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Thread: Water Heater for Kohler 12.5 gpm DTVII and SOK 142 gal tub

  1. #1

    Question Water Heater for Kohler 12.5 gpm DTVII and SOK 142 gal tub

    Firstly, I would like to thank everyone in this forum for all of the great advice.

    I am upgrading my bathroom with a Kohler 12.5 gpm DTV II system and a Kohler SOK tub with a fill capacity of 142 gal (Kohler recommends a hot water supply of 70%).

    I considered tankless but it appears that they have more cons than pros i.e. pressure issues, demand, rise, etc (by the way im in NJ). If I am wrong about this please correct me.

    My plumber recommended a 100 gal hw heater which should be fine for the tub but my biggest concern is the shower. The 100 gal will only allow for a 7 - 8 min shower at best. The house has 4.5 baths including the basement bath and standard kitchen stuff. Only 2 of these bathrooms get any real use.

    Can anyone give me an alternative option? I.e. 100 gal tank with, dedicated tankless for the Kohler tub and shower. 2 X 75 gal tanks or a tankless setup that would actually work.

    I also want the water heater to be efficent. Sounds kind of silly if your adding a 12.5 gpm shower system. It's my wife not me.

    Any suggestions are greatly appreciated. If you need more information let me know. I will check back this afternoon.

  2. #2
    Illinois Licensed Plumber SewerRatz's Avatar
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    Well tankless can work for you but you would have to install at least two units. A single Noritz 931 can provide 6 gpm at a 70º temperature rise. With a 50º incoming water temperature that would give you 120º water. So if you pair up the 931 with another unit you can get 12 gpm with the 70º temperature rise. Now most people do not shower at a full 120º it will be mixed with some cold water so this would meet your need, as long as no one starts the washing machine while you are showering. If you want the ability to take the shower, run the wash and a couple other things at once then you can add a 3rd Noritz 931 to the system. Now whats the down fall? Cost! These units retail for $2100 each, then there is gas piping to take in account 3 units running full force will draw 750,000 btuh.

    I would look into the Bradford White GX-1-TW-55S6BN This 55 gallon unit can provide you with 200 gallons of hot waster in the first hour of delivery. It recovers 84 GPH with a 90º rise. Here is the PDF spec sheet on the system. I have seen many homes with your type of demand with a pair of these units plumbed in parallel and where very happy. http://www.bradfordwhite.com/images/...eets/119-B.pdf

  3. #3

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    I would recommend the same water heater as SewerRatz - the Bradford White GX-1-TW-55S6BN.

  4. #4

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    Thanks for responding so quickly.

    My cousin works for a local plumbing supply house and he told me that he can do both the Noritz 931 and Bradford White units for nearly the same price. The Nortiz is about $85 more per unit. Either way it's a great deal on either unit.

    I forgot to mention that this new bath will be PEX. I don't know if that make a difference in this situation.

    My home has a 3" or 4" gas line so it should be able to output a good amount of btuh.

    Would the Noritz save me more money monthly over the BW or is the savings a non factor?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    I don't remember you indicating where you live...that can make a difference. Those tankless units are generally rated at a fixed temperature rise (nominally 70-degrees). Normally, in the summer it isn't a problem. Where I live, I've measured my incoming water temperature at 33-degrees. Bump that up 70-degrees, and then run it down the pipe, and you won't like it. A tank is impacted too, but because it can take time to generate that tank's full volume up to your set point, you can get that temp out of it, regardless of the incoming temp. First hour ratings are a useful thing to look at on a tank, but it depends also on your use pattern. If you have a very high flow rate, you don't get the advantage of that hour to heat the incoming water much, cool off what's left, and you likely won't get that full amount if you try to draw it in 10-minutes verses a continuous, lower flow rate for the hour. That's why you need a bigger tank, or start with the water hotter. Where I live, you are required by code to install a tempering valve on the output of the tank to keep the outlet temperature to a safe level. This also makes the tank 'act' larger, since the flow is mixed with some cold as it leaves the tank (similar to what happens at the tub/shower with your temp control but only on the hot supply). A hotter tank will have more standby losses, though, so insulation is important.
    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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    Default Help-Boiler & Hot Water Tank for Kohler’s DTVII system 12.5 gp & 115 gal tub

    Hi,

    I live in NYC and I have the same exact problem – I am also looking for a boiler and a Water Heater that can handle Kohler’s DTVII system 12.5 gpm and an Aquatic 115 gal tub, along with my washing machine, dishwasher and if my other bathroom is being used. It will also be used to for the loops for the radiant heat for appx. 1000 sq feet.

    My architect has on my plans a Weil-McLain Boiler with a separate 100 gallon hot water tank but my plumber, who is not really doing a good job is recommending a unit called “LAARS”-it’s the Mini-Combo id Residential Space/Water Heater 125,000 BTU per hour. Please see link for specs.

    I’ve asked around about this unit but no other plumber seems to know about it. Everyone I spoke to is telling me to stick to what I have on my blueprints.

    I take long showers and love hot water and I do not want to have any storage. Can someone please advice and help me. I would appreciate any help I can get right now. Has anyone ever heard of the LAARS and how does it compare to a Weil-McLain?

    Thank you all so much!

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    125K btu/hr is nowhere near enough heat to produce that much hot water on demand, especially in an area where the incoming water can get quite cold.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    DIY Senior Member Runs with bison's Avatar
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    Wow, that's about 10 times as much hot water as I use to shower. With that sort of arrangement the shower would be a bigger gas user than even the furnace in the coldest part of winter.

    This large of a use would seem an IDEAL candidate for a drain heat recovery system in the shower. This might cut your burner heat load in half or so.

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