Protection during freeze for Rinnai tankless

My inlet line froze up during 11 degree F weather. I has done this once before in 7 years. I got a four pack of flexible foam (like to make seat cushions) and cut it up to line the bottom and sides where the water lines come into the box. Also wrapped more in around the lines. Then overlayed one piece to cover all the pipes and lines. I think this should do the trick. I tested it by running hot shower for 15 minutes, went out and checked - nothing burned or singed. This is all on the bottom of the box, well away from the heater.

Move from Jersey to Round Rock Texas of July 2020 into a newly built home with this system and were unaware of how this system would perform under freezing conditions and I’m so disappointed with this system!! No hot water pressure and the lines are wide open and not a drop of water on the hot water side!! No one informed us on how to or what to do under these conditions!!!

Building Inspector just told us that all exterior water heaters - tankless or not - must be enclosed as per California code. I am afraid of interfering with airflow as it exists. Rinnai doesn’t even make a cover except for pipes but they are saying entire unit needs a cover.

Just got off the phone with a Rinnai installer who said the best way to keep your water lines from freezing was to wrap the pipes and install a pipe cover which if you have a Rinnai, they make. Usually $99 plus installation.

I'm trying to answer that same question. There is not enough clearance inside the box to put any real insulation. Take a look at your Rinnai manual. It says not to obstruct air flow. My Rinnai has a horizontal vent near the top on a front that certainly can't be covered by any exterior homemade insulation framework.

The tag on the side of my Rinnai specifically says it must be mounted outside. It does not say that it can only be used in Miami or placed that don't get cold. We should have been warned of this freezing flaw in the design.
This, it seems to me, is an engineering fault that Rinnai ought to address, with some recommended solution.

Please post any remedies you find at this site, and I will do the same.
Good luck!

KenB
North Carolina

KJ: Many thanks for those options. In fact, on cold nights, I'm using the alarm clock method, and it has worked well so far. Many thanks.

Ken B.
North Carolina

If your system was installed with drain valve(s) on the inlet and outlet as well as isolation (shut off valves) on both sides then you can actually shut off the feed valve (cold) and outlet valve (hot) and then open the drain valves thus allowing the unit to be drained of water.

Once back above freezing or next morning when up and around using water, you can close the drains, open the inlet and outlet and should be able to get flow as long all lines/valves to and from heater have been protected against freeze temp so they can be operated.

Alternately, one could set an alarm every few hours during night, get up and let the water flow long enough to get hot water for a couple minutes thus insuring that the lines will not freeze inside the heater.

Low temps ranging from 1 - 10 F. last two nights, and no hot water. When outside temps reached 25 F. Today used the hair dryer to try to thaw things out. Began getting weak flow with hot water in shower on full. May not be creating enough demand to kick in the heating element.

Will let faucet flow for now and see if it will improve. Will take this and other comments adjacent to my heating guy (this has happened before). This appears to be a design flaw by Rinnai, one that by these comment dates seems to be long-standing. Do other manufacturers have fewer freeze problems? Suppliers and installers need to inform the consumer, and then squeeze Rinnai for a remedy, it seems to me. Class action suit anyone?

Our inlet line is exposed from the elements within the housing cover but it has no insulation to protect from freezing temp, so we woke to no hot water this morning. I'm thinking I could wrap foam insulation around the 3/4" inlet water line but am concerned with the potential for fire risk, as I don't know the proximity of the end of an inlet to the heating element itself. Anyone ever tried this?

Our Rinnai has frozen 2 years in a row. Any new techniques to avoid this. It installed on the outside because our builder seems to think Chesapeake VA does not get cold. We have the heat tape and everything.

Today I awoke to 16 degrees F temperature and water barely trickled from the sink faucet when I turned on the hot. Went outside and the Rinnai was not running. Left the faucet on for 5-10 minutes, the pressure increased slowly and the Rinnai kicked on. Therefore I would say protection to -4 F is exceedingly optimistic. Going to let mine trickle when temps fall below 20 F.

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.

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.