# Navien tankless waterheater exhaust pipe freezing



## ben's plumbing (Oct 6, 2011)

robo11 said:


> Can someone give me advice on why or how to fix my Navien tankless waterheater/Boiler, my exhaust pipe that exits threw the roof, keeps freezing up in the winter? I not only use my Navien waterheater for domestic hot water, but I also use it to heat my infloor heating system. I know when the warm air from the waterheater meets the cold outside air it causes condensation that then freezes, but theres got to be a way to fix this, otherwise if I were to go on vacation this time of the year and my exhaust pipe froze up again, it would kick the waterheater out like it did on me last night and hours later if I were not here could cause my inside waterlines to freeze and burst. My house was built just 3 years ago and this has been an ongoing problem each year, I can't believe Navien doesn't have a fix for this, but I actually just got off the phone from speaking with them and they do not have a fix for me. Does anyone else have this problem with their Navien or other boiler/waterheater, and if so how did you fix the freezing up of the exhaust pipe? It only freezes where the exhaust air exits the pipe on the roof, you will see an icicle forming on the pipe just days before its about to kick the boiler out. And to thaw the ice my plumber told me to take the front off the boiler to let the warm house air go thru the unit, and this does thaw it out, but I shouldn't have to take the front off the unit thru out the winter. Theres got to be a fix for this, does anyone have any ideas? Thanks.


 call the installing contractor . something is wrong...pictures will help us help you:yes:


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## md2lgyk (Jan 6, 2009)

I'm not a pro and have not seen a lot of tankless installations, but none of those I've seen, not even one, exhausted through the roof. Mine exhausts through a side wall, with a slight downward slope so any condensation that may form will simply drain out before freezing.


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## SPS-1 (Oct 21, 2008)

Can you give us a little more detail on what its looks like when its frozen? Do you have a 3" ball of ice in the pipe? (would not take a complete blockage to stop the unit anyways, if the exit is partially blocked it will sense the excessive pressure and shut down)

Do you have a (too) fine bird screen on the exhaust? That would accumulate condensation and ice build-up.

Photo of termination of the exhaust pipe would help.


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## Ghostmaker (Mar 2, 2013)

Navien recommends whenever possible, that its water heaters be used as direct vent (or sealed combustion) units which draw all of their required combustion air directly from outside the building and where the combustion air supply is connected directly to the air intake collar of the water heater. •
 If, in the room in which the unit is to installed, there is a continuous and sufficient supplyof combustion and ventilation air in accordance with all local codes, the Navien units may then communicate with that indoor air and a direct outdoor supply is not required.*This non-direct vent method of venting is *
*not recommended for residential installations in areas subject to below freezing air temperatures; 

Above should answer your questions if they did not use outside air for combustion. Outside air during winter is less humid thus will not freeze.
*


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## robot (Jan 17, 2014)

Thanks for the reply's guys. To answer your questions, first, md21gyk-Venting thru the wall was not an option because it would have vented on my front porch and Illinois code does not allow venting thru my soffit. SPS1- the ice didn't seem to be completely blocking my vent, I have a T at the end of my vent and ice forms out both sides, but its enough blockage to shut down the unit. Ghostmaker- my vents are directly vented outside thru my roof and my area is well below freezing during the winter, so the non direct venting is not recommended, although that's exactly what I'm doing when I take the front cover off my unit to thaw the exhaust pipe ice that's formed. Oh, and to the question, did I use a screen over the end of the vent pipes? The plumbing company originally did use the supplied vent grill/screen on the vent pipes, but either the ice forced the one on the exhaust side out or it just kept falling out on its own, and the plumber also only used a single exit fitting on the end of the exhaust pipe, so last year I finally read up on the manual myself and saw where navien recommends a T on the end of the exhaust pipe. So I got on the roof myself and cut off the single exit fitting that the plumber installed and installed a T as the manual shows. I also designed a home made grill/screen out of coated wire that allowed for much larger exit holes on the T. I thought that by adding the T on the exhaust pipe it would take care of all freezing this winter, but it only took about a week of below freezing weather for the ice to form and cause my unit to shut off.
Still needing advice on a fix if anybody else has dealt with this same problem, thanks.


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## Ghostmaker (Mar 2, 2013)

Your Navian needs combustion air from the outside. It cannot be from the inside of the house.

Do you have a pipe from the outside that feeds all the air for the navian to burn when it fires. We are not talking exhaust we are talking combustion air.

I hope this makes it clear.


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## robot (Jan 17, 2014)

Ghostmaker, to answer your question, yes. The combustion air comes from outside, both my exhaust and combustion air vents are thru my roof and one to two feet apart from each other. I know that its not good to leave the front cover off my unit because of a possible hazard like if my heat exchanger ever cracked I could get carbon monoxide in the house, so I don't take it off unless my exhaust vent pipe freezes up. Still looking for a way to keep my exhaust vent pipe from forming ice at the end of pipe.


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## mikegp (Jul 17, 2011)

If you were to put a different shape on the top of the exhaust would it help? Like an upside down J or a T? I have no experience in that, but just wondering if it would avoid freezing with another configuration.


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## robot (Jan 17, 2014)

Mikegp, my plumber originally put the single exhaust(upside down J) that you described in place, but it seemed to freeze up quick in just a couple of nights where the temp got below freezing. Then last year I read the manual myself and saw where to company showed the T on the exhaust end, so that's when I cut off the upside down J and installed the T. The T seemed to help, it took approx. one week of below freezing temps for it to freeze up verses just a couple of nights with the upside down J. Thanks for the thought though.


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## SPS-1 (Oct 21, 2008)

SPS-1 said:


> Can you give us a little more detail on what its looks like when its frozen?


 The only time I have seen a restricted exhaust, it was the screen that was frosted over.


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## Ghostmaker (Mar 2, 2013)

robo11 said:


> Ghostmaker, to answer your question, yes. The combustion air comes from outside, both my exhaust and combustion air vents are thru my roof and one to two feet apart from each other. I know that its not good to leave the front cover off my unit because of a possible hazard like if my heat exchanger ever cracked I could get carbon monoxide in the house, so I don't take it off unless my exhaust vent pipe freezes up. Still looking for a way to keep my exhaust vent pipe from forming ice at the end of pipe.



Thank you for the answer.

Now I'm wondering if the exhaust being so close to the intake may be a source of the issue.

What size pipe did they use for your exhaust vent? A 2 inch vent can only go 24 foot and have 2 90 degree bends.


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## robot (Jan 17, 2014)

Both pipes are 3".


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## beenthere (Oct 11, 2008)

Remove the screens from the exhaust pipe. Screens cause quicker freeze up. Is the tee vertical, or horizontal.


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## robot (Jan 17, 2014)

The T is horizontal, but I installed a forty five degree fitting on both ends. The screen you mentioned is not really a screen at all, what I did was to take coated wire and made a grid on the ends of the forty five degree fittings. I did make the grid openings much larger than the grid that Navien supplied, I made the grid squares just large enough so that birds could not nest in the pipe. The grid did not freeze up completely and block off the pipe, it did form an icicle that partially blocked both exits of the T which was enough to cause the unit to recognize it and kick itself off.


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## beenthere (Oct 11, 2008)

Get rid of the 45s. Make it a vertical tee. Get rid of the wire. It just makes it freeze easier. The wire is just something for the moisture to collect and freeze to.


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