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Thread: What water heater for a limited space

  1. #1
    DIY Junior Member Dom Z's Avatar
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    Default What water heater for a limited space

    I'm remodeling my bathroom and putting in a new shower spa system.
    It's a Moen 275 system.

    I've been told to run at least 3/4" supply lines for the shower systems.
    I've turned the water on with my current setup and seem to get plenty of water and pressure.
    I'm not a plumber just a DIY guy so I don't know hydraulics. I do know I can't afford a plumber. At least not the ones in NJ.

    My current supply lines both hot and cold are 1/2". The cold T's off a 3/4" to a 1/2" so I think I can replace the T and be OK.
    The hot supply comes out of a coil in my oil fired furnace and has a 1/2 connection both in and out.
    I'm thinking of installing a small hot water heater just for the shower system.

    However, I only have a very small space to install one. Plus, there is no NG in my area and I really don't want to have a LP tank installed.
    So that leaves me with either an oil fired heater or an electric heater.

    Are there any electric or oil fired heaters on the market that are made for a small space Say 24"X 24"X 48"

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    Retired Defense Industry Engineer jadnashua's Avatar
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    What are the gpm requirements for the spa?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member Dom Z's Avatar
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    I think the biggest demand will be from the 4 body sprays they're rated at 1.5 GPM. That's a total of 6 GPM at any one time.

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    In the trades Dana's Avatar
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    A 40 gallon Reliance 6 40 DJRS will just squeak in there, but it'll be tight (44" tall , 20.5" in diameter.) See: http://www.reliancewaterheaters.com/.../R616E1207.pdf

    I'm sure other manufacturers will have mid-height versions of similar dimensions, but you'd be lucky to find a 50 gallon flavor that actually fits.

    That won't give you much tub filling capacity if it's going into a soaking tub or jacuzzi, and back-to-back showers will be all but impossible with a 6gpm gusher. But you may be able to fix the showering time limitation:

    If it's accessible/reasonable you can roughly double the shower time capacity of any tank heater with a drainwater heat recovery system (eg GFX, PowerPipe), but you'll need at least a 48" vertical section of drain to cut into to get one that has sufficient performance at 6gpm. They're not super-cheap either, but will pay for themselves in power savings within 5 years in most places. (In high electric rate areas, it can be as little as 2 years.) They don't do squat for tub filling capacity since the drain and water have to flow at the same time to get the benefit.

    It's like adding a roughly kilowatt or so of element that is continuously "on" while showering which reduces the drawdown rate (since you're mixing in less hot water to get tepid-not-cold water up to temp) and reducing the tank recovery time (since instead of heating 40-55F water up to 120F it's starting with 65-80F water.) Best part is, it's a kilowatt source that isn't spinning the meter. If the plumbing & drain layout is at all reasonable for hacking it in, a drainwater heat recovery system can be a marriage-saver when you don't have room for a bigger tank. ;-) Fatter & taller is always better- if space is limited even a 36" x 4inch drain does a world of good- significantly more than a 48" x 2-inch drain version. If you have all the headroom in the world and can stuff a 60" x 4" in there you're golden.

    See: http://www.renewability.com/uploads/...e_retrofit.pdf

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    DIY Junior Member Dom Z's Avatar
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    Actually there isn't a tub just a 60X34 shower. So I don't have to be concerned about tub filling.
    The shower head is rated for only 2.5 GPM. It's the 4 body sprays that are gushers and they shouldn't be used much.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Keep in mind that you won't get the full volume of the tank...as the cold replaces the hot, it cools things off. The thing to look at in the specs is the first hour supply. At 2.5gpm on the main showerhead, I think on a 40g tank, you'll start to notice it cooling off in 10-min or less. You may want a thermostatic controlled valve if you don't have one.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member Dom Z's Avatar
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    Would a tankless work in this application?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    A correctly setup tankless system could work, but it won't be cheap with a fair amount of volume you are requesting. A properly setup tank would too. My personal, limited experience with tankless was less than stellar. They can work, but aren't the panacea people think they are. There's a lot of misinformation out there, and finding someone who can design and then service and install it properly is still spotty. Most guys can get it working, but you may not have something that does what you want and need. same's true with a tank, but since they are simpler, you don't have as many problems. you can also get someone to service it on the weekend when it eventually dies. Spotty with a tankless, if you can find anyone at all.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the trades Dana's Avatar
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    Quote Originally Posted by Dom Z View Post
    Would a tankless work in this application?
    An electric tankless that would handle the side-spray volumes would probably require a significant upgrade to your electrical service.

