# Way to block cold air from coming down hot water heater exhaust?



## PorkChopsMmm (Aug 16, 2010)

I installed a small tankless propane water heater in our kitchen in the fall. It has a short distance to an exterior wall, about 24", before exiting via a stainless steel exhaust that was included in the kit. The exhaust also has a built in "damper" of sort to close off wind flow when no hot water is running. One night when it was -20 degrees outside the water heater froze and started leaking. I got another unit to replace this one and placed a 90 degree elbow and a "T" fitting on the end to block and wind from entering the exhaust. It didn't seem to matter as this Sunday night it was -25 and the new hot water heater froze.

Is there anything I can do to "block" the cold from coming back to the water heater in only 24" of space? Our house is heated to around 60 degrees whenever this happens. I would like to avoid electric solutions as we live off grid with solar. I just don't know much about running exhausts for these and can't find much info on the web. Thanks!


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## simi-steading (Sep 27, 2012)

You got a lot bigger problem than you know.. the real issue is the fact carbon monoxide is probably not being vented, and is seeping into your house.

Your vent is probably no where near long enough or high enough. It could be too that it doesn't have any rise in the horizontal run of the flu.. 

You need to find a way to get it up above your roof line with a longer flu to help it vent property.. If it comes straight off the top of the heater and runs horizontal into the wall, then only up a very short distance, this too can be why


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## simi-steading (Sep 27, 2012)

I just did a fast search for you and found this site.. Hopefully it will help explain what your problem is, and how to fix it.. 

http://www.structuretech1.com/category/water-heater-backdrafting/


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## PorkChopsMmm (Aug 16, 2010)

This is a direct vent model that is made to vent horizontally. I read that site you sent over earlier -- I don't think it applies to my type of unit. When it is running the exhaust gas is exiting fine. The unit is freezing overnight when it is not it use. It does not have a pilot so no gas is being used, or vented poorly, when it is freezing. It seems to be just cold air entering in through the as-designed horizontal exhaust.










EDIT: It also does have a backflow preventer built in, FYI.


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## simi-steading (Sep 27, 2012)

Huh.. wow.. I have a hard time believing that is meant to vent properly without any rise on the flu and being below the roof line..


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## PorkChopsMmm (Aug 16, 2010)

New tankless water heaters are mainly all like this now. After checking multiple manufacturers I think I followed everything correctly. The advice is for the exhaust run to be horizontal and to be as short as possible.

Assuming everything is up to snuff, how do people deal with cold temps when they affect the exhaust of units like this? Even with a roof exhaust cold air sinks, so wouldn't you have the same problem of a potential freeze?


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## simi-steading (Sep 27, 2012)

When you have a longer flu run, the warm air rising keeps the cold air from settling.. BUT, you don't have a pilot either that keeps even a small warm air rise..

I know too with some, a well sealed house can cause problems back drafting.. 

Sorry, I'm not up on the new heaters.. I originally thought you were talking about a regular every day tank heater.


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## farminghandyman (Mar 4, 2005)

at one time there were "Automatic Flue Dampers", I do not know if there still avaible or not or even still allowed, , they would shut the flue down when not being used and open with flame was detected, 

do your own web search,


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## Harry Chickpea (Dec 19, 2008)

I would call this a design flaw. If you installed according to manufacturer instructions and it froze, _*it ain't your problem, it is theirs.*_ I would be on their heinies to figure out a solution, and I would be sure to let them know that if they didn't replace the unit and fix the problem I would be notifying enough of the proper people that they would be forced to stop selling. 

I am more than a bit puzzled why a tankless heater wouldn't fire on automatically if the water in it got to a freezing temperature - even if there was no draw. A fifty cent thermostat could probably do the job.


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## PorkChopsMmm (Aug 16, 2010)

Thanks for the advice. This is the 3rd unit I have gone through. This time they want me to mail it back on my dime and I will be without a water heater the whole time. I would rather fix and move on.


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## Harry Chickpea (Dec 19, 2008)

I looked at their instructions:

http://www.eztankless.com/resources/articles/natural-draft-tankless-water-heater-installation-tips/

You are installing counter to their warnings.


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## sammyd (Mar 11, 2007)

Tankless heaters start when they detect water flow not temp so they won't start even when the temp is freezing.
There usually isn't much "sink" to fire the thing with no flow, it could heat up pretty quick and that could cause a whole different set of problems.


