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Water heater thoughts/ideas

Isengrim | Posted in General Questions on

Hey there all,

I’m living in an older 1100 sq foot two story home with basement in Zone 4 that has both geothermal heating and a solar roof.

Recently, the galvanized steel water line going up to my upstairs bathroom started experiencing a slow leak from corrosion, and I’m looking to rip up the floor in the bathroom to replace the entire line. 

I also currently have a tankless gas heater that’s 7 years old, and while I clean it maybe once a year, I’ve never been very impressed with its performance (particularly running upstairs, as it takes a while to detect use and cycle on). Additionally, it’s the only device in my home on the natural gas line and it would be nice to remove it and end that service charge on my bill.

I’d considered going with POU electric water heaters upstairs (sink & shower) but I’m afraid that with both solar/geothermal already in terms of overhead, I may max out the breakers in my 200 amp box. Is it still doable? Should I look to upgrade my panel?

Given I have geothermal, should I consider a desuperheater instead, or maybe some combination of desuperheater and tankless electric (such as in this article: Is there something else that I’m not considering?

Thank you in advance for any thoughts/advice.

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  1. Expert Member
    BILL WICHERS | | #1

    You’re unlikely to overload a 200A panel with any kind of normal household loads. I honestly think (and I’m an electrical engineer) that the people pushing “400A” services just want to sell you something. Typical residential electric services are only actually 320A on a “400A” service, and the utility will usually feed them with a 25 or maybe 50 kva transformer which is either 104 or 208 amps, respectively.

    Anyway, electric tankless water heaters ARE very large loads, often up to 100A or so. This is why they are considered to be particularly grid friendly. Point of use water heaters will use significantly less power if you want to go that route.

    So you really need a tankless water heater? Can you maybe use a heat pump water heater instead?

    One last bit of info for you too: if you do install one of the large electric tankless water heaters using a 100A circuit, or something close to that, there is some fine print on those big circuit breakers. While a “100A” breaker is rated for use with a 100A load, the SPACES in the panel are often only good to around 120A or so per space. This is important because the two breakers opposite the “big” 100A breaker in the panel share a piece of the busbar in the panel. Many people, including myself, like to group all of the double pole breakers together in the panel. This means you might end up with a 50A range breaker opposite your 100A water heater breaker and you will have the possibility of overloading the ~120A or so busbar stab in the panel and there is NO PROTECTION for those stabs in this case! Always be sure if you’re using a large breaker like a 100A breaker that you only put small branch breakers (15A, ideally) on the opposite side from the big breaker.


  2. Expert Member
    NICK KEENAN | | #2

    With geothermal, I'd be thinking of ways to use some of that geothermal heat to heat the hot water.

    In summer, your system is producing waste heat that can be captured. In winter it's pulling the cheapest heat around out of the ground. What makes sense is going to depend upon the specifics of your situation. Here are some ideas, some crazier than others:

    * Add a water-to-water heat pump using the same geothermal loop. In the summer, have the output of the AC heat pump feed its input. In the winter have them run independently in parallel.
    * Use a heat pump water heater and position it so that in the winter a heat register blows on it and in the summer its exhaust flows into the return of the AC.
    * Add a storage tank with a desuperheater ahead of whatever water heater you decide on.

  3. tommay | | #3

    Before you change out your HW heater, see what condition those galvanized pipes are in. If they have corrosion built up inside, that may be part of the problem of why your hot water takes so long to get there..replacing the lines may change things.

  4. Expert Member
    Dana Dorsett | | #4

    >"...hould I consider a desuperheater instead, or maybe some combination of desuperheater and tankless electric ..."

    Desuperheater maybe, tankless electric, absolutely not! Even point of use tankless heaters are abusive to your very-local power distribution grid, with short bursts of VERY intense power draw, making it difficult to maintain decent power quality. A tankless water heater's instantaneous draw is likely to be a multiple of what your geo is pulling. Even the smallest electric tankless that would deliver sorta-reasonable hot water performance as a whole-house water heater would need ~100A @ 240VAC, half your breaker. A 2 gpm shower at a mid-winter 60F temperature rise would draw ~75A @ 240VAC, with very little extra capacity for other hot water use.

    At the current upfront cost & improving performance of heat pump water heaters the desuperheater + finish-heater approach is making less and less economic sense. Simply sizing the tank for the biggest tub that it needs to fill works for most households. The additional efficiency gained by going with a desuperheater is sort of "in the noise", but the additional installed cost is non-trivial.

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