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Thread: Replacing the current gas heater with a smaller heater

  1. #1
    DIY Member paulsiu's Avatar
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    Default Replacing the current gas heater with a smaller heater

    Hi,

    One of my relatives' water heater is leaking from the bottom. It appears that the bottom is corroded and probably needs to be replaced with a new one. They currently have a Richmond 7K50 50 gallon gas, 40,000 BTU. First hour is 74 gallon.

    They used to have several kids around the house, but they have all grown and left the house. The question is can they save some money and install a smaller unit. There is a GE Model GG40T06AVG01 at Home Depot that has a 40 gallon tank, 36,000 BTU, but the first hour is only 67 gallon. Do you think this is enough for 2 people and may be 3 (when someone visits). Will there be a problem with hooking up compatibility?

    The dad will apparently hook up the heater. He has apparently done the last two.

    Paul
    Last edited by paulsiu; 06-18-2009 at 09:12 AM. Reason: wrong title

  2. #2
    Homeowner Thatguy's Avatar
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    Normal usage per person per day is 70 gal, some of which I guess is cold water.

  3. #3
    Geologist sjsmithjr's Avatar
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    Default Sizing Calculator

    You may find this calculator handy:

    Water Heater Sizing
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    I was told some places determine the size of the WH based on the number of available bathrooms and fixtures; not how many are actually living there. So what's practical for you now might not meet code or the next occupants.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    DIY Member paulsiu's Avatar
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    Default

    I looked at various sites and gotten different ways of sizing a tank. Most of them follow a principal of calculating a maximum load from water usage.

    The relatives indicated their existing tank isn't very good. if they take 2 showers, the water upstairs takes a hit. Since the tank is 74 gallon first hour, how can that happen?

    Paul

  6. #6
    Plumbing Designer FloridaOrange's Avatar
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    Quote Originally Posted by paulsiu View Post
    .. 74 gallon first hour, how can that happen?
    If the unit is old and not well maintained it's not as efficient as it once was.
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    Another issue is the spec is based on the incoming water being a certain temp...if yours is colder, it won't produce as much hot water. One way to extend the capacity of the WH is to run it hotter, then mix the output with cold as required to keep it safe for people. This is done with a tempering valve at the output of the WH. This gives the effect of having a larger WH. It also can be safer since it is generally considered that 140-degree water is required to kill various nasty things that MIGHT be in the tank. Normally, this is only a problem when it sits, but 120-degree water (a common setting) is nearly ideal incubator temp for nasties.

    Last edited by Terry; 08-06-2011 at 01:23 PM.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    Homeowner Thatguy's Avatar
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    74 gals = ~610#
    40F to 140F takes 18 kwh
    70F to 140F takes 13 kwh.

  9. #9
    In the trades Dana's Avatar
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    If they have a hydronic (forced hot water) heating system with a reasonably new (less than 15 years old) boiler they should forget about a standalone HW tank and spring for an indirect-fired tank running off the boiler. It'll outlast the boiler, run at comparable or better efficiency as the standalone during the summer, and at signficantly higher efficiency during the heating season (improving the as-used AFUE efficiency of the boiler at the same time.)

    There is federal tax credit subisdy for this, and in many areas other incentives may apply as well.

    It's really the right way to go- more efficient, one burner to meet the two largest thermal loads, one appliance to maintain, etc, etc.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default heater

    In most cases the difference in price between a 40 and 50 gallon heater is negligible. There are no compatibility issues with either heater.

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