    A 40 gallon tank w/drainwater heat recovery would do pretty well. Testing by the Canadian government demonstrated that properly plumbed, a maximum of 28 minutes of shower time for a gas-fired tank at a standard flow rate was nearly doubled to 53 minutes with a 36"x3-incher, and more than doubled (over 74minutes- they stopped the test at 74) with a 60" x 3 inch unit. See Table 4 in this document:

    http://www.gfxtechnology.com/NRCan-3_24_06.pdf

    more info:

    http://www.regie-energie.qc.ca/audie...2_28sept07.pdf

    Results from other testing & modeling by the US DOE, and the Canadians a 48" x 4-inch has similar performance to a a 60" x 3-inch- it's all about the amount of contact surface area between the potable water pipe wrap and drainwater pipe- fatter & longer is always higher-performance. The longes versions have pressure drop issues at higher flow, but some designs (notably PowerPipe) have gone out of their way to minimize that issue.

    With an electric tank the time you'll need the longest 3" version to roughly double the showering time, because the amount of heat going into the into the water from the elements on at typical electric tank is only about 1/5 that of a typical gas fired tank. But even with the power off, by increasing the temp of the cold water feed from 40F up to 75F with drainwater the flow from the hot side to get get the shower temp you want is cut in half- it truly is a ~2x extender. And by feeding that same 75F water into the tank's cold input the internally mixed water is warmer longer, and it's recovery time is cut significantly.

    Basically, you can get by with a heluva lot less tank if you recycle the heat from the drain. At 6gpm you're sapping the efficiency somewhat- using data from older versions modeled by the DOE in the 1980s, a 60"x 3" goes from ~50% efficiency at 2.5gpm to the ~43% range at 5gpm and a 60" x 4" goes from ~58% @ 2.5gpm to 51% @ 5gpm see figures 1a & 2a, the G3-60 & G4-60 curves:

    http://www.gfxtechnology.com/EFF.pdf

    Those being shipped today are somewhat better than those in the model, but the shapes of curves haven't changed much.

    You'd pay more for the heat exchanger than for the tank, but the performance result will be worth it when you're limited by space. It's cheaper than an electric tankless even WITHOUT factoring in the cost of the service upgrade so that your panels & wiring can handle the peak current. Unless you're heating with a large heat pump you'll likely have to make significant power service upgrades to handle a tankless- it gets expensive fast. And unlike power upgrades & tankless heaters, a heat exchanger has a payback in avoided utility costs (probably significant operating cost savings, given the amount of hot water you'd end up using with every shower if the side sprays get much duty-cycle.)

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
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    While the heat recovery systems work, they would not work on many first floor installations unless you had a full-depth basement...you need vertical drop, and if your drain is likely close to the crawl space or in a house with no basement...no go.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the trades Dana's Avatar
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    Quote Originally Posted by jadnashua View Post
    While the heat recovery systems work, they would not work on many first floor installations unless you had a full-depth basement...you need vertical drop, and if your drain is likely close to the crawl space or in a house with no basement...no go.

    ...and that's a fact.

    Even shortys can work in some crawl spaces, but the shortest these days from GFX or PowerPipe are 36". Retherm makes some 3 & 4-inch 30" models though. Your best bet is if you have a full story and an easily accessible plumbing chase or open basement.

    Having a tight proximity of the drain to the water heater counts too or it can become a real PITA (and less effective) with longer plumbing runs between them. But with the right layout it can be pretty easy. In my own home the shower is on the first floor. The low-ceiling basement made installing a 60" version impossible without digging a pit in the slab, but slipping in a 48"x 4-incher had few issues. Since I'd had to move the shower drain to accommodate side-venting a new boiler, getting the boiler/indirect/drain-heat-recovery all nice and tight was dead-easy, so including the heat exchanger at the time of the boiler installation became a no-brainer. Clearly YMMV.

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