When water heats up, it expands a little. In most homes, that extra volume can go back toward the municipal supply. In others, the system is “closed” — and that's when an expansion tank becomes useful, and sometimes required.
What it does
The expansion tank (a small white vessel on the cold inlet) absorbs the pressure from thermal expansion. Without it on a closed system, the relief valve may drip more often and fittings work harder.
The 3 cases where the code requires it
Under Quebec plumbing code, thermal-expansion protection is required if any of these is on your water supply:
- A check valve
- A backflow preventer
- A pressure-reducing valve
Clues it may come up
- The relief valve drips regularly with no leak elsewhere
- You already know there's a PRV or check valve near the meter
- A recent upgrade closed the system (municipal work, etc.)
What we do at Chauffe-eau SOS
During install or a visit, we look at the system type. If the tank is required, we add it clearly to the quote. If not, we don't push it. You can also see where it sits on our compliant-install diagram in the help center.
Questions? 514 387-1434 — plain-language answers.