Hot water shortage

afrankofqApril 14, 2013

We have a 2 person Jacuzzi tub which can maintain temperature of the water. The nominal fill is 72 gallons.
We have a 75 gallon LP gas hot water heater that is 5 years old.
When we try to fill the tub, if we run only the hot water, The hot water becomes lukewarm and then cold before we are even 3/4 full.
The hot water tank has been thoroughly flushed. We have a softener so the tank seems to stay very clean.
The initial hot water temperature is about 120 degrees.
The distance to the tub from the hot water heater is about 30 feet and the pipe is insulated.
Is there something wrong with our hot water heater?

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A 75 gallon water heater will not deliver 75 gallons of hot water. It will deliver about 70% of its capacity within 20 degrees of the temperature setting. This means if your tank is set at 125 degrees, you should get about 52 gallons at a temperature between 105 and 125. It sounds like your water heater is functioning properly - it's just undersized to supply your large tub.

    Bookmark   April 14, 2013 at 12:33PM
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Your tub holds 72 gallons of water. If you wish the tub temperature to be 120 degrees, the number of BTU required is approximately 72,058. To have that number of BTU stored in 50 gallons of water would require that 50 gallons to be at about 173 degrees. Your heater may be limited to about 150 degrees maximum. I doubt that you want to be in the tub water at 120, but the figures above offer a comparison. .
The hotter water would be mixed with colder while filling the tub. The hotter water would supply the heat and the colder water would supply some of the required volume.
With what you have now, you could turn your heater to the maximum setting and wait a couple of hours before filling the tub. It might be satisfactory. And the heater can be reset after the tub session.

    Bookmark   April 15, 2013 at 10:03AM
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