Mixing Valves

Nick C. K.

I am a home inspector - not a heating contractor. I honor your (heating contractor's) knowledge. I come humbly before you to discuss and ask about mixing valves. I was looking at a Weil McLain boiler serving a hot water baseboard system. It co-generated domestic hot water via a coil within the boiler. You understand, cold in - hot out. And between the cold in and the hot out there was a mixing valve. However, it was an ordinary gate valve.
****My questions are these: Is this acceptable? Are ordinary gate (or ball valves for that matter) designed to operate at these higher temperatures? What sort of mixing valve should I see in this situation? Are there automatic mixing valves that monitor the temperature of the outgoing water and conastantly adjust the temperature (like some of the more expensive shower body controls) so the temp remains constant? Do mixing valves at this location have any particular name(s)?
I appreciate anyone's help - and thanks for the time and consideration. - Nick

Mark Eatherton1

By code....

on NEW installations, these devices are supposed to be a self regulating, anti-scald tempering device. The only problem is, that the code doesn't take reality into consideration. When installed in an area with extremely hard water, the calcium comes out of suspension and attaches itself to the moving/working components of the tempering valve and render it useless. Hence, the use of a simple mixing bypass set up. Although not anti scald, the valve configuration you described WILL limit the output temperature of the "system" to something less than what the water temperature would be without it.

In some cases, the boiler/coil were installed long before the code addressed the anti-scald issue.

Brand name wise, Honeywell Sparco, Watts, Leonard,Simmons etc. If you specify a unit in a hard water area, make sure that you provide for removal/flushing and replacement of the valve in the near boiler piping configuration. It is also recommended that the manufacturers near boiler piping diagrams be followed to a T.

As a home inspector, I have a question for you. Do you provide combustion analysis and combustion zone worst case scenario depressurization testing as a part of your services, or just a quick look see?

If you don't test, you'll never know.

ME

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