adding a water heater

The Tank adding a water heater

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    BTU Bob

    we have a large bath tub- we pretty well drain our 50 gallon gas water heater filling the tub- the gas water heater does not recover fast enough to keep the water in the tub hot. thinking about adding an electric water heater which will serve as a tempering tank (thermostat set low) and using the gas heater for the final temperature rise. the gas heater is in an outside closet and is 15 years old- we have whole house rust and sediment water filters.

    any problems with this idea?

    thank you


    I would put the gas heater first and the electric second, and set both tanks to approx the same temperature. With this setup, the heating should be mostly done by the gas heater (cheaper). Electricity would only be used for the stand-by heating of the electric tank unless you draw more than 50 gallons at a time. I assume that you don’t want a second gas heater because of venting challenges?

    Your plan would help a little bit, but I think that using both at full temperature would give you more bang for your dollar. Another idea would be to increase your thermostat setting if your existing water heater (and mix in more cold water at the tub).

    (I’m an electrical engineer, not a plumber, so my logic could be wrong somewhere 🙂 )

    Larry Weingarten

    Hello: If you know an hour in advance when you plan on taking a bath, you could solve the problem by plumbing an electric heater in line before the gas one and energizing it only when you know you’ll be taking a bath. Alternately, putting a tankless electric heater in line after the gas heater would work also. These units need lots of power supply however.

    If you don’t want to turn the electric heater off between uses, Pigrew’s approach is the right one.

    Whatever, do read up here on replacing anodes. Your gas heater will thank you. Replace the relief valve while you’re at it 😎

    Yours, Larry


    BTU Bob,
    You said gas water heater. Was that natural gas or propane? Natural gas prices almost always beat electricity prices for heating water. But propane is a different story. The therm (100,000 BTUs) of natural gas costs about $1 or slightly less. But the gallon of propane (93,500 BTUs) costs? $3/gallon? Are time of use rates available from your utility? I heat water for $0.0546/kWh.



    A 15 year old water heater?? Could be throwing good money after bad… Maybe a new 80 gallon tank might be a better investment, or two 40 gallon tanks, or a tankless system. I think it would depend how often you fill the tub and how much room you have for water heaters.

    I have a large tub and two 40 gallon gas heaters plumbed in parallel. I have used the tub once in two years(don’t worry, I use my shower daily:D) I only use one heater at a time and alternate every few months. If the urge ever strikes me to use the tub I can simply turn on the other heater and have 80 gallons of hot water.

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