Purchase Advice Tankless or Tank

Discussion in 'Tankless Water Heater Forum' started by Bnick, Sep 9, 2018.

  1. Bnick

    Bnick New Member

    Joined:
    Sep 9, 2018
    Location:
    06484
    Hey All,

    I am a new homeowner and the current water heater that I have is out of warranty and has a gas leak issue 50GAL A.O. Smith. I live in CT and have a 3500 sqft home with 4.5 baths (master has a jacuzzi tub and a 6 head shower), dishwasher, washing machine. The question I am looking for your professional advice on is should I change the tank water heater to another tank but larger or do I go tankless where I would probably need two to keep the flow rates consistent in the winter?

    I will try to answer any technical questions as best as I can.

    Thanks for any help you can provide.

    Bnick
     
  2. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    I would go with a 75 gallon gas water heater and perhaps a tempering valve. It's difficult to fill large tubs or run multiple showers with tankless.
     
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  4. Bnick

    Bnick New Member

    Joined:
    Sep 9, 2018
    Location:
    06484
    Awesome Thanks for the advice Terry.
     
  5. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    A six head shower would bring any tankless to it's knees, and could drain even 75 gallon standalone pretty fast too. (Even at 1 gpm x 6 heads it'll deplete a 75 gallon tank in under 12 minutes.) Boosting storage temp to 150-160F and tempering it down will helpe, but not enough.

    If (like many homes in CT) you're doing your space heating with a boiler you may get better service out of an indirect fired water heater running as a "priority zone" on the boiler. Sizing the tank for the largest tub you need to fill is appropriate, but recovery rates matter too. A boiler heating a 3500' house in CT would usually have twice the BTU output/ half the recovery time of a standalone. In the past CT has offered rebate subsidy for installing an indirect water heater- not sure it that's true this year.

    If the deluxe shower gets used more than five minutes per day it may be worth investing in a drainwater heat exchanger, which can roughly double the "apparent capacity" of your water heater for showering, but not for tub-filling.

    [​IMG] [​IMG]

    It doesn't have to be located next to the water heater (though that makes it easier to plumb), but it DOES have to be downstream of the shower drain, and vertical. A 4" x 48" or larger would return about half or more of the heat going down the drain into the incoming water stream, cutting your BTU rate in half. The longest and fattest that fits has the quickest payback, since the marginal cost of the unit isn't huge compared to the fully installed price- the labor is about the same for a 3" x 30" heat exchanger as it is for a 4" x 96" that returns a LOT more heat.
     
  6. Bnick

    Bnick New Member

    Joined:
    Sep 9, 2018
    Location:
    06484
    Hey Dana,

    Not sure I fully understand that setup but the 50Gal didn't have much issue unless multiple showers were going for longer than 15 mins so a 75 that Terry recommended seems to e a good fit in my novice judgement.

    The last question I have for you guys is the plumber I am working with is recommending a free air High-Efficiency 75Gal Rheem vs a Combustion air model, do you guys have a preference? The PVC for intake and Out is already set up from the current water heater.

    Thanks again.

    Bnick
     
  7. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    A modulating condensing all-stainless HTP Phoenix PH100-80 (100KBTU/hr burner, 80 gallons) can sustain a continuous 24/7 full-flow shower with margin, and will outlast any glass-lined 75 gallon water heater by at least 2x in a residential application.

    If the 50 gallon was almost cutting it and big enough to fill the tubs, the Phoenix PH100-55 (100KBTU/hr x 55 gallons) would be a better choice. It's the same burner to support but with only 55 gallons of buffering capacity. Even though it's nore than twice as expensive as a glass lined 75 gallon water heater, it's "worth it"- you'd only pay for the installation once every 25+ years instead of every decade .

    The Phoenix Light Duty PH76-50 (only light duty in terms of commercial water heater burner size) has a 76K burner. The Westinghouse branded version of the 50 gallon version runs about 2 grand at Home Depot, but your plumber might be able to beat that price on the HTP labeled version buying direct from HTP (they're located in MA.) It's twice the burner output of a typical 50 gallon standalone, all stainless just like it's bigger-burner siblings. If your old water heater almost cuts it, the 76K burner can squeak out a single shower forever, but not with as much margin for other simultaneous uses as a 100K burner.

    Or, you can save that money and go with a standard 50-55 gallon standalone, and apply the savings toward a drainwater heat recovery heat exchanger.

    A drainwater heat exchanger takes heat out of the water flowing down the drain and puts it into the incoming water stream. That incoming water stream is feeding both the water heater AND the cold side of the shower mixer with much warmer water than what's coming in at the street, so it takes slower sip of hot water from the 120F+ tank to deliver 105F water at the shower head, and the water heater has to put less heat in to keep up. With a 4" x 48" or larger heat exchanger a standard 50 gallon tank with a standard 36-40KBTU/hr burner can support an almost continuous 2gpm shower most seasons at CT incoming water temperatures. From a showering perspective it's like doubling the size of the burner, but a burner that burns no fuel.

    There is some pressure drop from the flow through the heat exchanger, and they're not all equal. For almost a decade Renewability's Power Pipe series (available in the US, but you can also buy direct from the manufacturer), but more recently EcoDrain's V1000 series completely at their lunch on both recovery efficiency and low pressure drop at high flow. A 4" x 48" V1000 returns 57% of the heat back to the incoming water stream at a standard 2.5 gpm flow rate (part of the Canadian standard test conditions) a bit more at lower flow, a bit less at higher flow. (The 4" x 72" returns fully 2/3 of the heat back, well worth it if it fits.) By comparison a 4" x 48" PowerPipe returns 49.8% which is still pretty good compared to the other competitors in this market. (I have about 10 years of service on a 4" x 48" PowerPipe in my house in MA and am totally satisfied with it's performance). As they grow taller the performance difference between those series becomes more pronounced.

    But it'll increase the "apparent capacity" of the tank in showering mode by more than 1.5x (more than 2x with a 4" x 72" V1000), but does nothing for tub filling capacity, since the drain isn't flowing when the tub is being filled. But if a 50 gallon tank fills your tubs, this would be a better overall investment than a bigger tank with a bigger burner.

    For a 4" x 48" or 4" x 60" expect to pay about a grand for the unit. If you have room for a taller one the marginal upcharge is worth it- the tallest that fits is the "right" one. If it saves you a grand on water heater by letting you stick with a 50 gallon tank it's pretty much paying for itself up front, but in families that primarily shower it'll also pay for itself (installation included) in under a decade at CT's higher than national average retail natural gas rates.
     
    Last edited by a moderator: Sep 16, 2018 at 6:22 PM
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