anti-scald device

[nelaco]

Hello group. I just got a house built in 1966 in Annapolis, Maryland. It has 3 full baths. The one on the second floor I had a single handle Sandard anti-scald valve installed. The 2 other bathrooms on the main floor are still stock so when someone in the house flushes a toilet, or opens a fawcet, the temperature changes a great deal. I have access from the basement to all the pipes that go to these bathrooms. My question is: Should I install a valve at the boiler, that way it takes care of the whole house, or should I do it at each bathroom's pipes. Are there advantages from one method to the other? Would you also please be specific of what type of valve to use? This house has a boiler (uses fuel oil), and no water heater.
Thank you for any help you can give me.

[LazyPup]

A whole house Anti-scald valve will not solve your problem.

For safety reasons the Plumbing Codes limit domestic hot water systems to 140degF maximum and showers to 125degF maximum. In most applications these conditions are met by simply setting the water heater to 125degF.

In some applications the boiler or water heater is also used for hydronic space heating. In this application it is desirable to operate the water heater at 180degF. We must then install a whole house Anti-scald valve to limit the domestic hot water supply to the code maximum of 140degF on the mains. We must then measure the actual temperature at the shower and adjust the whole house anti-scald valve to insure the showers will not go above 125degF. (the mains may be hotter because the 15degF difference is often lost to radiation in the distribution piping before reaching the shower)

When you are showering you have hot water entering one side of the mixer and cold entering the other. You then manually set the mix to get the desired shower temperature. If another fixture on the run is opened, such as flushing a toilet it will cause a momentary change in the line pressures feeding the shower mixer, which results in changing the volume of flow of either the hot or cold. Any change in the volume then results in a dramatic change in your mix ratio at the mixer resulting in a hot or cold shift in temperature.

Previously shower mixers were simply two faucetts combined into one output and the user adjusted the rate of flow from both the hot and cold water supplies.

The codes now require that all showers must be equiped with a mixer valve that has an intergral anti-scald limiter to insure the hot side cannot exceed 125degF.

When it became necessary to design a temperture sensing and limiting system into the shower mixer, many manufacturers than took it to the next logical conclusion and built in a temperture regulating systems rather than just temperature limiting.

While the temperature limiting device can insure the water temp will never go above a preset point, it cannot prevent the temperature from falling below the preset, whereas a temperature controlling mechanism can constantly sense the output temperature and alter the hot or cold input valves to maintain the mix at your desired set point.

In order to insure that you will not get the sudden drops in shower temp when other fixtures are used you would need the temperature regulating type shower mixer, which can sense the actual output temp of your shower water.

[nelaco]

So is it possible to just put a mixer from the basement under each bathroom? or do I need to replace the valves with new ones? Thank you for your excellent explanation.

[LazyPup]

The make an inline type of thermostatic control valve that could be installed on the lines in the basement. My only concern here is that you would want to put it directly on the lines to the shower, otherwise the toilet could still effect the line pressures and consequently the shower temps.

[nelaco]

Yes, exactly, I would just cut the pipes that go right to the showers and install some kind of valve. I just don't know if the make anything like that. Do you know of one...model...make...? Thank you again.