Going to on-demand gas heater, what to do with tank?

The Tank Going to on-demand gas heater, what to do with tank?

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  • #24332
    qdllc
    Participant

    After years of living on an electric hot water heater, we decided to go with a gas on-demand system. The tank did fine, but we had one application where it would run out of hot water (hot tub), so we couldn’t enjoy it.

    I’ll start by saying I do not want to remove the existing tank…at least not at this point. It’s behind other water treatment items, so I’d have to undo a good deal of plumbing to pull the unit out. Removal will be withheld until I have to take stuff apart anyway.

    I know it’s better to have the unit full rather than empty. However, I had the thought to divert the cold water flow through the tank so it’s always being “flushed”. I’m attaching a crude diagram of my idea.

    As you will see, I’m thinking of using cutoff valves on the cold and hot water lines to divert through the tank as well as a cutoff on the bridge from hot to cold should I want to put the tank back into service making hot water. If I pull the unit entirely down the road, I’d just cap the hot water line and redo the cold line.

    The new heater is installed later in the chain and not depicted here.

    Thoughts and advice?

    Attached files

    #24334
    Larry Weingarten
    Participant

    Hello, The normal bypass valving is a bit different than what you show. I’d put a valve on each side of the heater and then extend those lines up to a horizontal line. Put a valve in the horizontal line between the two verticals. Now you have a system that lets you use the tank (or not) and lets you bypass and drain it as well.

    Another thought is to put a tankless heater to serve only the tub, and leave the rest alone. This likely will give you better hot water service for the majority of the fixtures.

    Yours, Larry

    #24340
    SolarBill
    Participant

    … Another thought is to put a tankless heater to serve only the tub, and leave the rest alone. This likely will give you better hot water service for the majority of the fixtures.

    Yours, Larry

    Hi qdllc,
    Larry has offered you a very viable solution. I would amplify that solution to allow you to back-up the entire house with either hot water source, should one heater fail.
    Essentially, you put a shutoff in the hot water side to isolate the spa tub from the rest of the house and feed the spa tub with the tankless. When either fails, you isolate the failed unit and open the isolation between the spa and all else.
    Please install the tankless as the manufacturer suggests, paying particular attention to gas supply and venting. Remember to install service valves and utilize them when the scale issue becomes evident.
    Best,Bill

    #24341
    SolarBill
    Participant

    qdllc wrote:

    I’ll start by saying I do not want to remove the existing tank…at least not at this point. It’s behind other water treatment items, so I’d have to undo a good deal of plumbing to pull the unit out. Removal will be withheld until I have to take stuff apart anyway.”

    Hi Again adllc,
    This is for you and any other reader who might be inspired to do a bit more planning and not allow equipment to be installed that hampers service or removal of other equipment. In today’s economy it is unfortunate that one trade doesn’t respect another trade but that is the situation. It is doubly disappointing/unfortunate that an allied trade does the same thing. Your water conditioning people likely could have positioned the equipment to allow independent service of all equipment w/o interference. It might have been more work and accordingly, more expense. What would you choose now?
    Thanks,

    Bill

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