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Thread: Two water heaters

  1. #1
    Retired tool & Die and Mechanic Giles's Avatar
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    Default Two water heaters

    I recently moved into a different home and the previous owner installed a gas water heater along with the original electric one. He said he did this because he was charged a minimum each month for gas and wasn't using any.
    The heaters are feeding the same water line and they are about 50 foot apart.
    I have plenty of hot water but was wondering if this is overkill for two people.
    Should anything be changed? Both heaters are about 7 years old.

  2. #2
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by Giles View Post
    was wondering if this is overkill for two people.
    Normal usage is a 100 gal per person per day, with a maximum of 2/3rds of this water being hot.

  3. #3
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by Thatguy View Post
    Normal usage is a 100 gal per person per day, with a maximum of 2/3rds of this water being hot.
    No, that's not even close to right with respect to hot water use. At that rate a family of 4 would use about 750 ccf/month of gas. That's about three times the Energy Guide rating. Even half that much would probably be toward the high side. Non-hot water uses such as toilets make up a big fraction. The actual hot water use is mixed anyway except for the dishwasher. Shower fraction might be 2/3 hot. Warm wash is ~1/2 hot, but only on the wash cycle, not the rinse.

    I'm not even sure that it is correct for total water use, but I have seen the 100 gal/day per person figure quoted, but don't put much stock in it. My family used to use about 50 gallons/day per person, but are now in the 25 gal/day per person range with about 11 gal/day per person of that being hot water as best I can tell.

    Judging by the following: http://www1.eere.energy.gov/building...cycle_1098.pdf The U.S. average was around 19 gal/day of hotwater per person in 1998.

  4. #4
    Homeowner Thatguy's Avatar
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    35 input therms/month for our NGWH for two people.

    Let's say 21 therms actually go into the water, incoming at 50F and heated to 120F.

    This is 21E5/(120-50) = 3E4 pounds of water = 3600 gals/mon = 120 gals/day = 60 gals per person per day of hot water.

    Our WaCo says we use 255 gals per day (we're irrigating our new lawn) = 127 per person per day.

    ?
    I guess it's in the ballpark, or in the town that the ballpark is in.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default heaters

    HOW the heaters are connected to the system. and their sizes, is more important than how far apart they are. In most cases one gas heater, if it is the proper size, is more than adequate, and cheaper to operate than an electric one.

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