Flow rate.

[MasterPlumbersKeymaster]

With a new natural gas 50 gal GE residential hw heater, what kind of hot-water-only flow rate (in GPM) should I expect to receive? FYI, we have a new 3/4″ line to the house, and all new 3/4″ and 1/2″ copper pipes.

[SylvanLMPParticipant]

To find GPM I would need to know the following.

The pressure available (PSI) and the size of the piping (inside Dia).

Then I cannot only give you the GPM but the FPS not taking into account the friction losses from valves and fittings.

For example if you had a 3″ service pipe with a pressure of 65 PSI your GPM flow would be around 630 GPM and your flow rate would be around 28 FPS

One more point without actually counting every fitting/valve and foot of actual piping we could come close to your actual flow rate but not an exact calculation. Then of course you would have to take the temperature of the incoming water as the temperature effects the weight and then take the height your dealing with as height also takes its toll on available pressure.

For example most hydronic boilers water feeders are set between 12-15 PSI

Knowing that 15 PSI will elevate water to a height of 34.65 ft. Considering the AVERAGE home is less than this height the extra fudge factor in this PSI is to insure a positive pressure to keep this system from becoming air bound. As this water does get hotter it expands thus causing more pressure and here is where the expansion tank comes into play to take up for the increase in pressure (pressure/temperature relationship) ANY way getting back to your inquiry JUST E mail me your pipe size your questioning and your incoming pressure.

[Edited by SylvanLMP on 19 July 2000]

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