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Old 03-30-2020, 08:21 PM   #1
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Changing vent style on tankless heater


Hi All,
Our house has a tankless water heater that hangs on the outside of the house (direct vent) I have created an outdoor shop (just a deck and roof -- our climate is fairly mild) in the same outdoor space, and would like to change the vent type from direct vent to using a vent pipe.

The manufacturer (Noritz) has said that the top parts (vent versus direct vent) are not interchangeable. I'd like to "bolt on" a vent pipe/chimney to direct the exhaust up and out of the shop -- a vertical distance of 7 feet.

One way that I have come up with is to simply attach a rectangular vent vertically to the face of the heater. The current exhaust port/vent is a flat oval that is 8.5 inches long and 1.5 inches tall. I'd seal all seams and curve the bottom to direct the flow upwards. I was thinking that a rectangular vent that is around 10 inches wide by at least 2 inches deep.

Does this sound reasonable/do-able? It would be a huge deal to replace the heater, as it heats the house by radiant floor heat. I also don't have a great other option for the location of the shop.

Thanks,
David
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Old 03-30-2020, 08:23 PM   #2
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Re: Changing vent style on tankless heater


If the manufacturer doesn’t allow it, you’ll have to change the heater.
CO isn’t something to play with.
What’s the model number?
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Old 03-30-2020, 08:41 PM   #3
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Re: Changing vent style on tankless heater


Hi Rough,
Well, that's just... rough! Model number is N-0751M-OD. I am looking for a way to accomplish this without replacing the heater. I have a cO2 detector that is quite accurate and loud, so I feel like I will have that as a way to make sure that my solution is correct.

What I am trying to do is to design the venting system to be of a large enough capacity to work without going completely overboard. Or, if the exhaust is heavy and needs assistance (vent fan), to know that as early as possible...


Thanks,
David
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Old 03-30-2020, 09:22 PM   #4
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Re: Changing vent style on tankless heater


If you have a UL listed CO detector, it’s useless unless it’s an all out venting failure. They don’t alarm until 1 continuous hour at 70 PPM or above.
CO2 is carbon dioxide. Not carbon monoxide.

Quote:
This water heater is for outdoor installation only. Never install it indoors
Manual specifically says don’t do what you want to do.

http://www.noritz.com/u/n_0751m_od_i...ion_manual.pdf

Looks like you’ll have to move this one to a new location or buy a new one that can be vented.
You can’t DIY design a venting system when the manufacturer says specifically not to attempt it.
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Old 03-30-2020, 09:44 PM   #5
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Re: Changing vent style on tankless heater


Quote:
Originally Posted by roughneck View Post
If you have a UL listed CO detector, its useless unless its an all out venting failure. They dont alarm until 1 continuous hour at 70 PPM or above.
CO2 is carbon dioxide. Not carbon monoxide.
In fairness, the ul ones with digital displays start displaying at around 30 ppm and can show down to 11 pushing a peak level button.

But doesn't change the fact that relying even on a low level co alarm to prevent co poising due to unapproved venting is as crazy as relying on a smoke alarm to alert to not to code, dangerous wiring.
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Old 03-30-2020, 09:46 PM   #6
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Re: Changing vent style on tankless heater


Quote:
Originally Posted by user_12345a View Post
In fairness, the ul ones with digital displays start displaying at around 30 ppm and can show down to 11 pushing a peak level button.

But doesn't change the fact that relying even on a low level co alarm to prevent co poising due to unapproved venting is as crazy as relying on a smoke alarm to alert to not to code, dangerous wiring.
This is true, some of the UL listed models are (slowly) getting better. They should have overhauled the requirements years ago but thats a whole topic all to its own.
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Old 03-31-2020, 12:52 AM   #7
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Hi Rough,
Okay, you got me — I wrote cO2 when I should've written CO. I know the difference, and expect that you knew I did as well. The monitor I have reads CO levels from zero on up, and the alarm goes off as soon as CO levels cross into an unsafe amount — not an hour later, as you wrote...

Since I own the heater, I've read the whole manual at least once and some sections several times. Could you please point out the section where it specifically says that I cannot do this? I have found plenty of info regarding how close the device can or cannot be installed to other features (windows, for one), but the only info I have about venting is what I have regarding my initial question is in my first post — that I spoke to a tech at Noritz and that the top section (vents out the top or vents out the front — direct vent) are not interchangeable. None of that came from the manual. Maybe I have missed the section that you referenced. I would appreciate it if you could tell me what it is.

I hear what you are saying about not messing with this stuff, and I will likely move the heater or my shop. I would still like to know the above, because I have not found that info yet.


Thanks,
David
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Old 03-31-2020, 07:59 AM   #8
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Re: Changing vent style on tankless heater


I did, the heater isn’t to be installed indoors. Says specifically within the manual.
Various codes within the NFGC deal with unapproved venting and modification of fuel burning appliances that are not approved or sanctioned by the manufacturer.
The manufacturer said no when you spoke to them, national code says no, the manual says no. Seems like a very clear cut answer.
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Old 03-31-2020, 11:39 AM   #9
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Re: Changing vent style on tankless heater


I think this is the information you are looking for.
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Old 03-31-2020, 01:51 PM   #10
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Re: Changing vent style on tankless heater


I think it is dangerous. You can do whatever you want to do until you get caught or someone finds your body. Do you feel lucky?
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Old 03-31-2020, 01:58 PM   #11
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Re: Changing vent style on tankless heater


Hi KC, All (or any),
Thanks for the reply. I understand what the instructions say. At no point have I suggested that I could have this heater AS IS in an enclosed space. What I have been seeking from the start are suggestions about converting this to a vented setup.

The easy answer is "don't do it". I didn't need to write into a forum for that. What I am looking for it the "here's how to do this, with these expenses, risks, concerns or whatever". It would be easy enough to then weigh the options at that point and start with a different heater or move the shop

I spoke to the technical support team at Noritz again today, and the tech specifically did NOT say that it would not work, but did say that any modification was outside of topics upon which they would provide advice. They also said that the top vented version of the same heater uses a 4 inch vent pipe -- the equivalent of the oval exhaust port on this model. Intake air is provided below the combustion chamber through holes in the outer cover, so that would not provide any conflict, as it could if intake and exhaust were using the same port (back pressure from a vent pipe could be a factor in that case).

I suspect that I could fashion a rectangular plenum that attaches to the exhaust vent and transitions into a 4 inch or larger pipe that goes up and out. I can measure CO levels throughout the day to verify that the setup is indeed safe. Whether it is worth the trouble is still an open question.


Thanks,
David
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Old 03-31-2020, 02:49 PM   #12
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Re: Changing vent style on tankless heater


So you want a DIY forum to violate manufacturers instructions and national code to tell you how to performed non-approved modifications to your exhaust venting, because you have you have a CO detector?
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Old 03-31-2020, 03:03 PM   #13
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Re: Changing vent style on tankless heater


Any alteration you do to the vent configuration, will void the UL listing/approval of that boiler.


You won't get that kind of help here.
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