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## PorkChopsMmm (Aug 16, 2010)

Harry Chickpea said:


> I looked at their instructions:
> 
> http://www.eztankless.com/resources/articles/natural-draft-tankless-water-heater-installation-tips/
> 
> You are installing counter to their warnings.


You are mistaken. From their instructions:

_NOTE: This page and the information on this page does not apply to any EZTANKLESS brand tankless heater that is direct vent (connects to A/C 110V power supply)._

My unit does use AC power and as previously mentioned is direct vent.


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## Harry Chickpea (Dec 19, 2008)

OK, thought you might have one of the cheaper models. As I said initially, it appears to be a design flaw. I saw mention of other tankless units that used a small electric heater to resolve the issue, but you don't want to do that.

The problem you now run into is that any alternative "fix" is potentially unsafe and certainly not covered by code, which means insurance wouldn't pay if it caught fire.

Manually, you could have an insulated outside cover that would REQUIRE the gas to the unit be valved off before it could be placed in position. Or... you could place a lamp under the unit in a way that the heat from it would heat it.

Really though, the design flaw is that the pilotless ignition would be better if there was a sensor that reverted it to a pilot light operation when the water reached a low of about 38 degrees and cut the circuit out at about 60 degrees. It would be a simple circuit, but again if you made it, it would put you in a legal no-mans land.


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## Gray Wolf (Jan 25, 2013)

We have a tankless propane hot water heater in our off-grid house that vents up about 5' in the pantry before it goes in the unheated attic. We had freezing problems when it got below "0" until we started leaving the pantry door open to allow the house heat into the pantry and allow the warmth to leak up the stack. I initially ran the vent stack up to the ridge so sliding snow didn't rip it off but distance alone wasn't enough. We heat with wood so it's usually plenty warm inside the house and pantry.

Can you add pipe to go up? It's not cheap but ..... Room heat will get into the exhaust pipe and rise and hopefully counteract the cold comming down.


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## Harry Chickpea (Dec 19, 2008)

His unit brings in outside air through a pipe that contains the flue pipe. Heat on the unit might help, but since it is "sealed" to the outside, warm air won't leak up the stack.


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## fordy (Sep 13, 2003)

PorkChopsMmm said:


> New tankless water heaters are mainly all like this now. After checking multiple manufacturers I think I followed everything correctly. The advice is for the exhaust run to be horizontal and to be as short as possible.
> 
> Assuming everything is up to snuff, how do people deal with cold temps when they affect the exhaust of units like this? Even with a roof exhaust cold air sinks, so wouldn't you have the same problem of a potential freeze?


 ................Why don't you build a shroud for the exterior portion of the exhaust and install one of those flapper dryer vents that open up when the airflow starts ? , fordy


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## PorkChopsMmm (Aug 16, 2010)

Fordy, I think I will need to do something similar. A flap type vent to try and block out the wind/cold. I installed the new unit last night and it was -10. I took off the exhaust piping and left it off the unit all night, which is not easy to do without disassembling some of my surrounding cabinetry. I put my hand in front of the exhaust inlet and could feel very cold air -- hopefully a flap vent will stop the cold air from penetrating so easily.


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## Guest (Mar 6, 2014)

fordy said:


> ................Why don't you build a shroud for the exterior portion of the exhaust and install one of those flapper dryer vents that open up when the airflow starts ? , fordy


I'm just jumping in here out of the clear blue but I would think you'd have to have a power vent to blow something like that open . I know very little about direct venting a tankless heater & haven't bothered goggling the subject .
It was stated the vent had a back-flow preventer & I would think that is what's supposed to stop cold air from coming back in the vent . I wonder if the back-flow preventer could be malfunctioning . The OP seems to understand how it's supposed to vent so I would assume that has already been checked .
A manually operated flapper would keep the heater from venting properly unless one remembered to open it every time hot water was used . Not a good solution in my opinion but sometimes one must do what one must do .


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## PorkChopsMmm (Aug 16, 2010)

Thanks WV. Similar to how a gas clothes dryer vent works, I am hoping that this flap would work out as well. This tankless heater does use a powered fan to blow out the exhaust so I would just have to make sure the flap isn't too heavy. 

The back-flow preventer is working but it is all the way at top of the water heater, allowing cold air in, when I think it would be better suited on the exterior of the house.


