water heater

Plumbing

Expansion Tanks & Why They're Important

If your home’s utilizes a boiler and radiators for heating, expansion tanks are an important factor. Hydronic heating produces energy-efficient home comfort as water heated by the boiler circulates through radiators in each room. However, one specific fact of physics presents an issue: Water expands when heated. As the water volume inside a closed hydronic system increases with heat, the mounting pressure has nowhere to go and could potentially trigger pressure relief valves, over-stress system components, and degrade reliability. That’s where expansion tanks come in to relieve that pressure.

Here’s how an expansion tank protects your heating system:

  • Connected to the water line between the boiler and radiators, the tank is divided into two segments: an upper half that receives water expanding under heat and an empty lower half that contains only pressurized air. A flexible rubber diaphragm separates the two halves of the tank.

  • When the system cycles on and the boiler is heating, water volume in the system expands. The resultant pressure increase pushes water into the top half of the expansion tank. The flexible rubber diaphragm expands downward to accommodate this influx and moderating pressure in the system, preventing actuation of relief valves and/or damage to components.

  • When the system turns off, water cools and system water volume decreases. Air pressure in the lower portion of the expansion tank pushes against the rubber diaphragm to expel water out of the upper portion and back into the system. This ensures that system water volume always remains in the safe range, without admitting air into the system.

Here’s a quick way to check expansion tank functioin. While the system’s running, feel the upper part of the tank. It should feel noticeably warm to the touch. The lower portion, however, should feel like room temperature. If both the upper and lower portions of the tank feel warm, contact a qualified HVAC service provider to check the condition of the internal diaphragm and make necessary repair or replacement.

For more information about the installation and maintenance of expansion tanks, contact the professionals at Air Assurance.