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Thread: Water heaters in series

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    DIY Member jimmym's Avatar
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    Nov 2005
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    Default Water heaters in series

    OK, I've done a search, but haven't come up with a situation like the one I'm about to try. I know the whole "two water heaters" subject has been beat to death, but...

    I have an 80 MBtu oil fired boiler. It has a tankless coil built in. Normally, it's just about adequate. However, when filling our tub, the flow is too great and the water ends up being only luke warm. The boiler will run and shut off at its setpoint when filling the tub. The boiler can meet Btu requirements to re-heat its own tank, but the tankless coil can't get the Btus out fast enough.
    Our shower/tub valve is a single knob that goes from off->cold->warm->hot. It doesn't really let you throttle the flow. Anyway, the tub would take forever to fill.

    Here's what I'm thinking...

    Cold supply-->Boiler Coil-->Tempering valve (130 Deg)-->Tankless electric (120 Deg).

    Under normal conditions, the tempering valve will reduce the boiler coil water temperature to 130. The tankless electric will see flow but because it's over its setpoint it doesn't turn on. Under high flow, when the boiler can't generate 130 Deg water, the output of the tempering valve will drop and the electric tankless will kick in to maintain 120 deg output.

    What do you think about Eemax electric tankless heaters?

    Thoughts?
    Last edited by jimmym; 02-01-2006 at 05:35 AM.

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