Was patient and answered all my stupid questions. Waiting for estimate. He mentioned there were 2 small sections in the duct work that were flex - approx 30ft combined. One section is newer, the other is original to house 30+yrs. Rest of the house is rigid and well sized. All was tight, no leaks he could see. This part of the house has more dust than usual. I use the 90 day white pleated filters (FPR 4) but change out every 30 days. Would replacing the flex with rigid be of any benefit not only for dust but also we are upgrading to higher eff AH? Ballpark to replace flex w rigid $600-700. I can afford the extra cost if it warrants.

My old AC and AH units are original to house. I am only replacing this one that has given up the ghost. The AC AH on other side of house keeps the rooms cold, no need to replace at this point. I am considering the AmStd Silver 15 HP 2 ton in either a 15 or 16 SEER and as tigerdunes suggested in a previous thread, going with the GAM5 AH. Will be adding a heat strip.

Featured Answer

tigerdunes

10 years ago

As long as flex is delivering satisfactory conditioned air to the designated areas and is insulated, I would not spend a dime on replacing with hard pipe.

IMO

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Comments (10)

tigerdunes
10 years ago
What do these two lengths of flex serve-ie trunk lines, supply runs, returns? Any idea of the insulation rating on these two pcs? If you don't know, I would ask the dealer. Ductwork is in crawl space? Post back.

IMO
roxan
Original Author
10 years ago
They are not returns, supply lines I think. One runs from the AH to ceiling vent in bathroom, the other to one of the 2 vents in the kitchen which happens to be another ceiling vent. Ductwork is in attic. Have good are flow though, can really feel the air movement. I will ask for specifics when I receive estimate. Have no idea re insulation rating, we bought house 2 yrs ago from original owner, a contractor who built the house for his parents. This side of the house used to be comfortable, hopefully it will be again.
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sktn77a
10 years ago
last modified: 10 years ago
I doubt the supply flex has anything to do with the dust. Generally, hard pipe is superior to Flex but it all depends on the quality of the install. I'd probably upgrade if you intend to stay in the house but make sure the rest of the (old) ductwork is sealed and insulated.
klem1
10 years ago
The dust may or may not be attributed to the flex (I would first suspect return leak between filter and AH) but I would replace it during the upgrade. I'm a huge fan of solid duct but I don't believe I'd spend $700 to retro-fit your existing with solid. If you mentioned this to the contractor I would expect him to test for duct leaks.
roxan
Original Author
10 years ago
He will test for duct leaks and repair, part of the install. I am undecided about replacing the section with the flex. Cost not an issue but I need more info to justify replacement. DH has left this entire decision up to me. I am sure if it were something involving his garage he'd be on top of it in a nanosecond.
klem1
10 years ago
" I need more info to justify replacement."

Your contractor is in the best position to help you justify the replacement. Since cost is of no concurn,just replace the flex with solid and pay more attention to remainder of install.
roxan thanked klem1
energy_rater_la
10 years ago
but...hard pipe has more leakage sites than flex.

make sure they mastic seal (not duct tape or metal tape)

the long seams & joints in ells.

or if air flow is good with flex...just mastic seal

at both ends.

supply boxes should also be mastic sealed to

attic floor.

you can do this supply box sealing from inside the

house by removing supply grill & using hardcast brand

1402 rolled mastic tape. seal the oversized cut at the

bath fans too. use hardcast tape to seal like this:

nothing wrong with flex as long as it is properly sized

& installed.

best of luck
roxan thanked energy_rater_la
energy_rater_la
10 years ago
roxan
Original Author
10 years ago
last modified: 10 years ago
Thanks energy_rater_la and tigerdunes, that helps a lot. The quote includes mastic duct seal at all new connections. If the existing supply grills and bath fans don't already have the rolled mastic I will get some and give DH something to add to his list.