Natural gas smell at exhaust of high efficiency furnace

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Old 11-14-15, 08:40 AM
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Natural gas smell at exhaust of high efficiency furnace

Need your expert advice:
I have a Carrier Infinity 58MVC furnace that was installed in August 2009. I recently had it serviced because I could smell natural gas emitting from the exhaust pipe. (Which is on the side of my house, I only have one pvc pipe, the other intake is on top of the furnace in my basement)
Here was his comment :
"furnace tune up removed burners and found cross overs rusty and partially blocked, likely the issue of a gas smell at exhaust, cleaned burners and sensor, vacuumed , checked combustion and operation
low .69
med. 1.7
high 3.2
checked combustion and operation all ok

I have a new puppy that I have to take out several times a day and I'm still noticing an intermittent gas smell.Just intermittent whiffs, and I have a VERY sensitive sense of smell. When it was a stronger smell, I did run in to check my Infinity thermostat that blinks when the burner is turning on, and it was blinking....it didn't smell minutes later. It happened again this evening but again the "ignition" light was blinking. I have a gas oven and a gas dryer and the smell is weaker then when either of those ignite. Is it dangerous? There is no smell inside. Should I pursue this further?

I called the company that serviced the furnace and they said to give it a week and try to notice when it was happening. Is this a normal exhaust situation with a high efficiency furnace? I have noticed that since it was serviced it fires through the stages much quicker so that's an improvement.
Thank you in advance for your comments!
 
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Old 11-14-15, 08:43 AM
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Secondary heat exchanger

I did Google the Model and Make and saw the problems with the secondary heat exchanger but the technician checked that and said it was fine. I should also note that the technician had the very same furnace in a Bryant model. The Infinity smart thermostat did report ignition problems.
 
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Old 11-14-15, 08:49 AM
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Sorry if this posted wrong, it was in addition to my first post about the natural gas smell at exhaust.
 
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Old 11-14-15, 09:15 AM
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Welcome to the forums.

It is normal to smell a small amount of natural gas at the start and during the burning cycle. Usually more towards the start of the cycle.

Years ago the exhaust gases were all discharged up a chimney so that the smell was never noticed. Now with direct vent applications the flue gases are discharged at/near ground level.
 
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Old 11-14-15, 09:30 AM
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Question for another dog lover , why is the intake not run to the outside? Is the location of the furnace such that there is no restriction (or competition) for the combustion air?

Bud
 
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Old 11-14-15, 10:33 AM
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Good question, installed the HE furnace where the previous one was, and there wasn't any room for another pipe unless we drilled through concrete and made a major renovations. The house is on a hill so it would've been extremely involved...The tech said that the reason my burners were already showing a little rust was because of the inside intake and the higher humidity inside. I definitely will have it checked every year now that I know it's prone to rust.
 
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Old 11-14-15, 10:36 AM
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Thank you PJ that gives me peace of mind. Do those combustion rates look satisfactory?
 
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Old 11-14-15, 04:36 PM
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Most condensing gas furnaces have a viewing port which allows you to observe the burners.

I'd cycle the furnace several times and observe the burner ignition through that viewing port. You should see all the burners light promptly and smoothly once the main burner gas switches on. If there is a delay in ignition of one or more burners, that needs to be corrected.

<<It is normal to smell a small amount of natural gas at the start and during the burning cycle. >>


Ummm, I don't know that I agree with PJ Max on that. Usually all burners should light smoothly and promptly and there shouldn't be a noticeable gas odor.

However, I am familiar with you human bloodhounds with very sensitive noses. You can smell stuff at VERY low levels! That may not be a problem.

You have had a tech who identified the burners nopt lighting properly and corrected the problem. I'm suggesting that you do your own visual check to confirm that the burners are lighting reliably. Beyond that, you probably don't have a significant problem.
 
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Old 11-14-15, 04:45 PM
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We're walking a fine line between noticeable gas smell and a little gas smell.

EVERY gas device smells a little like gas when it lights. I can smell the gas stove in my kitchen when it lights. I always have been able to smell it. It's perfectly normal.

I can smell a faint odor of gas at almost every flue I work near. I can smell it at the exhaust vent at a dryer outside.

Everyone should be able to distinguish between a faint gas smell and a major gas smell.
 
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Old 11-14-15, 05:29 PM
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<<I can smell a faint odor of gas at almost every flue I work near. I can smell it at the exhaust vent at a dryer outside. >>



Sounds to me like you may be one of those people with an exceptionally sensitive sniffer. I don't notice such things myself.

<<Everyone should be able to distinguish between a faint gas smell and a major gas smell. >>


That's the problem. People DONT know.

I worked for years as a gas utility repairman, and often I was the first responder on gas odor complaints.

There were people who'd been living with a pretty strong gas odor for a long time. People DON'T know, pretty often.

The most amusing thing was that WIVES pretty often claimed to smell a gas odor, while HUSBANDS pretty often poo pooed such a thing. When I showed up at people's door, I knew that the odds were that the guy was going to be in trouble! Dollars to donuts there was a gas leak there that the wife had been smelling but the husband was not.

I've always guessed that women had better noses than men, on average.

Still, the number of gas leaks that were actually a hazard was quite small. But the problem is, that people DON'T know, so the utility treated every gas odor complaint as a top priority call.

And every once in a while, you did find a gas leak that WAS an imminent hazard. Those COULD be scary!

(The most hazardous gas leaks came from gas mains buried underground which could saturate the ground all the way u[p to a building foundation. That could causes explosive levels of gas to accumulate in basements or crawl spaces, just waiting for an ignition source to blow the building off its foundation.)
 
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Old 11-14-15, 05:33 PM
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(The most hazardous gas leaks came from gas mains buried underground which could saturate the ground all the way u[p to a building foundation. That could causes explosive levels of gas to accumulate in basements or crawl spaces, just waiting for an ignition source to blow the building off its foundation.)
As witnessed by all the gas explosions we see on the news and especially in NYC.
 
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Old 11-14-15, 07:44 PM
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Thank you Seattle,
Yes I have been told that I am a human bloodhound many times, and yes I'm a woman. I do all the handiwork and maintenance around my home, my husband is mechanically challenged. I actually have to leave the room when I turn on my gas stove, it unfortunately doesn't vent outside, and I hate the smell! Thanks for the tip, I would've hoped the tech that I had out watched it cycle through but you never know. I appreciate your input, I will continue to keep a eye (or nose) on it, but I feel better knowing an intermittent very faint smell is probably normal.
 
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