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Thread: Need help deciding tank or tankless . . .

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  1. #1
    DIY Junior Member paulmiller's Avatar
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    Default Need help deciding tank or tankless . . .

    Iím thinking of getting a tankless water heater to replace my aging gas tank heater.

    What should I look for and what should I look out for?

    I'd like to hear form anyone who owns and has used one either gas or electric (I'm open) for a year or more.

    Thanks!

    Paul

  2. #2
    In the trades Dana's Avatar
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    A 199KBTU/hr gas fired tankless is great if you have a huge soaking tub or spa to fill! Most electric versions have limited output, and even then you'd need a dedicated 100A 240V service for the electric tankless to have decent tub-filling times for standard sized tubs at northern CA incoming water temps. (It matters!)

    The cost of heating water with resistance electricity is usually substantially more than heating with gas too- comparable to heating water with propane, but it just depends.

    The ignition delay on some gas fired water heaters can be an annoyance, especially in cold-water country, since a slug of water gets by the heat exchanger unheated on successive draws so you end up adjusting then re-adjusting the mix at the tap a couple of times per draw. (google the phrase "cold water sandwich" ).

    They don't take up much space, the output and efficiency is good, but only the highest-volume users would ever make up the difference from a financial point of view at current natural gas pricing. In hard water country it's often necessary to de-scale the heat exchanger annually- not tough to do if you plan (and plumb ports) for it, but it's a maintenance issue you don't have with a tank, and if you're paying somebody to do it the economics of the higher efficiency flat out fail.

    The (not such a bad) compromise position is to go with a 40-50 gallon condensing gas fired tank, which is simpler, typically doesn't require upgraded gas plumbing diameters or an upgraded gas service (if you go with a 76KBTU/hr Vertex rather than the largest-burner Polaris), and still puts out way more first-hour gallons than any atmospheric-drafted gas water heater of comparable size (or burner size.)

    I'm neither a fan of, nor do I despise gas-fired tankless, but when I replaced my heating system boiler I went with a different approach retiring my tankless early (only 14-15 years of service- might have gone another decade), using the heating system to heat my hot water. I'll still never run out of hot water in showering mode (an important consideration for my family- YMMV), but it's only so-so on tub filling times compared to a tankless. As configured the new approach improves the space heating efficiency of my now micro-zone house, which was a primary reason for the change- the tankless was doing just fine as a water heater, despite having temperature control issues at very low flow. (If low flow temp control is important to you, look for smaller minimum-BTU numbers for any given model, and stick to Noritz or Rinnai, either of which have better than average temp control even at min-fire.)

  3. #3
    DIY Senior Member lifespeed's Avatar
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    Some things you will have to consider for a gas tankless (forget electric, it's very expensive to heat water that way): Can your pipes supply, or easily be upgraded to supply 200K BTU of gas?

    The scaling issue applies to both tank and tankless, both will suffer an efficiency loss. But with the tankless it is imperative to de-scale or it will lose so much efficiency as to degrade function and lifespan. A water softener can be a good solution that has great benefits for the rest of your plumbing as well.

    I chose to go with a 200K BTU Noritz and a water softener with a recirc pump on a timer and pushbuttons throughout the house. The results have been excellent. The heater lights off at all but the lowest of hot water flow rates. The cold water sandwich effect is almost non-existent, more of a slight fluctuation from hot to warm. I attribute this to a fairly quick start of the heater, and 1" plumbing with enough volume to mix the "sandwich".

    Tankless are not miracle appliances, but they do excel at endless hot water, simultaneous showers, etc. I would point out one key detail: if you want high flow on the hot water side get the largest Noritz because it has minimal pressure drop across the heat exchanger. The Gallon Per Minute rating does not tell the whole story, look at the pressure drop also. Model NRC1111 shines here.

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