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Thread: Gas Water heater for bathroom renovation

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  1. #1
    DIY Junior Member tomtbone's Avatar
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    Default Gas Water heater for bathroom renovation

    I am planning a bath renovation a few months down the road and I am pretty sure our 30 gallon water heater aint gonna cut it. Its the shower that has me concernced and I'd like some advice as to the size/recovery rates I should be looking at.

    The shower will have 3 shower heads with one shower head (approx 2.5) and two Kohler body sprays which give out 2 gpm each. So it looks like 6.5 gpm max. I did a flow test with a 5 gallon bucket in the bathtub and got around 8-9 gpm so it seems like I have enough flow.

    This is the only bathroom in the house, so apart from the rare dishwasher/washing machine going at the same time, I just need to compute this for the shower. Can someone help me out?
    Thanks!

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    Retired Defense Industry Engineer jadnashua's Avatar
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    You have to ask yourself how long a typical shower will be, and that may include adding back-to-back shower times. Discounting the WH's ability to reheat water, you can use about 75-80% of the capacity. Now, depending on how hot you set it, your shower doesn't use full hot, so figure out how much actual hot you need. Then, look at recovery rates and first hour capacity. As soon as the WH detects the temp dropping, it will start up the burner, and that will extend it some beyond the 75-80% (which is what gives you the first hour capacity). Tank burner output varies quite a bit, so you can get quite a bit out of a smaller tank if you want. You can work out what you need from that, then try to match it up with a model and brand.
    Jim DeBruycker
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    DIY Junior Member tomtbone's Avatar
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    Thanks!
    So lets say I want to take 2 10 minute showers back to back. That totals 130 gallons. Just for example I am looking at a 50 gallon Kenmore right now that has a recover of 42 gph and a first hour of 90 gallons. Can you help me decipher this a bit to see if this will do the job under normal shower temp and wh temp setting?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Another factor you need to include is how cold the winter cold water is. Say that is near freezing if you live in a really cold climate (or you have a deep well), verses say souther FL, where it might be closer to 60-degrees or even warmer in the winter. That Kenmore wouldn't cut it. The pros here recommend Bradford White or Rheem from a quality viewpoint.

    Say the incoming cold was 50-degrees (a common spec) and you wanted your shower at 110 (may be a little hot). And, say you set the WH temp to 120 (about the minimum you should consider). You'd be using almost all hot, since the 50-degree water would cool it off with only a little cold. If that incoming water is 33-degrees (I've seen that at my house), then even less cold would be required to temper it down to a desired point. That first hour assumes the use is constant, so you'd need probably 120 gallons of hot in 20-minutes. You don't have the extra 40-minutes of adding heat, so it would run out quicker. You can make a WH look bigger if you raise the temperature, but there's a limit on how high you can go and still keep things safe.

    You're asking the WH to provide hot water for 1/3 of an hour, so you need to be able to provide that hot water faster - that means a bigger tank, or a bigger recovery rate. You'd get about 40-gallons from the tank initially, and only have 1/3 of that it could produce during the 20-minutes of recovery verses a full hours rating.

    That tank could provide hot at a flow rate of 1.5gpm for that hour. More initially, but then you'd have to throttle way back, since it can't recover.
    Last edited by jadnashua; 02-11-2010 at 05:09 PM.
    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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    Master Plumber Redwood's Avatar
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    Depending on where you live and the winter water supply temperatures this may be your best bet...
    http://www.noritz.com/homeowners/pro..._water_heater/
    Sometimes you have costs associated with waste...

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    DIY Junior Member tomtbone's Avatar
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    For what its worth, I am getting 42 degree cold water out of the fauces living in Massachusetts.

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    DIY Junior Member tomtbone's Avatar
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    Quote Originally Posted by Redwood View Post
    Depending on where you live and the winter water supply temperatures this may be your best bet...
    http://www.noritz.com/homeowners/pro..._water_heater/
    Sometimes you have costs associated with waste...
    I think I could probably get by with the nr98...... or maybe not now that I'm looking at the temp rise. NR111 minimum
    Last edited by tomtbone; 02-11-2010 at 07:52 PM.

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    Plumber jimbo's Avatar
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    You might get 90 gallons in the first HOUR but in 20 minutes, you get 35 gallons. Not gonna work!

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