Thread: Carbon monoxide issues

So...a chimney should be 2 feet higher and 10 feet away from any building structure, and a gas vent must terminate 2 feet higher than any part of building within 10 feet horizontally...

My biggest concern is of CO getting sucked back into the home when the heater is on. They don't use this fireplace as there is another one across the room. The gas vent in the crawl space shows signs of corrosion and it has big vertical cracks in the rusty areas at the top. If it were mine, I would relocate/replace the entire gas vent asap. The owners are friends of mine and I'd sure hate to lose them. (I'd hate for anyone to be injured, of course)

Am I wrong or should I keep hounding them?

Originally Posted by JC Warner

So...a chimney should be 2 feet higher and 10 feet away from any building structure, ...

Correct. 3 feet high minimum above the roof (measured on the high side of a sloped roof) or 2 feet higher than any part of any structure within 10 feet.

... and a gas vent must terminate 2 feet higher than any part of building within 10 feet horizontally...

Close. A gas vent must meet minimum height above the roof (with the minimum height depending on the slope of the roof) or 2 feet higher than any vertical obstruction within 8 feet (not that the 2 feet difference matters in your case with the chimney within inches of the gas vent).

My biggest concern is of CO getting sucked back into the home when the heater is on. They don't use this fireplace as there is another one across the room. The gas vent in the crawl space shows signs of corrosion and it has big vertical cracks in the rusty areas at the top. If it were mine, I would relocate/replace the entire gas vent asap. The owners are friends of mine and I'd sure hate to lose them. (I'd hate for anyone to be injured, of course)

Am I wrong or should I keep hounding them?

Based on code requirements ... that gas vent needs to be higher, at least 2 feet higher than the top of the chimney structure.

The storm collar at the flashing of the gas vent through the roof is missing.

Based on your description of the condition of the gas vent, the gas vent should be replaced.

With regard to location of the gas vent near the chimney ... hopefully Bob H. will reply as he can give all kinds of reasons that what the code permits does not always work as the code intended.

Thank you, Jerry!

Speaking of chimneys, this is one of my favorites. In 1992, we had a 6.8 earthquake centered in our valley. Most of the damages were masonry/rock chimneys falling over. Personally, my own brick chimney fell through my cathedral ceiling and into my living room. A lot of people kept the bottom of their chimneys and then added metal flues on top, but apparently some people didn't get the memo about how high to make them.

Good pick up JC. Any sort of noxious gases anywhere close to a chimney are just asking to be recirculated down the chimney into the home. This can happen with a stink pipe (DWV stack) for instance. In this case, you have what may be an air cooled chimney in close proximity to flue gases. The concentric air space in the chimney, not to mention the chase itself, can allow the fumes to fall down into the home.

That B-vent is in a horrible location for several reasons: adverse wind effect due to proximity to a building obstruction, too much cold exposed vent prone to condensation and weak draft, inadequate separation from chase for water management or snow, and an improperly flashed B-vent roof flashing. Good pickup JP on the storm collar.

The B-vent is not supported in three axis at the offset above the roof nor every 5 feet. The damage at the top appears to be longstanding condensation to the point the rain cap was recently replaced. There is staining on the chase siding behind the B-vent--is this rust or byproducts of combustion/ heat?

The chase should be razed. With a woodburning fireplace in close proximity to gas and the obvious age of the fireplace and B-vent, I'd recommend they replace the fireplace with a gas direct vent vented vertically through the roof per the listed instructions and replace the furnace with a CAT IV condensing furnace sidewall vented if possible. If this vent is to be left in place, I would recommend a certified pro perform combustion analysis first to determine if a CAT I B-vented appliance can possibly work here. Even with new B-vent, it may draw like a 3 yr old with crayons. Yes, the B-vent would have to be extended 24" above any obstruction within 10 ft. but the height is based upon roof pitch and the listing of the appliance. This would add more cold vent further exacerbating the venting problems.

On the stubby, I'd still want a Level II because a seismic event can weaken the base of the chimney sufficiently to cause failure of the remainder down the road. At the very least, I'd be worried about the flashing and what sort of unit is using B-vent where a direct vent should have been the obvious choice. With that vaulted ceiling, I'll bet it doesn't draw with a hoot in all weather either. The adverse wind effect from proximity to such a steep roof cannot be over stated. I've seen venting flow issues from such roofs >20ft away.

In all cases, I'd recommend installation of a low level unlisted CO monitor on each floor and within 15LF of each sleeping room.

Thank you, Bob, for all of your great information. I will pass it along to my friends.

Here's is something interesting on this issue: Discipline for Heating Contractors in North Carolina CO Poisonings - JLC Online

Jerry, thanks for the article. I remember seeing that on the news. So tragic and senseless.

To Bob, Jerry or anyone that knows,

Regarding storm collars: since Jerry noticed one was missing on my original post, and frankly I'm a newbie, I was trying to find in my books about where storm collars are required. Driving around my town, I noticed that probably 50% of chimneys and gas vents actually have them.

So my question is: are storm collars required on both chimneys and gas vents? Anything else?

Thank you!

A storm collar is a listed component of the listed vent system, whether B-vent, L-vent, pellet vent, AL29-4c special gas vent or factory chimney. Masonry chimneys have roof flashing per the building code. It's also just common sense--you don't want rain/snow/ ice penetration into the structure. Listed roof flashing holes are much larger than the pipe diameter by design. They are intended to spill some heat keeping the roof deck cool. This is not so much of a fire hazard with gas venting but is with L-vent and certainly with factory chimney. The storm collar should not be caulked down tight forming a seal but allowed to breathe. You'll notice some listed roof flashings now have ventilation slots from the factory to ensure this cooling.

All offsets must be supported vertically and horizontally so there's no strain on the gores (joints) of the elbow. Unsupported ells can and do blow apart regularly. When you get more than 5 feet above the roof, you must have supports, whether two guy poles, cables-whatever. This means every 5 feet as written in the listed instructions of most vent mfrs. such as using 'wall bands' (as used here at the chase cover) up the side of a building.

Thank you, Bob! Now, if only I had a dollar for every missing collar around here, which doesn't make much sense since we are in snow country.
Everyday I learn something here. Thanks again.

Around here, storm collars are another one of those items that code or installation instructions may call for, but local AHJs regularly don't require. I,too, rarely see them. I reviewed some illustrations on the internet and saw one showing it caulked to the vent. Which reminds me that I rarely see the boot jack caulked or sealed to the vent.