View Full Version : Tempering valve selection

12-27-2009, 09:18 AM
I have a WM Gold Oil boiler that provides forced hot water baseboard heat and DHW.
Recently, we removed an eletric HW heater that was in series with the output from the boiler tankless coil that was being used as a storage tank only - it was not wired to an AC source.
The HW heater would temper the hot water, and now that it is no longer connected, I need to install a tempering valve to help keep the hot water output temperature more consistent during burner cycles.
(I plan on having an indirect or reverse indirect water heater installed in a year or two when we are doing some other renovations)

The most common tempering valve I have seen referenced seems to be the Watts 70A. The data sheet clearly shows the proper installation - a check valve and an adjusting valve on the cold side, and a PRV as well. That all makes sense. The data sheet shows typical installations for both a HWH and a tankless in a boiler.

Then I also came accross the Watts 1170, which sounds from the description that it is a slightly better product:
"This series features a "double throttling" design which combines the control of the hot and cold water to provide a sensitive response to changes in water temperature passing through the mixing chamber."

The installation instructions for the 1170 do not show installation with a tankless coil in a boiler, it only shows a standard hot water heater and radiant heat applications.
I assume it would be the same as installing a 70A, except that the 1170 has built-in check valves. I'd still install a PRV on the cold side, but not a check valve since it is integrated into the tempering valve.

Do the pros have a preference as to which valve is better in this application?

Thanks for your help.

Peter Griffin
12-27-2009, 09:26 AM
I like the Watts valve and both Honeywell and Sparco make a really fine product also.

12-27-2009, 12:55 PM
i've been using honeywell sparco series mixing valves with built in check give them a look.. the honeywell valve will be alot simpler to install than the 70a in my opinon.. No heat trapping required , built in check, comes with union connections easy service...

12-29-2009, 11:20 AM
Thank you for your replies Plumbworker and Peter.
I really appreciate your help.

01-22-2010, 07:21 PM
Ok, two more questions regarding this project:

1.) The tankless coil appears to have been plumbed in backward: i.e. the clearly labled "out" fitting is connected to the cold water suply and the clearly labeled "in" fitting is supplying the DHW.
Since I am going to be changing the piping to the tankless anyway, is there any harm in reversing this so that they are connected properly? I assume the "In" and "Out" are labeled specifically because there is an advantage to connecting it that way. I think I remember reading somewhere on this board that the tankless heats the water slightly more efficiently when it is connected as designed.

2.) The boiler fill is connected to the hot water side of the tankless. It is indeed connected to the same side of the tankless as the "In" fitting, which would normally be the cold water feed, but since the "In" and "Out" are plumbed backward, it is the hot water that feeds the boiler makeup water. I have heard that adding a lot of cold water to a hot boiler can damage it (thermal shock), but is there an advantage to having the DHW feed the boiler, or can I simply connect the cold to the boiler fill?

Thanks again for all the great advice offered here.