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Thread: Residential condensing or gas high efficiency

  1. #1
    DIY Junior Member 2gomtbike's Avatar
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    Sep 2010
    Bothell WA

    Default Residential condensing or gas high efficiency

    Hello. Looking into replacing my Reliance 50gal gas hot water tank that is 12years old since some other plumbing needs to be done. Just figured out the expansion tank is not working, full of water and that my water pressure is 85 to 100 psi and there is no pressure reduction valve for the house. The tank is in an uninsulated garage with plenty of room around it and vented through roof.

    Was thinking about replacing with a Rheem Imperial Series Energy Star model with 10yr warranty, but just heard about condensing gas hot water tanks and the federal tax credit that ends this year.

    Any suggestion on which way to go or experiences with either? Without the tax credit would only consider the Rheem.

    Thank you.

  2. #2
    In the trades Dana's Avatar
    Join Date
    Jan 2009


    I'm having a hard time getting my head around the notion of replacing a working HW heater that may have another decade of life in it just because you have other plumbing to be done. Unless it's showing other signs of deterioration, purging the sludge off the bottom and replacing the sacraficial anode might be in order, but that's about it.

    But since it's in an unheated uninsulated garage, buy some 3/4" closed cell foam pipe insulation and insulate everything all the hot & cold water plumbing you can get to. Any bare near-tank & HW distribution plumbing is probably half your standby loss in winter. If the local plumbing supply doesn't carry it, buy some online (Grainger sells the stuff as well.) R4-R6 is what you're looking for. The 3/8" wall stuff sold at box-stores is only R2, but even that is worthwhile if you can't/won't get anything better.

    Whether spending more for a condensing heater makes any sense at all depends on how much hot water you use and what your fuel prices are. In 1-3 person households the numbers don't work nearly as well as with 5-8 person housholds. But gas is cheap right now, even if it might not still be cheap in 10 years. If the installed cost delta is on the order of $1000 or more, you may get better return spending that money on a drainwater heat recovery heat exchanger (another plumbing project) than going with condensing vs. standard efficiency HW heaters, if yours is primarily a showering (not tub-bathing) household- especially if they like long or high-flow showers.

  3. #3
    George the Plumber Gsalet's Avatar
    Join Date
    Sep 2010
    San Francisco


    I agree that if you have a small hot water demand a condensing unit may not pay off in the long run, however a tankless may, most tankless have a 20 year life expectancy but requires maintenance at least once a year (couple hundred bucks a year). You really have to do the math, maybe using the tax credit for new windows or insulating the basement would be better money spent. If you do by a new heater make sure you get the heater with the largest R Value (insulation) that extra 10 bucks will pay off the first year.
    Good luck

  4. #4
    Homeowner Thatguy's Avatar
    Join Date
    Aug 2008


    Quote Originally Posted by Gsalet View Post
    that extra 10 bucks will pay off the first year.
    Easily, I think.

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