But why? What effect does a toilet have on your shower? Are your pipes or your water heater to blame?

Here’s why a flushing toilet changes your shower’s temperature – and a few ways that you can help prevent it:

Why do I feel the burn?

One of the most common plumbing set-ups is known as the trunk and branch system, which features one large-diameter pipe running the length of the building (the trunk), with smaller pipes diverting off, like branches from a tree, to individual rooms or fixtures.

With this set up, when one branch demands water, there is necessarily less water available for the other branches. This is dramatically illustrated by a flushing toilet and running shower: When the toilet flushes, it uses only cold water, which means there is less cold water available to mix with the piping hot water in your shower. When loss cold water mixes in with the hot, your shower feels warmer

What can I do?

Though it may seem like the most obvious solution, your water heater isn’t to blame. Instead, the issue is with demand and supply – your system is demanding too much cold water at once, leaving you with only a scalding supply. To prevent uncomfortable showers, you must either reduce demand, increase supply, or ensure that your plumbing can compensate for any shifts. 

Here are a few ideas…

Change Your Mixing Valve

Consider installing a new mixing valve in your shower to help prevent rapid changes in temperature. Modern thermostatic mixing valves automatically balance the amount of hot and cold water being mixed, helping prevent drastic rises in temperature before they happen. So if the cold water supply is reduced by a flushing toilet, the amount of hot water is adjusted automatically, keeping your temperature consistent.

Increase the Amount of Water Available

The good news? Increasing the amount of water available to your system can help resolve the issue. The bad news? Doing so will most likely mean making major changes to your plumbing system, like increasing the diameters of your trunk pipe or your branch pipes.

Install a Manifold to Distribute Water More Evenly

An even more drastic – but effective – solution would involve installing a manifold with home runs into your system.  With this set-up, a dedicated pipe is run between each fixture in your house and central load-balancing manifold. This would require major renovations to your system, but it would ensure an even balance of hot and cold water to both your toilet and shower.

For all of your plumbing hassles and mysteries, don’t hesitate to drop Combat Plumbing a line! Our experienced team is here, day and night, to help keep your system at its very best.