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I need to replace a 75-gallon water heater. What are the options?

r-m-w | Posted in General Questions on

Gas versus electric or tankless.

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  1. iLikeDirt | | #1

    Do you already have gas? How many people are in your household? What are your electricity and gas rates? Is space at a premium in your utility room or where the old unit was located?

  2. Tim C | | #2

    And what are your hot water requirements? Huge garden tub? 2 hour long showers?

  3. r-m-w | | #3

    Space not an issue. No excess water needs. We have a recirculating system as water heater is below house.

  4. davidmeiland | | #4

    I'd go with a 50 gallon tank. Choice of gas vs. electric would depend on rates you pay and which you have easily available at the water heater location.

  5. GBA Editor
    Martin Holladay | | #5

    Here is a link to an article that provides guidance for homeowners making a decision like yours: The Water Heater Payoff.

    The article includes a decision tree (reproduced below).


  6. user-2890856 | | #6

    What type of heating system and water heater do you currently have ? How many adults and children also should be asked and are thsoe children if there are very active , ages .
    I would suggest a 40-50 gallon , very well insulated NG storage water heater . Have your plumber arrange to store at 140*+ and mix down to 115-120* . By doing this you will accomplish 2 things .

    1. Kill bacteria which colonize in water heaters such as Legionella . It really is a concern that should be factored in .
    2. This strategy will increase the storage capacity , not in gallons but in energy . You can get a better result from a 50 set up this way than a 75 set up to store at say 120* .

  7. Dana1 | | #7

    If you're heating the house with a hydronic boiler, an indirect-fired tank running as a zone off the boiler increases the duty-cycle on the boiler (which improves it's as-used efficiency), and provides faster recovery than most standalone HW heaters. Indirect HW heaters also have much lower standby loss than standalone tanks, since there is no center-tank heat exchanger flue convecting heat out of the tank 24/365, and have fewer gaps in the insulation.

    Tank HW heaters (almost) never need to be bigger than the biggest tub you need to fill. If you have a high-volume soaker-tub there may be a reason for the 75 gallon tank, but otherwise there's no good rationale. With indirect tanks on bigger boiler (100,000 BTU/hr +) you can usually even down-size the tank to 30 gallons and still fill most tubs, since it make hot water at a sufficiently high rate that the temp at the tap won't drop below bathing temp. (If it does, bump up the storage temp by another 10F.)

    With recirculation systems HW heating efficiency can be undercut significantly if it is keeping the distribution pipes hot even when hot water isn't going to be drawn. The type of control matters- demand types are far more efficient.

    If the distribution plumbing under the house is uninsulated but accessible, it's well worth retrofitting R4 (3/4" wall closed cell foam) pipe insulation over any and all you can get to- even the "return" line. This will reduce the duty cycle requirements of the recirculation pump by keeping the water warm enough to be useful for extended periods between draws, and it will reduce the overall thermal loss of the system. Insulating the cold water feed to a hot water tank for the 6-10' nearest the tank as well as any temperature/pressure overflow plumbing nearest the tank also reduces standby loss. (With gas-fired heaters be sure to leave sufficient clearances between the flue or burner and the pipe insulation to meet fire codes.) The 3/8" foam pipe insulation sold at box stores only about R2- better than nothing, but nowhere near the maximum financially rational R value. (Code minimum insulation for tempered water distribution under IRC 2012 is R3.) You may have to go online to find it, but it's out there. The pre-split stuff is easiest to deal with in retrofit situations.

  8. wjrobinson | | #8

    Reality; Heat lost from hot water recirc where I live heats the home. So the heat is not lost for much of the year.

    Neat trick to bring hot water to a far bathroom, plumb the toilet with hot water, use toilet, flush, waa laa, less cold water to dump at the sink next or shower and you have used the water instead of wasting it.

    Kills two birds with one stone too... no more sweating toilets ruining subfloors bringing in carpenter ants for me to remove. (lost job for me which I have performed more than once)

    Can't patent that idea, wish I could.

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