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## Guest (Mar 6, 2014)

PorkChopsMmm said:


> Thanks WV. Similar to how a gas clothes dryer vent works, I am hoping that this flap would work out as well. This tankless heater does use a powered fan to blow out the exhaust so I would just have to make sure the flap isn't too heavy.
> 
> The back-flow preventer is working but it is all the way at top of the water heater, allowing cold air in, when I think it would be better suited on the exterior of the house.


Ah OK , I didn't think it had a fan to blow the air out the vent . Sounds like a flapper would work if as you said the fan would blow the flapper open . A person would still need to check the flapper occasionally to make sure it didn't get bound up & stop working .


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## Harry Chickpea (Dec 19, 2008)

"................Why don't you build a shroud for the exterior portion of the exhaust and install one of those flapper dryer vents that open up when the airflow starts ? , fordy "

If the input air and output air are concentric pipes, encasing the openings and using a dryer flapper vent would be *insanely* dangerous. Worst case scenario: The moment combustion started, there would be the possibility of negative pressure. That would seal the flapper closed, create a low oxygen situation and then a flow of propane into the enclosure, re-ignition, and explosion and fire. The design would be similar to a WWII buzz bomb.


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## Guest (Mar 6, 2014)

Who suggested encasing the openings ? I must have missed that .


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## fordy (Sep 13, 2003)

WV Hillbilly said:


> Who suggested encasing the openings ? I must have missed that .


 
.................I did , and I never encourage buzz bombs for use in heating water ! But , Harry is much more perceptive than I at cause and effect so he has picked up on a major problem with the dryer vent . , fordy


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## Harry Chickpea (Dec 19, 2008)

I just have weird connections in my mind that make some things obvious to me, while I am oblivious to other things. Besides, buzz bombs are a neat design.


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## Guest (Mar 6, 2014)

I can see that I'm going to have to be less trifling & goggle the venting of these heaters so I'll have a better understanding of how it all is designed to function . Obviously the supplied back-flow preventer isn't performing it's intended function if that function is for preventing cold air from coming back in the vent pipe .
At this point I am assuming that the vent is a double walled type pipe in a pipe with an air space between the two pipes .
I am also assuming that the heater gets combustion air from between the pipes & vents out the inside pipe . I have been busy between posting so haven't dedicated any time to thinking about this or researching this . 
I just looked at the picture posted by the OP & it appears as though the combustion air enters through the dark slots in the pipe & vents out the white looking holes nearer the end of the pipe .
This seems to be an ongoing problem & may be a design flaw . I say this only if that back-flow preventer isn't malfunctioning in some way .
About anything one does to modify the system in any way is going to void the warranty but if it isn't a simple problem with a relatively simple solution & is indeed a design flaw I think I know what I would do . 
I really haven't troubleshot this idea in my mind yet so it could be unworkable but here goes & feel welcome to shoot it down .
The heater has a blower motor for the vent that runs when the heater is heating . I would install a thermostat that is controlled by outdoor temperature & wire it into the blower motor circuit wiring so that when it got really cold outside this thermostat would cause power to be provided to the blower motor & the motor would run . After the outdoor temperature raised to the desired temperature the thermostat would break the circuit & stop providing power to the blower motor & the motor would stop running . 
This may sound complicated to some but really is a very simple little wiring job .
I also believe this could be done so that nobody could ever tell it had been done if removed & therefore wouldn't void the warranty .

On second thought I will say that I know for a fact that I can make that blower motor run controlled by a thermostat & if the motor running & blowing air out will solve the problem the premise of what I wrote is solid . In a power outage this won't work . I still welcome being shot down . I just reread your post & that you're off grid so the power outage wouldn't apply unless you ran out of your own power .

PS I know that you said you wanted to avoid an electrical solution but I would imagine that motor is small & doesn't use much electric . Also by controlling it with a thermostat it would only run when using water & when very cold outside .


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## Gray Wolf (Jan 25, 2013)

Solutions that don't use electricity would be best for off-grid use.

The idea with this type of system is that it doesn't use inside air for combustion. While the piping could be modified to use inside air and only exhaust outside, it would defeat the design. Your call.

Heaters like ours only use the piping for exhaust and are probably better for off-grid.

I see no good way to put a flapper style damper on the one you have and doubt that you want to have some sort of manually opperated one you'd have to engage in order to get hot water.

Have you contacted the manufacturer to see if they have a fix?


