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Old 03-22-2008, 07:07 PM   #1
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Propane smell at furnace exhaust

I posted this before somewhere, but didn't really get an answer to my specific question (at the end).

I have an '08 Safari 25 FB with an Atwood furnace. There is no propane smell inside the trailer and the detector has never gone off. There is an odor at the furnace exhaust pipe. When I removed the pipe, I could not detect any odor; when I reinstalled it, the odor returned.

The furnace hadn't been on since the end of last November, but the odor could be smelled in the past several weeks when near the furnace, sometimes and fleetingly. Before that there was too much snow to get there. Most times I have to stick my nose right against the exhaust pipe. I ran the furnace to see if that made a difference (it didn't blow up)—perhaps a speck of dirt was stuck in the valve and letting a very slight amount of propane through. After I turned off the furnace and let it cool down, the slight odor returned. The tank being used now (and since November) is pretty low. That will increase odor and I believe it takes very little odorant to be smelled strongly.

It cannot be smelled at the gas valve or anywhere else at the furnace. The propane line to the gas valve shows no leak with soapy water. I did find another leak at one of the connections underneath the trailer pretty much under the shower—no soap bubbles showed, but when I tightened the connection the smell went away. That smell was stronger than the one at the furnace exhaust and yet so little gas was escaping it didn't raise a bubble. I also lit a stove top burner and the odorant was extremely strong. This all leads me to think very, very little gas is escaping, but any makes for nervousness. Sometimes there's a very slight odor at the tanks, but none of those connections raise any bubbles either.

My wife says when we're at an RV park, she smells the odorant all over the place, yet I haven't heard of any of those places exploding. It makes me wonder if slight leaks are common.

Has anyone else experienced this odor at the furnace exhaust?

Gene
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Old 03-22-2008, 08:13 PM   #2
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Originally Posted by CrawfordGene
The tank being used now (and since November) is pretty low. That will increase odor and I believe it takes very little odorant to be smelled strongly.

Gene
I think you answered your question with this statement. As you get down to the bottom of the tank, the additive in the propane that makes it smell tends to be more concentrated and when you use the furnace you can pick up that smell. It used to drive me crazy especially since I think that even once the burner turns off, there will be some lingering smell from the chemical. Once you go to a full tank the smell will subside.

One of the easiest ways to check for gas leaks is to pressurize the system and light a stove burner to verify you have gas in the line. Turn off the burner then turn off the gas at the tank. Let the system sit for about a half hour. Go back and without opening the gas valve, attempt to light the stove. If it lights with a good full burner flame, you have proven the system isn't leaking. If it won't light, has a very low flame or goes out right away, there is a good chance you have a leak somewhere.

Jack
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Old 03-22-2008, 09:39 PM   #3
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hi gene

here is your other thread...

http://www.airforums.com/forums/f427...ell-39730.html

and here is a another one on this issue...

http://www.airforums.com/forums/f287...aks-24547.html

get a bottle of soapy water and go at it!

or

given you (or the wife) are still worried, have a qualified rv shop test all the fitting for leaks...

cheers
2air'
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Old 03-23-2008, 01:26 PM   #4
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Crazy about mercaptin

2air, thanks for finding my original post (you are far more efficient and accurate than the Forum search engine, although our cat could probably find something more accurately than the Forum search engine). I re-posted because I was looking to see if anyone had smelled gas at the furnace exhaust. No one answered that specific question last time.

Jack did above, but my situation is a little different. I have smelled the odorant 3+ months after the furnace was last used. I would think the mercaptin would have dispersed after so much time. If there is a leak (and there was in another connection underneath the trailer), both were so small that the nearly empty tank remains nearly empty after 3+ months. If there was more than a tiny bit of gas + mercaptin in the furnace burner and exhaust pipe, when I turned on the furnace it didn't blow up and flames didn't shoot out of the exhaust.

Jack's system for finding a leak by closing the tank valves is a good idea, but might not detect a really, really small leak.

One thing I am sure about is my nose is a better detector than soap bubbles. Where I smelled the leak below the shower, I just tightened all 3 connections—only one turned—about 1/8 turn—and the smell stopped immediately. So the best time to find leaks is when a tank is low, mercaptin concentration is high and nose is fully functional (not during allergy season).

I do remember some people seemed to know a lot about mercaptin (the odorant used in propane and natural [methane] gas). I don't recall anything said about how long the chemical lingers, whether it remains after the propane disperses, and how little it takes to be noticed by us. I thought I read somewhere mercaptin it so intense that even a few molecules can be detected by us.

Actually I'm not so worried as curious. It appears very small leaks, so small soapy water doesn't show them (perhaps the match system suggested elsewhere would work, but I'd rather use my nose), are not unusual.

I think a lesson is to check all the propane fittings regularly and tighten as a matter of sensible maintenance whether or not soap bubbles are used.

I'll be interested to see if anyone else has had a similar furnace experience and whether others smell propane odorant in campgrounds as Barb has (I didn't notice).

Gene
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Old 03-23-2008, 02:52 PM   #5
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hi gene

leaks or curiosity?

from an rv/safety perspective the issue IS leaks...

soapy water or one of the electronically based lp gas LEAK detectors can be used, or the hydrogen sulfide detectors...

some of the models even provide a ppm reading...

fancy gas detectors... is but one of the many sites selling these.

i've seen some hardware stores that RENT detectors too.

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now on the curiosity side...

it's mercaptAn which is more correctly named methanethiol

and is one of many thiol compounds that occur naturally...

