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Thread: tankless hot water heaters

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  1. #1

    Default tankless hot water heaters

    I'm trying to decide between a convential hot water heater and a tankless hot water heater for my new house. The house has two bathrooms and each bathroom has a shower and a bathtub. One bathtub is actually a whirlpool tub. The tankless model I have been looking at provides water at about 6 gpm. Is this less than that provided by a conventional hot water heater? What are the pros and cons of tankless hot water heaters and what do I need to know? There would usually be two of us living in the house but I don't want to run out of hot water if using dishwasher and shower, or washing machine and dishwasher and tub. Any information on this would be helpful.

    Thanking you in advance.

    Burzmet

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default heater

    You are confusing apples and oranges. A conventional heater will furnish as many gpm as the pipe and faucet will allow, until the tank is empty of hot water. The tankless will furnish hot water at that gpm. If you try to exceed it, the heater will either reduce the demand to that level or the water will flow through too fast to be heated and then you have warm water.

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    Plumber Cass's Avatar
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    Will it be gas or electric and do you live in a hard water area?

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    Master Plumber Redwood's Avatar
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    The tankless is 6 GPM at what rate of rise? If your winter water temp is 34 degrees f then the 6 GPM may actually be 1.5 GPM.

    A tank type water heater will give you 70% of the tank capacity of hot water. A tankless will give you hot water up to its capacity based on the incoming water temperature until you shut the hot water off.

  5. #5

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    You said that a tankless will give you hot water up to it's capacity... If the ambient water temp is 40 degrees F and I am filling a bathtub with water expected to be at 105 degrees will the gpm of the tankless heater be the same as when the ambient water temp is 60 degrees? Does ambient temp of city provided water change all that much (maybe some simple education on how the tankless works would help me understand all this)?

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    Moderator & Master Plumber hj's Avatar
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    Default heater

    The tankless heater will give a certain amount of water a finite temperature increase. If the water flows faster than the maximum design, then the water will be cooler than anticipated. If the incoming water is colder than the design temperature, then the outgoing water will also be cooler than anticipated. For any given incoming temperature, there will be a specific gpm that will produce the desired water temperature, and since the means to compensate for the variation is not automatic, the user will have to reduce his usage flow when the incoming water is below specifications.

  7. #7

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    It will be gas and the house is in Colchester, VT (just north of Burlington, VT). I don't know the water condition but we are not installing any water treatment unit and it is city water (as opposed to well water).

  8. #8

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    What is the gpm of a typical bathtub faucet with typical piping using city provided water (as opposed to well water)? I guess to put the question another way, what is a good gpm rating on a tankless water heater for a house where it is usually two people (but sometimes more), two bathrooms, both with showers, tubs, and sinks, a dishwasher, and a washing machine?

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