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Fancoil pressure drop

BC_3 Member Posts: 12
Maybe the flow meter itself has a significant pressure drop? the pressure drp through some meters is huge as they approach max flow. They should have data on this. Maybe the spring check, although I wouldn't think that would contribute much.


  • Tom Hopkins
    Tom Hopkins Member Posts: 552
    Pressure drop -- fancoil system

    I have an ESP HE-50 hot water fancoil connected to a standard 75 gallon direct vent tank type water heater.

    The mfgr calls for 5GPM through the fancoil which is 1/2" copper. Literature states that there is 5ft/hd drop through the fancoil. The rest of the piping is about 20' of 3/4" copper to and from the tank. 1 spring check. With a Grundfos 15-42 pump on high I am getting only 2.5GPM through the loop!

    The pump curve of this unit tells me that at 2.5GPM I have about 16 ft/hd. Where is all this resistance coming from?

    The two items I have considered are:

    1) Because of space considerations I do not have 5 straight inches before and after the pump. The pump is just after a 90° elbow out of the fancoil. Does it matter that much?

    2) I have returned the fancoil to the cold water inlet (dip tube) of the water heater. Is there that much resistance through the tank? Would it matter if I returned it to the drain fitting at the bottom of the tank where the hot water re-circ is located?

    I'm pleased I put a flowmeter on the system to see what is really going on, but am suprised that I would need so much pump to get my flow rate.

    Who's got insight on this one?


  • tim smith
    tim smith Member Posts: 2,738
    flow rate

    I wonder if your flow meter is right. Was is the delta T of air side. What about checking your actual pressure drop across fan coil. either one of these can tell you what actual flow rate is. Tim
  • Tom Hopkins
    Tom Hopkins Member Posts: 552
    Flow Meter

    The flow meter itself is very accurate. A blue white graduated cylinder type. However it IS installed right after the pump where there may not be good laminar flow.

    I do not have the ductwork connected yet so I do not have the delta T of the water in and out.
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