CSLB C-46 Solar ContractorElectrical and Plumbing CodesMedium
A solar contractor is installing a new solar water heating system. The system's expansion tank is designed to absorb thermal expansion of the potable water. According to the Uniform Plumbing Code (UPC) and California Plumbing Code (CPC), where should the expansion tank typically be installed in relation to the water heater?
- AAt the highest point in the solar thermal loop for air purging.
- BBetween the main shutoff valve and the water heater's cold water inlet.
- COn the discharge side of the T&P relief valve.
- DOn the hot water outlet piping, downstream of the water heater.
Show answer & explanationAnswer & explanation
Correct answer: B. Between the main shutoff valve and the water heater's cold water inlet.
According to UPC/CPC, an expansion tank for a potable water heater (including solar water heaters) must be installed on the cold water supply line to the water heater, between the main shutoff valve (or check valve) and the water heater's cold water inlet. This placement allows it to effectively absorb the pressure fluctuations from the thermal expansion of water as it heats up, protecting the system.
Why the other options are wrong
- A. This location is for air purgers or vents in a closed-loop solar thermal system, not for a potable water expansion tank.
- C. Installing an expansion tank on the discharge side of a T&P valve is incorrect and could interfere with its safety function.
- D. Placing it on the hot water outlet is less effective for absorbing cold water inlet pressure fluctuations and is not standard practice.
Expansion Tank Placement (Solar Water Heater)
The correct installation location for an expansion tank in a potable solar water heating system, as mandated by plumbing codes, to manage thermal expansion.
- Installed on the cold water inlet side.
- Between shutoff valve/check valve and water heater.
- Absorbs thermal expansion of potable water.
Memory trick: Expansion tank: cold side it must be, between the valve and the heater, you see!