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how do you size a water heater

Mellow_2 Member Posts: 204
I have a house with a heating load of 50,000 but a much larger hot water load. The house has two showers and a 30 gallon tub. The master shower has two heads one 4 gpm the other is 2.5 gpm. The second shower is 2.5 gpm. A 50 gallon oil fired water heater will supply 200 gph/ 60 min= 3.3 gpm. This could work for one long shower or two short ones. the custimer wants to take back to back showers and can be in the shower for 45 min. the formulas I have give me the recovery times for tanks and second hour ratings but if the cust. wanted to run the showers without ever running out I would have to look into larger equipment.
P.S. I know the gpm is high and have tryed to reduce it to 2.5 gpm but the cust. did not like the flow.If I add 4+2.5+2.5=9 gpm times60=540 I right in assuming with both showers running I only have 22 min? so the master shower can run for.......6.5 times60=390= 30 min. Is this right and what can be a better way to get the hot water? Oil is the only fuel here now. thanks


  • Radiant Wizard
    Radiant Wizard Member Posts: 159

    What size boiler do you have there? If you decide to use it do you plan on using priority control for the zones? If you use a 60 Gallon Indirect you will get these approx ratings base on boiler but input. This is where priority control comes in.

    Boiler BTU 1st Hour Continuous
    100,000 187 gph 173 gph
    120,000 214 208
    140,000 241 242
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