Can I Feed Four Toilets on One Mixing Valve?

Purpose of a Mixing Valve

• Also called a "tempering valve," this plumbing gadget is designed to add a mix of hot and cold water to control the temperature of the water in the line. These are important enough to often be required by building codes. For toilets, the mixing valve adds a bit of hot water to the cold water in the line. If the water sitting in the toilet tank is colder than the air outside of the tank, condensation -- or "sweating" -- forms on the outside of the tank. This can drip and damage the flooring or rust the surrounding pipes.

Where to Find It

• The mixing valve should be along the cold water line leading to an individual toilet, but in close proximity to a hot water line that would feed a shower or sink. The lines need to be close together to allow the mixing valve -- which can be Y- or T-shaped -- to attach to both. If the mixing valve has been placed to feed numerous toilets, it may be above the hot water heater. Occasionally, it can be found inside a wall where it is difficult to reach; this indicates poor planning or plumbing work, and the valve should be relocated for future repairs or replacement.

Need for Individual Valves

• While many homes now have a main mixing valve near the hot water heater to prevent scalding injuries for showers and sinks, each toilet in the home should have its own mixing valve made specifically for mixing water for the toilet. Numerous toilets on one mixing valve located away from the toilets can overload the mechanism, causing it to malfunction or wear out quickly. Indications that the valve is malfunctioning are hot water in the toilet or condensation on the tank. Because of the complexity of adding a valve in the proper location, an experienced plumber should handle the installation.

Other Fixes

• If a mixing valve handling a large number of toilets seems to be working for all but one toilet, the homeowner has several other options to prevent condensation. A mixing valve can be placed on the cold and hot water lines leading to that toilet; a decorative toilet tank cover could be placed over the tank to prevent water from dripping on the floor; a tank insulation kit may be purchased and installed to cover the inside of the tank and control condensation on the outside; or an aquarium heater can be placed inside the tank to raise the temperature of the water.