Thread: Tankless Gas Venting

This tankless water heater has a quick turn and streight outside. See pictures. The builder is trying to tell me that the 5 foot above the collar rule does not apply to tankless. AND there HAS to be a rule not allowing this to happen (see picture!) Can someone help me out with IRC or UMC codes on these two issues?

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Originally Posted by K Robertson

This tankless water heater has a quick turn and streight outside. See pictures. The builder is trying to tell me that the 5 foot above the collar rule does not apply to tank-less. AND there HAS to be a rule not allowing this to happen (see picture!) Can someone help me out with IRC or UMC codes on these two issues?

I would start with the manufacture venting instructions.

Originally Posted by Scott Murdock

I would start with the manufacture venting instructions.

Correct.

And short of them you would need to meet the code, which has a minimum 5 feet rise and that cap is not an approved cap for a Type B gas vent - it would need to be a proper cap and terminate vertically - unless the installation instructions covered an installation which was tested, listed, and labeled differently.

Additionally, the vents have a maximum horizontal offset of 75% to 100% of the vertical height, which means that 5 feet horizontal offset needs a minimum of 5 feet vertical height, possibly even almost 7 feet vertical height.

That water heater is also in a "confined space" (or so it looks) and that confined space needs combustion make up air.

Installed as shown in your photo, the discharge from the a/c condenser unit mostly likely will restrict, reduce, or stop drafting dead in its tracks.

If I had the model # of the heater you have pictured I could be of more help. It looks like a Noritz.

If you have a look at this page of Noritz web site it will show you the hood type cap is what they have for through the wall termination. Noritz - Venting - Supplier of Tankless Gas Hot Water Heaters
Also Noritz does not use B vent, it is Stainless Steel Category III vent piping.

Tankless WHs typically use Cat IV AL29-4C stainless steel venting, which is listed for positive vent pressure. Tankless, in general, do not vent by atmospheric pressure but rather mechanically, meaning positive vent pressure. Therefore, B-vent or single walled vent connector would not be appropriate.

You cross-check the listed instructions of the appliance and venting against the code and follow the more restrictive requirements.

Good point about MUA JP. At a typical 176mbh and some as high as 250 for residential applications, that's a lot of air required--about 1,100 -1,700 square feet if you have 8' ceilings.

Also, these babies need a lot of gas. Undersized gas lines can cause reduced firing rate, whistling in the gas lines esp. with CSST, sooting and similar problems with all the other gas appliances in the home including dropping out pilots.

Bob

Location was in the corner of a 2 car garage, so I think it probably has plenty of combustion air. I did not know that these had possitive vent pressure. Think I need a Kaplan course on these. This is only the 1st time I've come across one, but have a feeling it won't be the last.

So even with mechanical vent pressure, the location of the vent hood is still a bad idea, right?

Originally Posted by K Robertson

Location was in the corner of a 2 car garage, so I think it probably has plenty of combustion air. I did not know that these had possitive vent pressure. Think I need a Kaplan course on these. This is only the 1st time I've come across one, but have a feeling it won't be the last.

So even with mechanical vent pressure, the location of the vent hood is still a bad idea, right?

The vent hood location might be OK, it depends on the unit. Depending on the BTU's the manufacturer will have distance requirements. To me it looks like it is about a foot too close to the frieze board and soffit area.

Here is the PDF page 9 with the manufacture clearances for that heater. One problem with the install is the manufacture wants a slight slope downward towards the wall termination so if any condensate builds up in the pipe it will run outside and not back in the heater. If this can not be done then a condensate tee should be installed a vertical or horizontal one depending on the clearances needed.

Originally Posted by K Robertson

Location was in the corner of a 2 car garage, so I think it probably has plenty of combustion air. I did not know that these had possitive vent pressure. Think I need a Kaplan course on these. This is only the 1st time I've come across one, but have a feeling it won't be the last.

So even with mechanical vent pressure, the location of the vent hood is still a bad idea, right?

Contact Noritz, Takagi, and Rinnai, they offer installation classes all the time. Just need to find the dates, and where to be.

I installed a Takagi TK1 in my home about 8 years ago. It's a direct vent unit that terminates out sidewall. It has Category III stainless steel pipe with sealed connections. Install guide says minimum 24" vertical rise off unit. If you know what brand and model it is try looking it up online.

Noritz recommends the rise to be 1 foot but is not required. But they do say to avoid installing the elbow directly to the flue. Here is the PDF page about length and sloping of the vent pipe.

Originally Posted by Trent Tarter

I installed a Takagi TK1 in my home about 8 years ago. It's a direct vent unit that terminates out sidewall. It has Category III stainless steel pipe with sealed connections. Install guide says minimum 24" vertical rise off unit. If you know what brand and model it is try looking it up online.