Due to the nature of a tankless hot water heater only heating water when it needs to (as opposed to having hot water on reserve), does a tankless water heater still work in a manifold system?

Specifically the PEX Manifolds that take an inlet of city water, an outlet of cold water to water heater, and a hot return from water heater.

I am not sure if water flow for hot is stopped when no outlet is requiring it in a home-run system, or if continuous heating would happen.

enter image description here

1 Answer 1


Yes, it still works. Unless a faucet or fixture is open, there is no water leaving the manifold. The heater is thus not running. When a faucet is in use, water flows through the manifold, causing water to flow through the heater and be heated.

A similar thing occurs with a tank heater. When no fixtures are on, the tank is full of water and it is heated. When a faucet is in use, water from the tank flows through the manifold to the faucet, and that water is replaced by cold water from the manifold. At some point, the thermostat turns on the heater in the tank.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.