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Thread: Water heater sizing help

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  1. #1
    DIY Senior Member DavidTu's Avatar
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    Default Water heater sizing help

    3500 sqft house with finished basement (1 bath), main floor with kitchen (2 sinks) and powder, 2nd floor with 2 baths including master shower w/ 2 heads and separate tub.

    How big of a Tank water heater do I need? Model recommendations welcome. Or better to have 2 water heaters? main trunk is 1" how do I connect to tank? (ie can I get tank with 1" fittings?)

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    The further away the WH is from the point of use, the larger the pipe run, whether there's any insulation on the piping, and whether it runs through unheated space all help to determine how long it takes to get hot water to the point of use...it could be quite a long time. You may be a candidate for a recirculation system.

    Then, you want to determine how many hot water users are likely to be running at once, and for how long. Use the manufactuer's specs for flow. If you like long, hot showers, and others may be doing this while you are, that would change things. If you have a large soaking tub, that would change things. Do you do clothes in warm or hot water at times? So, it's not one size fits all. You also didn't indicate whether you wanted either an electric or gas fired water heater.

    Then, if gas, what size flue? Would you be willing to vent out the side of the house, or must it go through the roof? Do you have room to put a WH on say each end of the house so one would be closer to the points of use? All of these things affect what kind, size, recovery rate, and applicability to your situation...no one size fits all. Then, it seems some codes have guidelines on what they expect, possibly based on the number of bathrooms.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Homeowner
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    How many bedrooms? How many big tubs?

    If your main trunk line is 1" you better install a circ system or split the system up......it would take forever to purge the cold with a lav faucet.
    Last edited by Hackney plumbing; 02-03-2012 at 02:39 PM.

  4. #4
    DIY Senior Member Runs with bison's Avatar
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    Natural gas? Electric? LPG?

    From what I've seen the limiting case is filling a big tub. A 50 gallon natural gas fired tank can fill a whirlpool tub to a very warm temp if the water heater temp is in the 130+ range (but comes up short at 120-125...speaking from experience.) However that will essentially empty the tank and then there is recovery time. Recovery time for electric is slow. For my 2800 square foot, 3 bath/shower home with 2 kids, 2 adults the only time we have run out of hot water with a 50 gallon tank is filling the tub. This was true even when all three showers were being used and we were using standard 2.5 gpm showerheads--although we are not long showerers. We now use 1.5-1.6 gpm showerheads.

    Assuming you have the physical space for it I would opt for a 70-80 gallon tank. The standby losses don't change much with a larger tank and it should suit all your needs. Not sure if you can get that with 2 inches of insulation foam for the tank, but that is what I would look for.

    If things aren't already enclosed, I suggest insulating all of the hot water lines all the way to the fixtures, particularly with the 1" main header. This will make the cool off time between draws much longer--very helpful on long runs to kitchen faucets and such. I also insulate my hot water line out of the tank--but with natural draft on a gas system you have to use non-flammable/non-melting insulation in the first foot or so adjacent to the exhaust vent. I also do pipe insulation on the T&P valve line and valve body (brass and copper projections like this waste a lot of heat because they have high conductance and a lot of surface area.)

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    Homeowner
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    Split the system up and use 3/4" pipe.........and two water heaters.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Two water heaters will have more 'input" than a single one with the same total capacity, and probably cost less than the single heater. I would connect them in series, others would use parallel, but it is an individual preference.
    Licensed residential and commercial plumber

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