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I am getting ready to install an Eco temp i12 tankless water heater. From what I have heard there is a possibility of cold air backdrafting through the direct vent and into the water heater, thus damaging the heat exchanger and ruining the unit. I plan to run about 10 feet of exhaust vent through my heated basement and then out the wall, will that prevent freezing air reaching the unit, since the cold air would have to travel through a warm pipe before reaching the unit? Does anyone else have experience with a tankless water heater in a cold climate? I live in Michigan. Thanks for any input.

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A quick web search turns up some information. Obviously water heaters mounted outside require special handling. The Rinnai line has two lines of defense against freezing, including ceramic heaters and a mode that will run the combustion periodically to keep the unit warm. Naturally, the water lines still need to be insulated and heated to ensure against freezing.

These protections of course also work for indoor-mounted units. Other brands don't necessarily include these features though. It doesn't look like Eccotemp does.

I haven't bothered to read through their installation manual. However, guidance found on other sites suggest that as long as the air vent is at least 6' long in insulated space, this should be sufficient to prevent freezing from infiltration of outside air. So your 10' run is almost twice as long as you need to accomplish this.

Other things you can do to minimize the risk are:

  • Make sure that the vent openings on the exterior are facing away from prevailing winds.
  • Install a backdraft preventer (flapper) on the exhaust, to further reduce the likelihood of air movements through the vent system while the unit's not operating.

Some useful/informative pages I found include:
https://www.mclayservices.com/blog/cold-outside-will-outdoor-tankless-hot-water-heater-still-work/
https://www.waterheaterleakinginfo.com/cold-weather/
https://propane.com/2018/09/17/eight-cold-climate-tips-for-tankless-water-heaters/
https://www.eccotemp.com/blog/tankless-water-heaters-indoor-vs-outdoor/

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  • No, no, no! Never install outdoor tankless heaters in the snowbelt! Those heat features are for freak freezes like the day Seattle had buses sliding sideways down hills. Or that random frost where I was the only guy in the whole parking lot who owned an ice scraper. Emergency anti-freeze features are NOT for daily use. The "Mclay services" link looks like "content marketing" keyword spew, but even it is talking about draining a heater you are abandoning for the winter e.g you are a snowbird. – Harper - Reinstate Monica Oct 8 '19 at 2:43
  • @Harper: you are welcome to your opinion, but in the case of the Rinnai brand, the manufacturer disagrees with you. I'm fortunate to not have to care myself, but if I had to decide between their opinion and yours, I'd go with the manufacturer every time. rinnai.us/faq/tankless-water-heater/… – Peter Duniho Oct 8 '19 at 2:45
  • Yeah, I'm only going by the links you put in your answer yourself. They all say what I just said there. They are bragging that the unit can stay outside in winters if you drain it. The Rinnai brand has a bunch of asterisks, including an autodrain system they don't provide. Regardless, OP is not installing a Rinnai, and Eccotemp is perfectly clear "no", so this is bad advice. You're from Stack Overflow, which explains your salt; do you honestly believe "I haven't bothered to read the manual" would fly there? – Harper - Reinstate Monica Oct 8 '19 at 3:01
  • @Harper: not sure what bee got in your bonnet, but you'll catch more flies with honey, if you get my drift. The OP's question was about a heater installed indoors; I did not, and still do not, see a need to go into extensive detail regarding the exterior installation of any brand of water heater. If you don't like the answer, please just go ahead and down-vote it. Your rant isn't adding anything here and your complaint is about the straw man you set up, not anything I actually wrote. – Peter Duniho Oct 8 '19 at 3:06
  • The root of the problem is that you ranted off on Rinnai heaters then admitted Eccotemp doesn't have those features. That doesn't make any sense. I am suggesting you clean it up, since indeed my criticism is non-sequitr to your answer, but it's there because of your diversion. – Harper - Reinstate Monica Oct 8 '19 at 3:16

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