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Thread: Installing a 3 gallon heater ca?----

  1. #16
    In the trades Dana's Avatar
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    Water that you've paid to pump from a deep well is complete waste if you're dumping it in your septic leach field to replenish the shallower water table. It's diluting the septic system too, lowering it's effectiveness. Only if it's being directed to a greywater system used for toilet flushing or garden watering would any value be retained.

    The standby losses of an electric under-sink tank may be lower (often MUCH lower) than the heat abandoned in the plumbing by a recirculation approach. It depends a lot on the total volume and individual draw volumes at that tap. Either way you do it, insulating as much of the hot water distribution plumbing as is reasonably possible with 5/8"-wall pipe insulation is cost effective in most places. The plumbing insulation primer lives here.



    If you're filling 50' of 3/4" plumbing (~1.25 gallons) with 130F water to get a quarter cup for wetting a sponge the recirculation solution is an energy-disaster, a HUGE step in the wrong direction.
    Last edited by Dana; 07-05-2011 at 09:02 AM.

  2. #17
    Retired Defense Industry Engineer jadnashua's Avatar
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    If you set it to only run when needed and you can afford to wait for the pump to get the hot there, it will be cheap. It's still not all that horrible if you pipes are insulated, depending on where they run (conditioned space, verses unconditioned).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #18
    Moderator & Master Plumber hj's Avatar
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    The problem with the "redi temp" units at the sink is that the "thermo valve" is IN the pump and when it goes bad, as it will eventually, you may have to replace the entire unit. The Grunfos "comfort" system has the pump at the water heater, and easily replaceable control units under the sink. In addition, if your home does NOT have a linear system where a single valve takes care of ALL the sinks, you can install additional ones at the other "remote" sinks, which you cannot do with the pump under the sink.

  4. #19
    In the trades Dana's Avatar
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    For a tap that's primarily used for short or very-short draws, a recirculator is a more complicated and less energy efficient solution than a point-of-use mini-tank in series with the outflow of the main water heater. If the distribution from the main heater is so long that you'd even contemplate a recirc, the volume of hot water abandoned in the distribution line exceeds the draw volume by an order of magnitude. With a mini-tank the abandoned volume equals only the draw volume, not 10x the draw volume, but there is a standby loss introduced. With insulated input & output plumbing on the mini-tank the standby losses are extremely low.

    Of course it's difficult to model the performance in actual use without all of the relevant information. We should set up data loggers and track draw volume, frequency & temperature of the draws from that tap for a month or so, THEN decide which approach makes more sense based on real info rather than a WAG! :-)

  5. #20
    In the Trades Gary Swart's Avatar
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    In my opinion, if you can install a dedicated return line, it's a no-brained. I realize that access is not always easy and might involve more demo and repair work that you would want to do. A retro fit device would be the simplest to use, but as others have noted, these have their disadvantages. As far as operating costs are concerned, I run my Laing pump 24/7 and have done so for about 8 years. I'm sure there is a cost for that, but my power bill is not excessive. It would be easy to put a timer on it, and of course there are pumps with a timer built in. I just figure what little added cost there is, is worth it to have instant hot anytime I want it, and yes, sometimes I do want hot water a 2 or 3 AM.

  6. #21
    DIY Member bsa_bob's Avatar
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    Ijust had it in my head that i was wasting water,the waiting isn't bothering me to the point i will not wait!! for hot water. Its the thought of maybe spending thousands of dollars down the road redrilling my well, Although my well is one of the deepest on my block-so to speak bob s

    Maybe i'll just pass on this "hotter " issue./i have been here 20 years and have not noticed any slow downs yet in my water pressure. What do you think??

  7. #22
    In the trades Dana's Avatar
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    It's fairly simple math to figure out how many gallons you'd be wasting on a first-draw at the remote tap using the diameter of the plumbing and the distance from the HW heater. On subsequent draws it's a matter of how much of the abandoned heat remains in the distribution plumbing. Compared to what you'd waste with a leaking or old-school high volume toilet it's probably pretty minimal. With 3/4" plumbing is about a gallon or so for every 50' of pipe, with half-inch it's a gallon for every hundred feet, as a very rough order of magnitude. If it's primarily the water savings you're after, do a bucket-test on your shower flow (or just replace the shower heads with a super-sipping 1.5gpm type) and swap out any 3-5 gallon flushers remaining in your toilet fleet for a noo-skool 1.6 gallon version.

    More than well-failure issues, water conservation has a bigger impact on septic systems, where excess volume/dilution tends to reduce function and shorten lifespan.

  8. #23
    Retired Defense Industry Engineer jadnashua's Avatar
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    Most faucets are flow-restricted, so even with a half-gallon, it could take 20-30 seconds to get warm there, and a little longer to warm up the pipe so you can achieve full hot. Something like a vanity faucet may be restricted to in the order of 1.5gpm. Personally, with my recirculation system, it only warms the cold line part way back to the WH. If I flush a toilet, that purges essentially all of the warm water in the line, and restores it to as cold as it gets. A dedicated return line keeps the cold line always cold, but in my situation, it's not an issue. So, with a retrofit unit, most of the issues can be managed. And, they do make demand switches, so that the thing only runs when you need it, or timiers that can be set to choose a time of day you want hot quicker.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  9. #24
    In the trades Dana's Avatar
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    Yabbut Jim, he doesn't really care about the wait, or even the energy use- it's about the wasted water. If he's flushing the toilet to purge of the tepid water his primary goal has been defeated (with prejudice!).

    There are better trees to bark up than the wait for hot water, since we're probably talking less than 3 gallons/day of waste here. That's about the difference in between a 5 gallon vs. a 1.6 gallon toilet in a single flush, and an order of magnitude smaller than 10 minutes of 4gpm vs. 1.5gpm showering.

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