Outdoor Tankless Water Heaters and Rodents

I appreciated the lengthy discussion of tankless water heaters, but it brought up a question. It seems these are sometimes installed outdoors, which I have seen. I noticed that while the problem of insect was discussed, there was no mention of rodents. I recently encountered this situation:

The tankless heater pictured had to be replaced because the mice had chewed up all the wiring inside the unit.
Does anyone have a ideas for what to recommend to sellers/buyers with regard to protecting outdoor units from field mouse nesting?

Was it installed per the manufacturer’s installation instructions?


Get a cat!


My assumption is that it came in through the combustion air intake. It is ok to put a screen on the intake. I would just recommend making it a screen with the largest mesh size possible to prevent rodent entry. You don’t want to use a fine mesh screen that will plug easily.

Recommend them to contact a pest control technician for rodent exclusion programs. Then they’ll learn what to do, what to block, what not to store, etc. Those mice might be getting into other vulnerable areas.


I’m really interested in what kind (manufacturer) it was.

It was a deer mouse.

The water heater was a Richmond. Has the same kind of exhaust slot as other brands, but also slots for air intake on the front cover and underneath. The owner has tried moth balls, steel wool, aluminum foil.

Do you have a farther out view of the actual installed water heater? That can help answer the installation questions.

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I agree with Roy.

Thanks Randy! :grin: