Specifications

Safety

Thermal Expansion

Water expands as it is heated. For example, 30 gallons of

water expands to 30 ½ gallons as it is heated from 40°F to

120°F. Water cannot be compressed, so it will cause

pressure to build up in the tank if no expansion area is

provided.

In older water systems, expanding water ows from the

heater back into the supply line prevenng pressure build

up. But due to new code restricons, many areas now

require a check valve between the residence and the

incoming municipal water supply. The check valve blocks

the ow of water back into the supply line causing

pressure to build up. This is called a closed water system.

A weeping T&P valve or faucets that drip intermiently

indicate a closed water system.

The T&P valve is designed to be an emergency safety valve

only and should not be used as an operang pressure

relief valve in a closed water system.

In a gas water heater, excessive pressures can

cause the

ue tocollapse creang a potenally hazardous

condion. In both gas and electric models, excessive

pressures will eventually cause the tank to fail.

The best soluon for closed water systems is the

installaon of an expansion tank. Expansion tanks are

designed to absorb expanding water and relieve pressure

on the water heater tank.

The expansion tank has a rubber bladder with one side of

the tank containing air. The air pressure in the tank should

be equal to the incoming cold water pressure.

As the water is heated and expands, it is forced back into

the expansion tank, compressing the air.

As hot water is used, the compressed air pushes the

expanded water out of the tank. This process repeats as

water is heated and used.