Courtesy Plumbing

Why Does the Shower Temperature Change When the Toilet Is Flushed?

We’ve all been there, right? In the middle of washing our hair minding our own business singing our favorite go-to shower tune when all of a sudden we are brought back to reality with a sudden jolt of hot or icy cold water. For a few seconds, you are in fight or flight mode as the sheer shock of the drastically different water temperature courses down your back. This is a common plumbing problem we wish to shed a little light on.

The desired temperature of the water is achieved by mixing both cold and warm water together. One of the most common configurations for plumbing pipes is called a trunk and branch system. One large pipe (the trunk) running the span of the house with smaller pipes (the branches) branching off to supply each room or fixture. When one branch is utilized there is less water available to the rest of the branches. So if you flush the toilette (which only needs cold water) there is less cold water available to mix with the hot water and so you will see a rise in temperature in the shower.

Solutions

#1 Install a new mixing valve

You can install a new mixing valve in the shower to help better control the fluctuations of water temperature. Thermostatic mixing valves automatically mix the amount of hot and cold water, so in the event that the toilet flushes, the thermostatic mixing valve will balance the amount of hot water so the water temperature stays even. Installing new mixing valves is probably an easier solution for this plumbing problem.

#2 Reduce the Amount of Water Supply for the Toilet

You can close the supply valve to the toilet to reduce the amount of water that flows when the toilet is being flushed. This will lead to longer fill time but will help alleviate water temperature variances in the shower. There could be a couple of side effects with this method: increased fill times, noise, and less water to remove solid waste. If you are concerned about the amount of water your toilet uses with each flush you may want to consider switching to a new low flow model.

#3 Increase Water Supply

If you find yourself using a lot more water in a particular area you may want to consider increasing the water supply by installing larger pipes. By installing a larger trunk pipe, or larger branch pipe you can supply more water to areas that utilize the most water.

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