Selecting a max output temp for a WH tempering valve?

[houndzilla]

Watts has two options:

80-120 degrees max 12 gpm (advertised as a domestic water tempering valve) http://www.watts.com/pages/_products_details.asp?pid=6842

90-160 degress max 25 gpm (I think this is for boilers and other types of hot water systems) http://www.watts.com/pages/_products_details.asp?pid=6841

Is being able to heat shock the hot water plumbing (kill biofilm and legionella) a worthwhile capability to have? I'm sure the question is overthought, just curious though.

Additionally, 12 gpm seems to be more than sufficient for all the fixtures that could be pulling hot water at the same time. Piping is copper.

 

[Smooky]

For domestic hot water you should go with the valve that limits the hot water to 120 degrees. The water heater needs to be hotter than 116 degrees to eliminate legionella in the tank. You may not need a mixing valve if the hot water heater is big enough to handle your maximum flow of hot water. The mixing valve allows a small tank to act like a large tank.

 

[Sponsor]

 

[houndzilla]

For domestic hot water you should go with the valve that limits the hot water to 120 degrees. The water heater needs to be hotter than 116 degrees to eliminate legionella in the tank. You may not need a mixing valve if the hot water heater is big enough to handle your maximum flow of hot water. The mixing valve allows a small tank to act like a large tank.

Tank is over sized (75 gal.) for the fixtures connected, it was sized primarily to accommodate a 100 gal. 2 person tub and have hotwater leftover for things going at the same time.

I want to keep the tank set at 140* and we only have some thermostatic fixtures in the house, I wanted to make sure the non-thermostatic fixtures don't get into scalding range.

Thanks, I'll stick with the 120 degree max tempering valve.

 

[Jadnashua]

12gpm may not be enough depending on what hot water users you want to have running at the same time. The one with the larger range can still be adjusted anywhere within the specified range, so you can set it to 120-degrees (and it probably comes from the factory preset there). Except for limited uses, the maximum in a residence should be 120-degrees for the hot supply. The one with the larger range will give you a little adjustment range to compensate...the one limited to a max of 120 would be just that...at the maximum. As it ages, it may no longer be able to maintain 120-degrees.

 

[houndzilla]

Jim, I'm a spec junky too. Doing some napkin math I've finding that I would have to contrive a situation where each in use tap is turned to full hot and running at the same time. I have the union version and looking at the MFR spec sheets they are the same size, so if need be it would be pretty easy to swap it out if I find that I'm bumping up against the max flow rate.

 

[Jadnashua]

Well, the things don't last forever, either...mine doesn't really work any more, but I've been too lazy to change it out. It could be dangerous, but, at least my shower is a thermostatically controlled valve, and can't get all that hot...the body of the valve does get hot, but you normally only touch the handles, which are insulated from the body. When mine started going, I could adjust it some, but no longer.

Let us know how it works out for you...feedback helps improve the end product here on the forum.