Should Gas Appliances Smell Like Anything?

Lately I've been noticing a specific smell in the house. It's something I've smelled before in other houses I've visited or lived in with gas appliances (heat or otherwise). I'm going to guess that it is a "burned gas smell". It smells faintly like unburned gas and something else, like 'heat' i guess, even sometimes a little bit like kitty litter. I know that's a bit silly, but I can't think of anything else that smells similar, and on top of that my nose doesn't work so well anyways. In fact, the Missus says she can't smell what I'm talkinga bout at all.
We have a 2-story house w/ no basement. There is a gas boiler and a gas water heater on the first floor under the stairwell, behind some vented doors. They both vent into the same chimney via a Y-pipe. It is passive- i.e. no fans, turbines etc to blow the exhaust out- just heat and gravity. The space that these are in is definately where the smell is coming from, and AFAICT it's the boiler that's doing it. It's most intense in that end of the house when the boiler has been running a bit. When the boiler is not running, I can sniff around it and still smell it. I fired them both up individually and held a cig lighter flame near the cold air intakes of the exhaust tubes for both devices. The water heater definately draws the flame inward (indicating a strong upcurrent). The boiler's exhaust is kind of hard to tell because of the way it is shaped. A stick of incense, maybe....
I have a brand new Nighthawk branded CO detector that I got from the Borg. It is mounted in the stairwell above the same stairs that the boiler and water heater are underneath. Finding the right place for it is a bit of a challenge- away from doors (drafts falsely give low readings), away from the appliances (which may falsely give high readings), etc. You can look at my house as a cube, and it is mounted about in the dead center of the whole thing. It always reads 0ppm. According to the manual, it won't readily display anything under 30ppm, but it has a sequence that you can use to display the 'high reading' which it will show down to 19ppm. Still, it always reads 0ppm. I removed it from the stairwell once and set it on a table in a relatively close proximity of the boiler and water heater, expecting to get some (albeit false) reading out of it. Still 0ppm.
I don't really know how 'normal' it is to smell "this smell". Is there:
1) A way to test a CO detector to ensure it isn't a factory "dud"? 2) A way to otherwise test for CO levels in the house and verify safety? 3) Someone I can call to look at the appliances and ensure they're functioning properly? Is this a job for the standard "Heating/AC" guys in the yellow book, or someone else? Do they usually rove around them with some sort of "sniffer"?
Thanks for any and all suggestions. I understand that "uhh... i smell this smell" doesn't tell you much.
-phaeton
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I mentioned something like this to my local neighborhood HVAC tech. His response was that it was probably dirt in the furnace and if the smell bothered me I should clean it with compressed air (and yes, furnace was dirty).
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tell your gas company you smell gas and they will bring their sniffer to your home in one hour 24 hours a day in buffalo ny. call them now.
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If I call them out:
1) Will it cost anything?
2) Do they check only for gas leaks (not CO)?
3) If it's a specific appliance, do they red tag and shut down the appliance only (they've all got their own gas valves) or do they kill gas to the whole house? I could get by without gas for a day or two.
4) Is there anyone I can call out to test for CO production from appliances (if the gas company doesn't do it)?
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Like bill said, call them now. Better safe than sorry.

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phaeton wrote:

There are two typical smells from a gas furnace. One is the actual gas. It does not smell like "burn" but very distinctive. If you are smelling that or think you may be smelling that, call your gas supplier and they will check it out for you. They want to keep you safe. I might add that if they find anything unsafe, they will shut off the gas right then and you will not get it back on until it is fixed. They have been known to make some simple repairs on the spot for you for free as well if you are lucky.
Other than that it is usually burnt dust. That means getting the furnace cleaned and making sure you have a good filter in place to reduce it in the future. If you don't have a furnace filter, that is why you have the smell.
--
Joseph Meehan

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On Mon, 23 Jan 2006 23:53:08 GMT, "Joseph Meehan"

Joe is right, but the smell he's talking about is not the actual gas Rather, it is the aromatic additive put into the gas by the suppliers to make the gas actually detectable by people. That's a safety feature, and the smell is unpleasant and totally different from anything else most of us would smell in a routine life.

Burnt dust smells pretty much like you'd expect it to, and the smell typically is not of long duration, usually for the first few hours you run a furnace after not running it for a long time. I experienced this often with my old gravity furnace (bless Olivia the octopus, ca. 1910, who started life as a coal-fed furnace and then was converted to natural gas some time in the 1950s or 1960s and was unrelentingly reliable if not efficient) and wasn't bothered by it.
The "natural gas" smell is offensive, though, and the MINUTE you smell it, you should call your local utility company.
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Yeah, that's just it... it's not "raw gas" smell, and the smell i refer to is repetetetive. If it were dust it would have burned away weeks ago.
I also realize that you cannot smell CO, but if CO is often caused by an incomplete combustion, would there be other, more smelly things created by that process?
thx
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phaeton wrote:

I can only talk from the one personal experience I had with CO. I was one of the lucky ones of maybe 30 people who were effected. I was sleeping on the floor at the time. The four who were most seriously effected were sitting up at a table. There was no smell at all, no one reported any unusual smell. About half of the people involved reported being effected by the CO. The four were all treated by the emergency crew and one went on to a hospital. No one suffered any serious or lasting problems.
I would not count of smell as an alert for CO.
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Joseph Meehan

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KLS wrote:

Very true. The stuff is called mercaptan and it takes very little. It is burned along with the gas so you don't smell it at all under normal conditions.

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"Totally different from anything else most of us would smell in a routine life"?
Depends. Does your "routine life" include rotten eggs or skunks?
The additive is methyl mercaptan, aka methanethiol - CH3SH, or ethyl mercaptan, aka ethanethiol - C2H5SH.
["mercaptan" and "thiol" are terms for the "SH" bond]
_Intensely_ aromatic. H2S (Hydrogen Sulfide - most people only come into contact with this from rotten eggs, but it's the "sour" in "sour gas", and is highly poisonous and corrosive) and skunk aroma are mercaptans too and smell quite similar.
A drop of this stuff will stink up a building with poor ventilation something awful. You can smell this stuff as low as 50PPB (parts per _billion_).
It's potent stuff.
If you smell it, call the gas company ASAP.
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Chris Lewis, Una confibula non set est
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phaeton wrote:

As mentioned, you can ask the utility to come out and check. They are usually very good about that and can be helpful. Understand that if there is something suspicious, they may red-tag it.
Besides the well-known odorant they deliberately put in the gas, there is the possibility of odors from "aromatic hydrocarbons" present in the gas. This is a very odd smell which defies description. It is almost always produced because of improper/incomplete combustion which can be due to a fault in the burner or insufficient draft. This has nothing to do with CO and instruments may not show excess CO (which you can't smell anyway).
The "bad odor" CAN be a warning though and shouldn't be dismissed lightly.
Jim
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Right after I installed it I smelled something other than that. I got my son (figuring he had a better sense of smell than me) to hunt it, and he isolated it to the valve. I called the utility and they sent someone out with a sniffer. He tracked it down to a loose fitting in the valve. He flagged it and said that if it wasn't fixed in a week he would have to shut it down. The water heater people came out and fixed it (I was so relieved it wasn't my installation!)
The utility man said that the small leak I had was pretty harmless, but obviously had to be fixed. A leak big enough to be dangerous is overpoweringly horrible smelling; there is no uncertainty about it.
So, my guess is that you don't have a problem. But having the utility check it is free.
I have two CO detectors. They aren't all that expensive, and the odds of two malfunctioning...
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