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90 Degree Fittings For Radiant Heat

I am installing radiant heat under my oak floors on my first story. I will be putting the pex under the subfloor from my heated basement. I plan on doing 2 runs each at approximately 250’ with 1/2 pex.

My question is can I use 90 degree fittings without too much negative impact on the flow. If I’m able to use 90 degree fittings I would be using 6 on each loop. I’m working with some tight spaces because all of the other plumbing and wiring is done and elbows in certain spots to bring the pex into the floor joist bays would allow me to put the pex in the places I want. 


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,838
    A 90° fitting has an equivalent length of 5 feet to 30 feet depending on how tight the turn is inside the fitting. This needs to be applied to the pump head required to move the water thru the loop. It does not add any significant length to the heating capacity of the loop.

    This means that you may need to get a circulator pump with a greater capacity. But I would give it a try with the existing pump (or the pump you have chosen) to see if it works. It probably will. But if it does not, just get a more powerful pump.

    Or you can do the math by getting the equivalent length of the 90° fittings in excess of the normal number of fittings. Then do the calculation based on that new "longest run"

    If you don't know how to calculate pump head requirements, there are several resources available herein.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • cjohnsen
    cjohnsen Member Posts: 3
    Thank you for your comment, that gives me some good info.

    Just for more info, the current pump that is installed is a Grundfos UPS15-58FRC and i will be using Uponor ProPEX 90 elbows.
  • Tinman
    Tinman Member Posts: 2,808
    3/8" tubing is much easier to work with in those types of application. Maybe three loops around 170' each?
    Steve Minnich
  • HomerJSmith
    HomerJSmith Member Posts: 2,441
    edited November 2020
    Pex A can be bent 180 deg if you maintain the published radius.

    I have used a heat gun to loosen the plastic which makes the bends easier without kinking. Slow forming the bend would minimize kinking, too.

    If you do use 90's, I would keep my loops short. You don't want to go to the published data for 1/2" pex of 300'. Also, some 90's have an ID smaller than the pex and are a sharp 90 which would increase pumping demand.
  • TAG
    TAG Member Posts: 755
    They make metal holders for 1/2 pex that will bend the pipe in a fairly tight 90 -- nothing like a fitting ... but tight enough that I used them in walls for my panel radiators. Also along rafters --then the 90 bend into the wall
  • heathead
    heathead Member Posts: 234
    Does someone make a 180 deg plastic holder to bend the pipe in? Like the 90 deg plastic ones. Or does someone?