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Measuring flow rate to determine circulating pump for radiant floor heating

tooz Member Posts: 1
I'm new to the forum so please excuse me if I'm in the wrong category. I'm installing a radiant floor heating system, am a DIY er and am trying to determine or get a recommendation for the right size circulating pump. My system contains five loops of 1/2 pex of approximately 250 feet each. Three thermostats control the five loops - three loops will be run by the same thermostat while each of the other two loops are controlled by their own thermostat. There are no elbows in any loop - the loops attach to a rehau manifold with rehau actuators. My system is heated by my 75 gal domestic hot water heater which has ports for radiant heat. The entire system is at floor level. The distance from the heat source to the manifold is approx. 15 feet and will have approximately 8 elbows in the one inch pipe between the heat source and manifold. I don't know the flow rate (and don't know how to calculate it) which is the main reason that a pump manufacturer like Gundfos can not make a recommendation. Any help would be much appreciated - thank you!


  • Rich_49
    Rich_49 Member Posts: 2,579
    We really need to know each individual rooms BTUh requirements to provide the help you requested . Was a heat loss ever done ? How did you determine what was needed for spacing and water temps ?

    If it's only 3 rooms I will run the numbers for you . I need room dimensions and ceiling height , insulation values below the floor and in the ceiling , whether the space above is heated or not , same as with space below the rooms to be radiantly heated , Exposed wall lengths and heights , size and type of windows and doors on those exposed walls , R values for the walls , what type finish floor coverings in each room and finally where you are located along with your desired indoor temp at design . That's alot to not have figured out before your install , we'll get you fixed up if we can .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • Ironman
    Ironman Member Posts: 6,400
    A very generous off from Rich. We normally charge for design services.

    Another question: is this in a slab or in joist?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.