In homes that utilize a boiler and radiators to produce hydronic heat, expansion tanks are a vital component to ensure system reliability and safety. Hydronic heating has kept homes comfortable in winter for more than 100 years now by circulating water heated by the boiler through radiators to maintain consistent temperatures throughout the house.
Because water volume expands when it’s heated, however, excess pressure could develop inside the system and trigger pressure-relief valves and/or damage other components, too. That’s where expansion tanks play a critical role to prevent excess pressure. Here’s how a typical hydronic system makes use of this simple safety component to maintain system performance and energy efficiency:
- Installed in the main water line that extends from the boiler to room radiators, an expansion tank consists of two chambers separated by a flexible rubber diaphragm. As water volume in the system expands when heated, water is pushed out of the main line and into the empty upper chamber of the expansion tank to relieve excess pressure.
- As water continues to flow into the tank, the rubber diaphragm flexes downward to expand the capacity of the upper chamber and continuously relieve pressure on system components.
- When the boiler cycles off, water cools and system volume decreases. Air pressure in the lower tank chamber pushing upward against the rubber diaphragm slowly impels water out of the tank and back into the main water line. Water volume is thus safely maintained at both cool and hot temperatures without allowing air to enter the system.
Over the years, the rubber diaphragm in an expansion tank may deteriorate, allowing water to fill both chambers. You can perform a quick test to check tank condition. When the system’s running, feel the side of the tank. The upper portion should feel warm and the lower portion should be at cool room temperature. If the entire tank feels warm—or you note other signs like pressure relief valves opening—the tank is likely defective. Contact your HVAC contractor for qualified professional service.
For more about maintaining expansion tanks in your heating system, contact the professionals at Beyer Boys.