I have 2 (potential) clients with the same problem:
The domestic hot water is either too cold (water in the pipes, no biggy) but eventually warms up to screaming hot. Both have the same setup: oil-fired boiler with the DHW heated there in sort of a ‘storage tank’ compartment in the boiler.
I can’t believe there’s no thermostatic control to the water temp. My system delivers constant temp because there’s a separate tank which is an extra ‘zone’ on my system.
Were their systems setup wrong? If not, is there a thermostatically controlled mixing valve available to add cold water to the too hot water yielding something less annoying and dangerous?
ThanX
Egon
Replies
My tank heated by the boiler is off to the side, separate. It has a thermostat which calls the boiler for heat.
There are tempering valves available for point of use or at the main HW source.
A good plumber or plumbing supply should be able to explain and supply all the above.
You can also add if accessible a passive loop to send the heat in the pipe back down to the HW tank. Additionally, you can add a powered pump that will keep the same HW temp in the line by circulation.
Remodeling Contractor just outside the Glass City.
Quittin' Time
Calvin - Yes, my system is setup this way so it amazes me they are having these problems.
Dave - I'll go and see if there is a backflow preventer and study other details. We have some REAL good plumbing houses here and I'll see what they recommend as far as a tempering valve.
I just KNEW they had to make such a thing - thanks!
Yes. And yes.
There should be a thermostatically controller pump or zone valve for the water tank so, like any other zone, it can call for heat and stop heating when hot enough.
It could be going over temp because there is not back-flow preventor (either a check valve or a zone valve). The DHW may get hot enough and stop asking for heat. Yet another zone getting heat with cause a slight delta P across the Hx in the DHW tank and eventually getting it too hot.
There are "tempering valves" / "mixing valves" that let you control the output temperature with a dial. Different models have different ranges, like 80-140F or 100-180F, etc. For DHW you want to cover the range of 110-130F at a minimum. Taco (about $80) and Watts (about $60) both make them. I like the Taco a bit better, it is flanged and the handle is easier to turn. Home Depot, etc have them although the guys in the orange vests rarely know that or kow where they are located. Usually in the locked display cage in plumbing with the zone valves. Or go to a real plumbing supply house.
".... same setup: oil-fired boiler with the DHW heated there in sort of a 'storage tank' compartment in the boiler."
Some boilers have DHW taps in lieu of an indirect water heater. Weil-McLain, WTGO oil fired boilers have this feature. Some of those boilers have very simple controls because they are designed for comfort heating and modulation is typically done with control valves. If the systems that you describe are as I suspect, the tempering valves that DT mentioned are the simplest and least expensive way to go. If, like the W-Ms that have this as an add-on optional feature, have buitl-in controls that shoudl be adjustable to maintain normal DHW (110 - 140) temps. Indirect water heaters have adjustable thermostats, very similar to a stand-alone tank type water heater.
Have a plumber or heating guy set up the storage tank with a mixing valve that is on the out pipe from the storage tank that will be going to the fixtures, showers, etc. Also make sure you have a vacuum breaker on the out side of the tank too. The best mixing valve I've seen is a honeywell, I think it runs about $100. You can get them in 3/4" or 1/2" and probably 1", etc. It is a brass valve painted silver and looks like a cross. One side is the hot feed, the other side the cold feed and the mix out side then the other is a large gray knob with a blue and read swirl on it that shows the + and - for the adjustment. All you do is turn it like a spicket and that changes the mix. After it is installed then you go to each shower valve and set the water temp, my code is 110 for showers, 120 for faucets.
Without a mixing valve the water will be boiler temp water, most boilers in this area are set for 160 to 180. That would cook you very quickly. Check out your local plumbing/heating supply house. See what they have but everyone I know uses the honeywell on customers and their own.