Water Heater Combustion Air Question

I did an inspection back in November on a 2007 build. The water heater was replaced in 2014 and was properly permitted by the AHJ. The buyer/buyers agent let the utilities lapse and be shut off between then and last week. The gas company came out to re-install the gas meter and in the process had to check the gas appliances apparently, in doing so he red-tagged the water heater and disconnected its gas supply with the note ‘no-combustion air’. The water heater is installed in a garage that is approximately 24x30, 720sq ft and by my knowledge installed correctly and meeting requirements.

Nothing with the design of the home has changed since 2007 when the home was built or since 2014 when the water heater was replaced and permitted by the AHJ. The gas company says there needs to be a vent cut in the wall to the exterior near the water heater for combustion air. The agent and buyer are trying to get me to pay the estimated $600 for the work to be completed.

I suppose my question is, what are the requirements for combustion air for a water heater in a garage and why would November of 2019 be any different than 2007 when the home was built or March of 2014 when the water heater was replaced then inspected and permitted by the city?

Refer to the SOP

3.0 Plumbing
IV. The inspector is not required to:
R. Evaluate or determine the adequacy of combustion air.


Thanks… :man_shrugging:

Was there just a water heater, what kind was it? how many BTU? was it behind a door in a closet? Which SOP do you follow? do you ever comment about combustion in your reports? have you ever called it out before? if you have, it could be argued that you cannot use SOP that limits you and does not require you to determine proper air combustion.

Just a water heater, RHEEM 40 gallon, furnace is inside the home. 38,000btu, not behind a door in a closet. Follow NACHI SOP. I only comment on combustion air if it’s blatantly obvious that it is insufficient or is drawing from a living/sleeping space.

I would talk to the gas company, a supervisor. Ask them if an appliance is allowed to draw combustion air from inside and go from there. Perhaps they sent a new guy who didn’t know better… unless something is missing, 24x30 open space garage should be plenty for 38k BTU WH.

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That is for sure, Simon. :smile:

Thanks. I’ve talked to both the city and the utility at this point and have conflicting answers. The city says it is fine the way it is and the utility says it ‘cannot draw air from an interior space’. I guess they are counting the garage as an interior space.

Very frustrating :joy:

William nailed it. I’m glad nobody threw codes around like they know this jurisdiction :blush:

If you really want to calculate adequate combustion air, here’s how, but as so many have pointed out, it’s way beyond our SOP and not always simple. Disclaim it and tell why.
I’ve commented on it if it was obvious, or when the water heater was in a basement obviously set up for later finishing in a manner that might reduce combustion air, like in a corner near plumbing connections that make it obvious that installing a bathroom (or other room) might isolate the water heater and reduce it’s available combustion air.

It is very possible that the Gas Company may have standards that supersede the Local Jurisdiction (AHJ) to protect them.

And that reason is simple: people can and will sue a gas company for millions if someone is killed or injured… People can’t (usually) sue The City Code Inspector AHJ.

Natural gas came into our area in about 1985 and for many years the Gas Company did their own inspection on top of the AHJ inspections. Mainly because the Gas Company did not want the inexperienced AHJs killing people. For those years all garages that had gas appliances installed had vents both high and low and if they didn’t they would be Red Tagged and would not hook up gas service regardless of what Local Code Inspectors said.
Now since the local 'code boys are doi’n the inspect’in. And should be up to speed. I find problems all the time even in newer homes with lack of combustion air, and I’m not talking in garages, but small closets. (In my area you do not need a permit or a licenced plumber to replace a water heater) When I see these questionable installs, I do the calculations and call it out.


The problem is the AHJ enforces the mechanical code and the gas company enforces the fuel gas code. There are many conflicts between the two codes. Prior to becoming a home inspector I was a state building inspector and had these conflicts too many times. The end result would be that we would call the supervisor of the gas company and they would usually see it our way and concede.

Hi Kenton,

In your first example in the link you provided I believe there is a typo. In the calculation is says square feet instead of cubic feet:

x 50 sq. ft.

7,500 cubic feet of room air needed for proper combustion

Thanks for catching that and letting me know David, I’m correcting that page now!

Thanks everyone. 3 Licensed plumbers looked at the situation and basically said the gas utility is out of their mind. Problem solved.

Well done the plumbers are probably your final authority. You live in New Mexico make sure that the plumbers are not just license for plumbing but are license for gas as well. Their license will be indicated with a JPG.

A plumbing license in New Mexico has absolutely nothing to do with gas piping, flue venting or combustible air calculations.

So what now, did the gas utility turn the gas on? and what’s with not allowing to draw air from inside? is this one of their requirements or a mistake someone made? any competent utility is supposed to have this in writing as part of their guidelines to avoid having disputes like the one you ran into.

How’s this for a narrative on disclaiming identification of adequate combustion air for gas-burning appliances?

"Accurate identification of adequate combustion air for gas-burning appliances requires research and performing calculations that exceed the scope of the general home inspection. Any comments included in this report regarding combustion air are suggestive only. Accurate identification of adequate combustion air for gas-burning appliances should be made by a qualified contractor. "

Nice narrative, Kenton. :smile:

Thanks Larry. Kinda repetitive, but short and makes the point pretty clearly, I think.