At Local Plumbing, we often get asked whether a water heater expansion tank is necessary. While not every home requires one, for many properties in San Rafael, Mill Valley, Petaluma, and across Marin and Sonoma Counties, this small device can prevent big plumbing problems.
So, what exactly is a water heater expansion tank—and how do you know if your home needs one? Let’s break it down.
A water heater expansion tank, also known as a thermal expansion tank, is a small pressurized tank installed near your water heater. Its job is to absorb excess water pressure created when water heats up and expands. Without an expansion tank, this added volume has nowhere to go, and that pressure can damage your plumbing system—leading to:
Your plumbing system is designed to operate within a safe pressure range. When that pressure spikes repeatedly—especially in closed-loop systems with check valves or pressure regulators—it can wear out your pipes, fittings, and appliances.
An expansion tank acts as a shock absorber. It protects your water heater, pipes, and pressure relief valve by reducing stress on the system and limiting unnecessary water discharge from the relief valve.
Not every home needs one, but many homes in Marin County and Sonoma County do—especially if:
In California, the California Plumbing Code (CPC) mandates the use of expansion tanks in homes with closed systems. Most homes with PRVs or backflow devices fall into this category, meaning excess pressure has no route back into the municipal water supply.
If you’re not sure whether your home needs one, here are some red flags that could indicate pressure-related issues:
Some homes can safely operate without a water heater expansion tank. Here’s when it might not be necessary:
Homeowners sometimes confuse the two, but they serve different functions:
Many homes need both to properly manage pressure and protect plumbing components.
The correct expansion tank size depends on your water heater’s capacity and your home’s water pressure. Here are a few things to consider:
You can use an online expansion tank sizing calculator or call Local Plumbing for a quick evaluation. We’ll help you determine the right size and model to fit your system.
If you're unsure whether your San Rafael or Petaluma home needs an expansion tank—or you're experiencing plumbing issues that could be related to pressure—give us a call.
At Local Plumbing, we provide expert water heater services, code-compliant installations, and professional plumbing inspections throughout Marin and Sonoma Counties. We’ll help you stay up to code, avoid costly damage, and get the most out of your plumbing system.
Call us today to schedule a consultation!
Serving San Rafael, Mill Valley, Novato, Petaluma, and surrounding areas
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Phone: 415-484-0454
Email: Info@localplumbingca.com
Address: 323 Pine St. Suite F., Sausalito, CA 94965
C16&C36 Lic#1091739
Open: Monday-Sunday: 24hrs
Emergency Services Available