Protection during freeze for Rinnai tankless

by Duncan
(San Antonio, Tx, USA)

I have exterior mounted Rinnai tankless water heater. What is the recommended protection for the unit during sustained freezes? I have the lines wrapped but should I cover the unit with a large thick blanket?

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Jun 09, 2015
Rinnai freeze protection
by: Bob Ives

When in doubt I install two solenoid valves. one normally open on the cold water supply and one normally closed on the hot water outlet. If power is lost the valves will drain the heater automatically. This could be connected to a thermostat through a relay to shut off and drain the heater if the outside temperature inside the unit casing gets too low.

Dec 16, 2011
How to protect Rinnai water heater from freezing
by: Anonymous

Your Rinnai water heater is protected as long as the outside temperature doesn't drop below -4 F or -20 C. If you have bad wind-chills as we have in Michigan, your Rinnai tankless unit, even with the internal freeze protection will be affected even with the temperatures slightly above these ones.

Every Rinnai tankless water heater is equipped with the freeze protection feature that includes the electric heating elements. As long as the unit is connected to the power, you water heater is protected.

Rinnai water heater is tankless, but it doesn't mean that it is empty. It has some water inside the internal piping and the heat exchanger, so any loss of power (even if not using for some time) will disable its ability to protect from freezing.

Tip: If the freeze protection system doesn't work for some reason, make that there is some water flow from the water heater (minimum will work).


It is a good thing that you had protected the outside pipes, but the freeze protection system protects the inner components only.

Also I didn't see anyone recommending some sort of the blanket, such as on the tank-type water heaters, so I would do it here as well.

Your Rinnai water heater needs proper venting and correct air supply, so any obstruction might be dangerous.

If you are planning to go on a vacation, and if water heater is not going to be used for some time here is what you should do:

- Shut off the water and gas supply to the water heater.

- Turn the temperature controller OFF.

- Disconnect the power to the water heater.

- Open the drain plug and drain all the water from water heater.

And if any damage occurs on the internal components due to freezing, the warranty is not valid.

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