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Thread: Tankless?

  1. #1

    Default Tankless?

    I have an A.O. Smith 50 gal, I assuming it's an 80s model and a Utica gas-fired boiler, again, possibly from the 80s. I have a 4BR, 2B 2200 sq. ft. home in NY and was thinking of switching to a tankless wh as part of the NYSERDA Energy Star Program. Doing so, in addition to other measures I've taken, would qualify me for 25% cash back on the entire workscope.

    My question is, given where I live, would a tankless deliver adequate pressure and temperature for 2 simultaneous showers? From what I've read, the tankless units drop the pressure when under more than one load. I'm a big fan of high pressure and don't want a trickle of hot water coming at me if someone else is showering at the same time. I don't have any multi-sprayer showers, just one tub/shower and one standalone shower with a showerhead and handshower...they cannot be run at the same time.

    Does it make sense to go tankless, or should I replace the old boiler and wh and get a boiler-fired solution. From what I've read, those seem to be the next best as far as energy efficiency.

    Please advise. Any info is great appreciated.


  2. #2
    Plumbing Designer FloridaOrange's Avatar
    Join Date
    Dec 2005
    SW Florida


    I've designed plenty of systems using tankless water heaters. The only way I'd ever put one in my own home is if I didn't have any room, which isn't likely.

    I'd go high efficiency boiler/heater.
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  3. #3
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Yakima WA


    There are those who are 100% sold on tankless water heaters. This is inspite of considerable evidence indicating they are more costly over the years than conventional heaters. This section of the forum was created because of this controversy. There are many factors to consider including the temperature of the incoming water supply in the winter, size of your gas or electrical service, available service people, and more. I would strong urge you to research these things carefully before investing thousands of dollars in a tankless heater.

  4. #4

  5. #5
    In the trades Dana's Avatar
    Join Date
    Jan 2009


    If you have a 20+ year old boiler going with the boiler replacement w/indirect is absolutely better than any tankless solution, on cost, efficiency and payback.

    DO make sure you size the boiler properly for the load. Going from a 3x oversized to perfect or even 1.5x size will cut fuel consumption dramatically. Whether you go with a condensing vs. mid-efficiency boiler depends on the average water temp the radiation needs, but getting it sized right is the first 80% of the solution.

    Play around with this tool a bit (derived from Brookhaven Nat'l Labs test data)



    You may have to do your own fudge factors between oil/therms, etc. But if you can calculate your actual use against degree-day data the accuracy of the tool is way better than a Manual-J calc.

    A right-sized modulating condensing boiler with a well insulated indirect will probably cut your fuel consumption by at least a third, maybe as much as half.

    A tankless definitely a 2nd rate solution if you have a decent hydronic boiler. If you have the space & things are located reasonably, installing a drainwater heat recovery system on the main shower at the same time converts a boiler-backed indirect into an "endless-shower" water heater (but not endless tub-filler), with none of-the competing flow issues you get with a tankless. If you go with a "reverse indirect" that buffers boiler water, with an internal heat exchger for the potable hot water, (eg. TurboMax, ErgoMax, Everhot EA) plumbed as a buffer tank for the entire heating system, that's usually good for double-digit savings on fuel consumption as well by minimizing cycling losses during partial heat-load conditions.


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