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We're the second owners of a home built in 2015, and a HVAC technician recently pointed out that our basement furnace piping uses long runs of flex pipe, where hardpipe should have been laid. He said that airflow can become turbulent in these and will be improved with hard piping.

Looking to confirm this information. My residence is a 2200sqft + finished basement with a decent furnace system. Is the air flow in such a residence typically fast enough such that runs of flex piping would disrupt airflow? I have noticed that vents in the first floor that attach to these do feel weaker than the ones in the second floor of my house and thought maybe this was the reason.

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  • At least they stretched the flex tight. That helps flow. The home obviously passed inspection and since it has been 6 years since builder signed off on it I’m sure they won’t be interested in coming back on their dime to change anything.
    – Kris
    Jan 22, 2021 at 15:19
  • Ya they won't - I have some other HVAC work happening now and they offered to fix this at a discounted price over doing it as a separate job later.
    – Adam Hughes
    Jan 22, 2021 at 15:22
  • I would address the leaky looking connections from hard to flex.
    – Kris
    Jan 22, 2021 at 15:27
  • "Is it worth" is very likely opinion based. "Is this flex pipe the cause of x problem" really isn't opinion based. I'd suggest an edit.
    – FreeMan
    Jan 22, 2021 at 15:38
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    Is there a specific problem you are trying to solve? Are some rooms too cool or too hot? Or are you just concerned the ductwork wasn't the "best" available?
    – George Anderson
    Jan 22, 2021 at 16:09

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Flex pipe is the lazy way to put in ducting. I think it should not be allowed for trunk lines and yes you were told correctly it is not as efficient because of the turbulence. I am guessing this was a diy home because of the cobbled sections of round pipe to flex duct in the photo. Unfortunately some use it more than others I only use it for short sections from the trunk to the registers. Installing regular pipe will improve the flow the longer the flex replaced the bigger the improvement in flow you will see.

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  • This was a Ryan Homebuilders house. Do you think this is such a flagrant problem that I should complain? These home builders subcontract stuff out and they cut corners
    – Adam Hughes
    Jan 22, 2021 at 15:07
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    @AdamHughes It's not a "flagrant" problem, just a lazy way of doing it in new/accessible locations. It's used a lot down here in Florida when AC is add to an old home and the ducts are installed in a really tight attic. +1
    – JACK
    Jan 22, 2021 at 15:27
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    It is legal to use so a complaint would not go anywhere. I have found entire homes done in flex, recently a young hvac contractor that did not understand the flow problems and was not sizing the ducts appropriately on a complete home upgrade from baseboards and ceiling heat, to forced air. My friend complained to me and I told him not to pay until the house was finished and balanced. The contractor could not get the air flow so he put in a higher speed fan that blew the trunk lines off at the connections my friend said the contractor wanted more money, in short he got metal trunks at same $
    – Ed Beal
    Jan 22, 2021 at 15:33
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    When I had to replace the duct work at my cabin (it was ALL insulated flex, even the main trunk line), we went with metal for nearly all, but insulated flex for the last 10' or so of a run. The contractor said running hard pipe the entire way can be noisier and some insulated flex absorbs more of the air turbulence noise. And I will say the system moves quite a bit of air and doesn't make much noise. But I'm not an HVAC expert, so take it for what it's worth. If the OP's flex isn't insulated, I'd have to agree with Ed, it's just lazy.
    – George Anderson
    Jan 22, 2021 at 16:04
  • @george Anderson, yes solid hard pipe to the ducts makes more expansion and contraction noise. Using flex from the main trunk to the register makes a quieter system and flex is easier to connect I do admit that but it really should not be used for trunk lines.
    – Ed Beal
    Jan 22, 2021 at 16:31
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It's hard to answer this:

Is it worth replacing this flex pipe with hardpipe?

without knowing what quotes you received or your budget.

Based on a recent estimate I had for HVAC I would guess you're looking at $1,500 to have a professional do it and it should take them 1 day or less. This estimate is based on your pictures only so if there is more work then expect to pay more.

If you do it yourself then expect to pay about $200; this assumes you have the tools already. If not then add $100 for tools and you'll easily sink a weekend or two doing this project.

Will it fix weak air flow? Possibly. Flex pipe is supposed to be sized up compared to hard pipe. So a 6 inch hard pipe is equivalent to an 8 inch flex pipe.

Were corners cut? Yes, clearly. Are they life threatening? No. The house passed inspection because UL listed HVAC materials were used.

It's a done deal, after inspection you agreed to buy the house as-is so it's your problem now.

Welcome to home ownership!

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  • Thanks - the job is going to cost me about $600 if they do it bundled with some other work they're doing, which sounds pretty fair. Ya - I wasn't expecting the homebuilders to do anything about it but I can always leave reviews and my input various places for others to see :)
    – Adam Hughes
    Jan 22, 2021 at 17:22
  • @AdamHughes You're starting to make me think my HVAC quotes were trying to price gouge me, hah. I had 3 quotes from local companies and not just a solo contractor with a truck. Not sure what your situation is. I'm in Upstate NY
    – MonkeyZeus
    Jan 22, 2021 at 17:26
  • for what it's worth, am in Pittsburgh and found this contractor seems more fairly price than others in the area.
    – Adam Hughes
    Jan 22, 2021 at 17:59
  • @AdamHughes Good to know!
    – MonkeyZeus
    Jan 22, 2021 at 18:21

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