Frequently Asked Thermal Expansion Tank Questions
What is Thermal Expansion? Thermal expansion refers to the charac- teristic of water to expand when heated. Unlike air, which can be compressed, Thermal water grows in volume and must be accommodated.
Expansion How do I Deal with the Thermal Expan- sion Problem? Thermal Expansion Valve Cause for Concern? Thermal expansion can be solved by installing an expansion tank or valve to your system near your water heater. The tank or valve will alleviate the pressure building in the heating tank. The expan- sion tank is inexpensive and requires no drains in addition to conserving water. Expansion valves are another option but require more complex plumbing solu- Still not convinced that you may need a thermal tions for draining water. expansion device?
Go to your favorite web browser and put in Isn’t a Temperature and Pressure Relief “thermal expansion,” there are plenty of videos (T&P) Valve Enough to Deal with Thermal Expansion? of exploding water heaters. No. A T&P valve is not a thermal expan- sion device because the constant drip- ping of water from the valve can result in a mineral deposit that can create a blockage, causing the T&P valve to be- Water Quality Section come ineffective. Plumbing codes re- 35 Stony Point Road quire thermal expansion be properly Santa Rosa, CA 95401 addressed. Phone: 707-543-3965 Fax: 707-543-3937 Website: srcity.org/993/Water-Quality Thermal Expansion Can Cause Hot Water Heaters to Explode!
Thermal Expansion Danger Open System Figure A
Most homes are supplied with hot water A typical hot water heater in an “open” sys- from a natural gas or electric heated tank tem has only a temperature and pressure type water heater. Usually water heaters (T&P) valve to prevent a rupture of the hot are taken for granted until they quit oper- water heater (figure A). Open systems allow ating and a cold shower alerts you to a expanding hot water to push into the cold problem. Unfortunately, a water heater water line. that is not maintained can become a safety hazard. Closed System Water expands as the temperature rises. The extra volume caused by thermal ex- Once a private water system in a typical Figure B pansion usually expands into the cold home has a pressure reducing valve or back- water line in an open system. If you have flow device installed, it becomes a “closed” a pressure reducing valve or a backflow system and needs a thermal expansion de- device, your household water system may vice. The most common thermal expansion become a “closed” system. A closed sys- device is an expansion tank (figure B). The tem just means there is no place for the tank is partially filled with air which is com- hot water to expand. pressible. This compressibility allows the ex- panding hot water a place to go. These ex- The thermostat of the water heater nor- pansion tanks can be orientated in any direc- mally maintains the water temperature at tion and are placed on the cold water line. about 130º F (54º C). However, if the thermostat fails to shut off the heater, the temperature of the water will Different Types of Thermal Expansion Figure C continue to increase. Devices
If the water temperature increases to In addition to thermal expansion tanks, there more than 212º F (100º C), the water are tankless thermal expansion devices within the tank becomes “superheated.” available. These valves relieve the expanding When this superheated water is suddenly water pressure by discharging the water to exposed to the atmosphere when a atmosphere (figure C). Since a drain line is faucet is opened, it instantly flashes into required on the thermal expansion valve, it steam and a violent reaction may result. needs to be plumbed to a drain line with an In fact, the tank may explode! air gap for safe disposal.