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Thread: 2 water heaters, series or parallel??

  1. #1
    DIY Junior Member macingrace's Avatar
    Join Date
    Dec 2012
    Cheyenne, Wy

    Default 2 water heaters, series or parallel??

    This may get jerky, I have tried to put in all information I can think of, probably scattered in thought though. I hope you can read it and make sense of it all.

    Currently 1 40 gallon electric water heater. I am replacing with a 50 gallon gas. When this is done I want to put a electric 40 gallon in master bath I got for $30 brand new. I will use existing circuit to power it. What I want to accomplish:

    MB is about 90 feet away from water heater. With circulating pump installed takes about 1 to 2 minutes for hot water to hit bathroom. Without pump it can take up to 4 or 5 minutes. I have no issues of running out of hot water. I just want to set up 2 water heaters so I can remove pump and get hot water faster to MB. I also want to do this the most efficient way possible.

    My thought is to supply MB (2nd) water heater with the hot side from the 1st water heater and this will save me money not having to have the electric heat as much water. The first will supply the rest of the house as they are all within 10ft and only as far away 25 feet of 1st water heater. I believe the circulating pump in my case is costing me lots of electricity. I am just looking to get hot water to my MB quickly and saving money on utilities. If I supply cold water to MB it would seem to me this is more expensive as I have a gas WH heating cold water and the electric doing the same.

    Any thoughts on this? Anything else I need to know to do this correctly??

    The circulating pump is connected to the faucet under the sink in the MB. This was done per instructions with pump. It is set to come on and off 3 time zones a day, early mid and late.
    What would be a better way to install. As stated all connections are made right under the sink as the instructions told me too.
    I do have access to all plumbing in crawl space.

    The circ pump is a Laing AutoCirc Pump, mad by Laing Thermotech, Inc.
    I have also added a picture of the circ pump under the sink in my MB. I hope this helps in some way.

    The circ pump is hooked up per instructions, I can hear it running and yes, it has electricity directly behind it into a closet, it cannot be seen under the sink. I have run it on Auto until the last month or so I changed to timer, thought I might save a little money?? Without the circ pump hot water takes 3 to 5 minutes to reach sink, with it 1 to 2 minutes. So it makes a huge difference, just not as fast as I would like.

    I did think of one more thing, not sure if it would effect it or not. The cold water line in the crawl space under the MB has been tapped and is supplying water to my out building. This is approximately 200 feet away. The outbuilding has its own water heater. There is a small apartment built there my son lives in.
    Would the pump be trying to supply the out building with hot water as well? This was the closest place to get water to the out building. There is a 1' line tied in there. The house is on a 3/4 inch line.
    If this does cause issues, then a hot water heater may be the best answer?

    I should mention I have the water heaters available and paid pennies on the dollar for them. I bought 2 50 gallon gas water heaters for $100 each scratch and dent with 12 year warranties at a local store. I also bought a 40 gallon electric, never installed, for $30 at a local store going out of business. So the cost of the water heaters is negligible.

    I just want to have hot water sooner after it is turned on.

    Thanks for your help.
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  2. #2
    In the trades Dana's Avatar
    Join Date
    Jan 2009


    It doesn't take anything like 30 gallons of dilution water on the local end to avoid the slug of cold/tepid water from dropping the output temp of the local water heater to below showering temperatures. With 3/4" plumbing you're only talking a couple of gallons of water, with half-inch it's about a gallon. You could probably do just fine with a 10-gallon heater on the MB end when plumbing them in series. But since you have the 30 gallon version and the space, go for it!

    With short-draws for hand washing etc the hot water from the gas heater never arrives, and that heat is abandoned in the line, and quite a bit of the water heating will be electric, but during bath or shower draws it will be substantially from the gas heater. By getting rid of the recirc you'll be abandoning LESS hot water in the pipes than with the local tank though.

    Insulating the hot water feed from the gas-fired tank means you'll be losing less to the crawlspace, for a higher-fraction of gas heated water overall. Don't cheap-out with the crummy R2 goods (3/8" wall) found at box stores- go with R4 or better 5/8" or 3/4" wall stuff, even if you have to seek it out. Plumbing supply houses may carry it, but if not the local supply house, Graingers or internet stores sell it. Some TrueValue Hardware stores carry the fat stuff for half-inch plumbing, but not for the 3/4" plumbing. Given you have 90' of distribution plumbing in crawlspace it will pay to get the better stuff.



    Last edited by Terry; 12-11-2012 at 03:44 PM.

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