What size hot water tank for a 50 gallon whirlpool tub?

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David Criss

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Corydon IN
I've a customer that wants a whirlpool tub. She has a 50 gallon electric hot water tank and no room for a 2nd tank. I'm thinking that most of these whirlpool tubs are in the 45 to 50 gallon capacity and the general rule of thumb is a hot water tank only delivers 60% of it's capacity in hot water so it'll only produce 30 gallons of hot water before it starts cooling off. Is that correct? What size hot water tanks do people use to supply a 50 gallon whirlpool tub?

Or, do the whirlpool tubs also work as hot water heaters and can bring water temperatures up with an internal heating coil? Thanks, David


Retired Defense Industry Engineer xxx
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New England
Some tubs do have inline heaters, but they are mostly designed to maintain the temperature, not raise it, and only work while the jets are on as they are inline with the pump motor.

That tank might work if the storage temperature was raised, and a tempering valve added. It wouldn't if there were other hot water uses needed either before, during, or near-term after filling the tub. You can usually get a bit more than 60% of the tank out. A thermostatically controlled fill valve would let you maximize the amount before the outlet temp varied...it should be able to hold the temp until the tank's temp dropped to nearly your set temperature. Many thermostatically controlled valves also tend to have slightly higher gpm flows, filling the tub faster, but also giving the burner less time to help increase the amount of hot water (not that big a factor when filling a tub at maximum flow, though).
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