Thiols

besides it's use as a tag for natural gas or liquid petroleum, there are LOTS of other potential sources in/around the rv...

normal foods (nuts/cheese) and asparagus (my favorite veggie) along with many plastics give of thiols...

we covered screw driver handles producing 'vinegar' like odors in other threads...

well some plastic containers give off thiol odors too.

also skunks, decaying organic matter, animal poo, and so on....

human breath (the bad sort) also gives off thiol odors...

sometimes these breath odors are benign; related to foods, meds or hygiene...

and other times they represent more serious health issues like gi infections or malignancy (esophagus, stomach, bowel cancers)...

i've seen several folks with serious health issues like these, and the only/early symptom was obnoxious odor noted by them or a spouse.

the 'smell' of thiols can linger from minutes to days, depending on source and nearby absorption...

for example ALUMINUM binds some of the compounds, so aluminum lp tanks that are EMPTY may still smell of mercaptan days or weeks later.

and these lingering traces don't mean there is a LEAK in the system.

mercaptan is often referred to as a "harmless odor" but this is ONLY TRUE in very small concentrations...

most of the chemicals in this class are 'lighter than air' so they rise and dissipate into the atmosphere...

and are broken down by sunlight, ozone in just a few hours.

wanna read more?

Methyl Mercaptan health details

http://www.vngas.com/pdf/g239.pdf

Methanethiol...

so back to RV RELEVANCE...

just because YOU or the mate SMELL it doesn't mean there is an lp gas leak in the trailer system...

i agree regular inspections, using soapy water or a detector is important...

but would NOT support the idea of routinely just 'tightening' the lpgas fittings based on a NOSE

IF no leaks are found using OBJECTIVE tools, snugging the fittings only increases the likelihood of BREAKING a pipe or fitting.

the NOSE APPROACH is a sensitive but unreliable tool and just because we smell these sulfur compounds doesn't mean lpgas is leaking...

and given the altitude at which u live/play all of your gas applicance may need 'adjustments' for this factor.

cheers
2air'
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Old 03-23-2008, 02:54 PM   #6
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Quote:
Originally Posted by CrawfordGene
2air, thanks for finding my original post (you are far more efficient and accurate than the Forum search engine, although our cat could probably find something more accurately than the Forum search engine). I re-posted because I was looking to see if anyone had smelled gas at the furnace exhaust. No one answered that specific question last time.

Jack did above, but my situation is a little different. I have smelled the odorant 3+ months after the furnace was last used. I would think the mercaptin would have dispersed after so much time. If there is a leak (and there was in another connection underneath the trailer), both were so small that the nearly empty tank remains nearly empty after 3+ months. If there was more than a tiny bit of gas + mercaptin in the furnace burner and exhaust pipe, when I turned on the furnace it didn't blow up and flames didn't shoot out of the exhaust.

Jack's system for finding a leak by closing the tank valves is a good idea, but might not detect a really, really small leak.

One thing I am sure about is my nose is a better detector than soap bubbles. Where I smelled the leak below the shower, I just tightened all 3 connections—only one turned—about 1/8 turn—and the smell stopped immediately. So the best time to find leaks is when a tank is low, mercaptin concentration is high and nose is fully functional (not during allergy season).

I do remember some people seemed to know a lot about mercaptin (the odorant used in propane and natural [methane] gas). I don't recall anything said about how long the chemical lingers, whether it remains after the propane disperses, and how little it takes to be noticed by us. I thought I read somewhere mercaptin it so intense that even a few molecules can be detected by us.

Actually I'm not so worried as curious. It appears very small leaks, so small soapy water doesn't show them (perhaps the match system suggested elsewhere would work, but I'd rather use my nose), are not unusual.

I think a lesson is to check all the propane fittings regularly and tighten as a matter of sensible maintenance whether or not soap bubbles are used.

I'll be interested to see if anyone else has had a similar furnace experience and whether others smell propane odorant in campgrounds as Barb has (I didn't notice).

Gene
Sounds like the air/fuel mixture is incorrect.

There is an "air" adjustment for the burner.

If the amount of air is not adequate, then the LPG will not burn completely, which means some of the LPG will be exhausted, which is what you smell.

What can make the air adjustment change?

Lack of proper running gear balance.

What can change the LPG flow?

Check the LPG pressure at the stove.

It should be 11 to 13 inches of water column pressure.

Andy
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Old 03-23-2008, 03:28 PM   #7
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Now I know more than I wanted to know, like asparagus could be in my furnace, or I could by doing it myself. I'd better brush my teeth vigorously before checking the furnace. All that smell in the RV campgrounds could be the people and their pet skunks. I must write "mercaptan" 100 times.

Having broken my share of bolts and piping with my superbly powerful muscles, I'm getting pretty good at not doing so anymore. Checking the tightness of all those gas connections is risky and, I agree, should be done very, very carefully because replacing the broken stuff is a lot of aggravation, means explaining to my wife why I am doing it, and with explosive gas, kind of dangerous.

I'll look at the propane/mixture on the furnace if I can find where the mixture is adjusted. It wouldn't the first thing that was maladjusted on this relatively new unit.

But, can the smell last 3+ months and at the exhaust? The connections before the furnace gas valve did not show a leak with the bubbly stuff nor could I detect any smell at the valve (not a leak detector—how much do those things cost?—but the nose is standard issue at no extra cost). The connections after the valve I didn't check because I'd have to take the whole unit out of the trailer. If the valve is leaking, perhaps the smell travels to the burner and then out the exhaust.

The red is just barely starting to show on the propane valve, so it'll be pretty soon before I switch to the other tank and see if the smell persists.

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Old 03-23-2008, 03:38 PM   #8
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maybe the wild animals are eating asparagus and marking your trailer?

or how about those local gun toting rebel cows?

cheers
2air'
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Old 03-23-2008, 06:09 PM   #9
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It's early for wild asparagus, so I'll go with the flatulent rebel cows backing into the furnace hoping to get some warm milk so the calves get to sleep early.

Glad to get that solved.

Gene
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