Thread: combustion air pipe

For those of you more familiar with the IRC ... can you direct me to the proper section? This is a suburban inspection.
Gas water tank and gas dryer in closet, closet is part of 1/2 bath. Instead of cutting louvers in the walls or doors for combustion air from the home, they ran a 4" pipe from the closet out to the attached garage. Garage of course is enclosed. Don't think the 4" is large enough for the roughly 60K BTU. Can't imagine running it into the closed garage is legit. The garage has one 6" through wall vent at the opposite corner. I don't think that will suffice either. I would like to recommend running the combustion air pipe to the exterior. Looking for some backup because I'm guessing it will be a fight.
Any suggestions appreciated.
Thanks, Markus

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Originally Posted by Markus Keller

For those of you more familiar with the IRC ... can you direct me to the proper section? This is a suburban inspection.
Gas water tank and gas dryer in closet, closet is part of 1/2 bath. Instead of cutting louvers in the walls or doors for combustion air from the home, they ran a 4" pipe from the closet out to the attached garage. Garage of course is enclosed. Don't think the 4" is large enough for the roughly 60K BTU. Can't imagine running it into the closed garage is legit. The garage has one 6" through wall vent at the opposite corner. I don't think that will suffice either. I would like to recommend running the combustion air pipe to the exterior. Looking for some backup because I'm guessing it will be a fight.
Any suggestions appreciated.
Thanks, Markus

Mr. Keller: Section 2407.

Thanks, i'll pull out the book and find the info.

You also have issues with make up air as well as combustion air for gas clothes dryer, and why not allowed in bathrooms (or their closets) generally lacking both sufficient make-up air in addition to the combustion air.

Thanks HG. I also added in ...
- possible negative flue pressure when bath xfan is on
- compromised firewall separation to garage
- lack of fire damper in pipe run to garage
- hazards of the pipe acting as a conduit into the home for fire, smoke or fumes

Regardless of the amount of air intake, the firewall is breached. Even if the air intake passes through the garage to the outside, a single wall pipe without drywall protection is a problem also.

Ed Massart

I believe you both meant to say "separation" not "firewall". The required separation wall, fireblocking and draft stopping, and related provisions for and restrictions of penetrations thereof.

Fuel Gas Code adopted by the municipality. Be it NFGC or IFGC. Dryer Manufacturer Instructions. Gas Dryers require sufficient Make-up Air in addition to "combustion air". Electric clothes dryers require Make Up air as well.

I suspect the combustion air was barely calculated for the water heater, and operation of dryer behind closed door compromises both appliances.

Perhaps I assumed this half-bath containing laundry and fuel-fired water heater "closet" abutting separation wall to garage was an interior one (no window). However window or not, if mechanical ventillation or mechaical exhaust (fan in half bath) is present will compromise required air for persons , as will the activities of the dryer exhaust, even when run without use of combustion (air only mode).Negative pressure when clothes dryer is on, even in air-only mode.

One wonders where and how the clothes dryer is exhausting.

Originally Posted by Ed Massart

Regardless of the amount of air intake, the firewall is breached.

Originally Posted by H.G. Watson, Sr.

I believe you both meant to say "separation" not "firewall".

Thank you, H. G., that is something I am consistently pointing out and reminding everyone here - the wall between the garage and the house is a "separation" wall and not a fire wall, thus completely different ... and less stringent ... requirements apply.

Yes it is a separation wall, not a firewall. The dryer does have a dedicated 4" pipe run to the exterior. However the pipe run is about 39' with multiple elbows. This of course exceeds the IRC 25' rule.
There is no window in the bathroom. No louvers on the bifold door to the closet, no louvers in the door or wall to the rest of the house.
I put the negative pressure issue and other other items mentioned by others in the report. Did a follow-up call with the client yesterday, client doesn't have any questions.
I spoke with the Muni vent inspector who at first didn't have any issue with the install until I brought up the potential problems. Then he did the back peddle dance and thought it should be changed. I just called to verify what Code they were under.

Markus,
Heck with the municipal/city inspector. You need to go by what Nicor, People's Energy, or North Shore Gas will require. They're the ones who lock off the meter if it's not right regardless of what ANYONE else says. When it comes to gas appliances the gas companies are God.

Originally Posted by Markus Keller

However the pipe run is about 39' with multiple elbows. This of course exceeds the IRC 25' rule.

To me, they should go ahead and take that rule out, or give it some teeth - they took all the teeth out of that rule by the exception without making the exception fully controlling.

(I have added the missing part in bold and underlined text)
- M1502.6 Duct length.The maximum length of a clothes dryer exhaust duct shall not exceed 25 feet (7620 mm) from the dryer location to the wall or roof termination. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.8 rad) bend and 5 feet (1524 mm) for each 90-degree (1.6 rad) bend. The maximum length of the exhaust duct does not include the transition duct.
- - Exceptions:
- - - 1. Where the make and model of the clothes dryer to be installed is known and the manufacturer’s installation instructions for the dryer are provided to the building official, the maximum length of the exhaust duct, including any transition duct, shall be permitted to be in accordance with the dryer manufacturer’s installation instructions, and where the effective length of the exhaust duct is permanently posted in text and numerals 3 inches high embossed or cast into or onto metal plates measuring 24 inches by 24 inches and permanently affixed with tamper resistant fasteners directly above the exhaust duct connection location, and, at a height and location as will allow the plate to be visible after the installation of the clothes dryer at the location of the clothes dryer.

- - - 2. Where large-radius 45-degree (0.8 rad) and 90-degree (1.6 rad) bends are installed, determination of the equivalent length of clothes dryer exhaust duct for each bend by engineering calculation in accordance with the ASHRAE Fundamentals Handbook shall be permitted.



Then the manufacturers should come out with a special exhaust duct fitting for exhaust ducts longer than 25 feet, with special alignment notches set at 25 feet to 35 feet, 35 feet to 50 feet, longer than 50 feet, and which only clothes dryers which are rated for those can be connected to those special fittings.