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## PorkChopsMmm (Aug 16, 2010)

Just as an FYI, this unit pulls air from within the structure -- not from outside through the venting pipe. The only function of the pipe is for exhausting air. Air from your house is sucked in for combustion.

I contacted the manufacturer when the first freeze happened and they weren't much help -- although my goal was getting a warranty repair. I will call them back to see if they have any pointers. 

I may have missed it, but if internal air is used for combustion, just like on my propane gas clothes dryer, and the dryer has a flap on the exhaust -- why couldn't this have a flap also on the exhaust? Not trying to start a fight -- just trying to understand. Thanks!


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## idahodave (Jan 20, 2005)

I wonder why there's a back flow. 

Seems like warm air should rise in the stack. 

Do you have other appliances that use inside air for combustion (furnace, gas water heater, woodburning, or exhaust fans)? 

Is the exhaust on the windward side of the house?


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## PorkChopsMmm (Aug 16, 2010)

It is strange, but there is hardly any stack. Just 24" of metal pipe going out horizontally. We *do* heat with a wood stove -- so maybe it is drawing air in throw the opening? Although when we open the windows a crack the fire does not change... leading me to believe our house isn't that airtight. This is on a side of the house that receives wind but a 90 degree bend, a length of pipe, and a T at the end was added to try and stop any wind -- didn't seem to help.

Hopefully a flap vent will stop the chill.


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## Guest (Mar 7, 2014)

PorkChopsMmm said:


> It is strange, but there is hardly any stack. Just 24" of metal pipe going out horizontally. We *do* heat with a wood stove -- so maybe it is drawing air in throw the opening? Although when we open the windows a crack the fire does not change... leading me to believe our house isn't that airtight. This is on a side of the house that receives wind but a 90 degree bend, a length of pipe, and a T at the end was added to try and stop any wind -- didn't seem to help.
> 
> Hopefully a flap vent will stop the chill.


Once again I & others was incorrectly assuming combustion air was coming from outside . I'll go back to thinking a flapper might work but won't make any more assumptions . I do think the back-flow preventer is malfunctioning or defective in design because it obviously isn't preventing back-flow . 
Would you mind providing the brand name & model number of the heater ? One more question , was this vent system designed to work with this heater or is it a more generic kit designed to supposedly work with various heaters ?


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## farminghandyman (Mar 4, 2005)

Harry Chickpea said:


> I would call this a design flaw. If you installed according to manufacturer instructions and it froze, _*it ain't your problem, it is theirs.*_ I would be on their heinies to figure out a solution, and I would be sure to let them know that if they didn't replace the unit and fix the problem I would be notifying enough of the proper people that they would be forced to stop selling.
> 
> I am more than a bit puzzled why a tankless heater wouldn't fire on automatically if the water in it got to a freezing temperature - even if there was no draw. A fifty cent thermostat could probably do the job.


 they do not keep the water hot, they only heat it when it is flowing as there is a flow sensor, and it has to be more than a few drips or small stream so if you have a leaking faucet it is not kicking on, 

NO FLOW NO HEAT. flow then thermostat, and it is more of a limit (at least the one I am aware of).


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## Harry Chickpea (Dec 19, 2008)

I understand that that appears to be the way they are made. I also understand that people often design for limited design parameters so they can make their crud more inexpensive. If a product is sold without those parameters being clearly stated at the outset, it is fraud, stupidity, or cheap. The UCC roughly states that a product has to be suitable for the use it is sold for or the contract is void because the "good faith" has been breached. IMO, this is a case where the OP could go to a decent class action lawyer and prevail. The company asking him to return the product on his own dime after it is clear the design doesn't work is... I'd rather not say, but it ain't nice. The longer they ignore the problem, the greater the liability they have.

Very seriously, if I were general manager of that business - heads would be rolling, there would be a "Not for use in climates with below zero temperatures" immediately plastered on all advertising and brochures, and a new crew brought in to add what I mentioned before - a pilot heater to keep the system from freezing. I'd then release a NEW product with another $100 added to the price, for sale to people living in those climates. That would more than cover product modification costs.

Incompetent product design and cheaping out frosts me, especially since all it takes is a little field testing to get feedback on what does and doesn't work. My first software had a couple of issues. I corrected them, and as other issues came up - even though they were related to the operating system instead of my product - I over-designed until they were no longer a problem. Why? Because they DESERVE better. Because it is what is SPOZED to be done. Because I'm lazy and don't want customers interrupting my watching a movie.


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