Sizing replacement water heater

The Tank Sizing replacement water heater

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    We have a 14 year old 65 gallon gas water heater that is on it’s last legs. I’d like to replace it before it rusts out, but am confused about sizing for our house. We have two bathrooms and a powder room, with a big tub in the master bath. With 65 gallons we have enough hot water to fill the tub, but run out of hot water if a shower is used at the same time.

    This led me to think we would replace the old heater with the same size, but the new models over 50 gallons are significantly more expensive. Can I figure out if a new 50 gallon tank would do the job?

    Larry Weingarten

    Hello: As a rule, you’ll only get from 70 to 75% of the volume of the tank as straight hot water. So for your 50 gallon tank, you’ll get about 37.5 gallons. Depending on temperatures, you’ll vary the amount of cold water needed to mix into the hot to get to the right temperature. For example: if your heater were set to 105, you would use only hot water. If you had cold water temp of 70 and hot water temp of 140, you would use half of each to get to 105, as each is 35 degrees from 105. There is a formula for calculating this, but here is a link to a site that does this for you.
    How many gallons does your tub need? Hope that helps. 😉

    Yours, Larry

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