Why does one corner of my house smell like natural gas? Especially when there are no leaks in the house?
September 25, 2007 1:34 PM   Subscribe

I've had a persistent natural gas smell in my house for the past 10 days. The power company shut it off for about 5 days, my landlord went through two times with a plumber to find any potential leaks, and then had to get a city inspector to verify that there are no leaks. So the gas is back on and it's still smells - what's going on and how do I stop it?

If I run the vent over the stove and keep the windows open,
it's okay. But go away for a day or two (or shut the place up
overnight) and you start to get a whiff of it again. The plumber's theory is that it may be triggered by the ignition in my stove or the furnace and because I'm on the bottom floor of a duplex, it's pooling there. Which makes sense because I have an archway between the front (kitchen & living area) and back (bedroom & bath) areas of the house. The smell is always at the very front right corner of the arch at the entry to that hall. The smell always stays up in the front area of the house. We had thought that it was a fissure in the dryer line, but there was no leak detected there, plus he put in completely new fixtures yesterday.

At any rate, my landlord did his part to make sure there's no gas leak. But the smell is still there and I'd like to fix the problem instead of having to constantly run the vent over my stove and keeping a couple of windows open. Not to mention having constant paranoia about gas poisoning.

I'll be buying natural gas detectors for my bedroom and the affected area, but I'm not sure what else I can do. Everything I've read suggests it's due to a ventilation problem. But if I can identify the specific source of where the problem is, I can't really tell him what to fix. It started around the time that the weather started to cool off, so my guess is either the furnace or the stove because both were off during the Summer.
posted by gov_moonbeam to Home & Garden (17 answers total) 2 users marked this as a favorite
How old is your place? I once lived in an 1800s-era apartment that originally had gas lighting. One of the walled-up light fixtures was leaking.

Not sure how to explain the seasonal change, but perhaps during the hotter months, there's metal in a valve expanding just enough to seal the leak.

Anyhow, it's a thought.
posted by adamrice at 1:45 PM on September 25, 2007

Had a similar incident, what a pain to diagnose. Culprit was a partly clogged ignition bar for a water heater - the heater would still work, just part of the area that was supposed to flame didn't, because it got clogged with dust somehow.

Once cleaned, no more smell.

YMMV, obv.
posted by sacre_bleu at 1:50 PM on September 25, 2007

Note that the gas fuel itself (methane) has no smell; the 'gas smell' is hydrogen sulfide, added to it for safety. But there are other sources of hydrogen sulfide.
posted by eritain at 2:01 PM on September 25, 2007

As far as other sources go, I had the smell of what I thought was a gas leak in our house, but it wound up being hydrogen sulfide gas from a somewhat nearby landfill. It would pool up in closed up rooms and hold the smell for quite a while. Do you live near any landfills or pulp mills or rivers?

Additionally, it could be sewer gas. Are there any unused or infrequently used drains in your apartment or maybe right outside of your apartment?
posted by tastybrains at 2:11 PM on September 25, 2007

Call around for a home inspector who has a Tif 8800 series gas detector. They're much more sensitive than the crap the gas company carries, at least here, and the inspector I know has had to go back and show the gas company where he found the leaks they couldn't find.
posted by Myself at 2:24 PM on September 25, 2007

Excellent - thanks so much for the suggestions. To add more information:

The building I live in (2 story duplex) is about 10 years old and sits on an alley in an older (100 years) neighborhood. But there's not really any older fixtures inside of the house or landfills w/in close proximity. If that were the case, I'm pretty sure that my neighbors would notice it too because we're literally cheek to cheek with the closeness of our houses.
posted by gov_moonbeam at 2:54 PM on September 25, 2007

Another thing that smells somewhat like the odorant they use in natural gas is partially burned gas. If you have a gas hot water heater, you may be having an intermittent flue draft problem causing the combustion byproducts to backdraft into the house.

My friend had that problem suddenly appear the other day due to a freak confluence of temperature, too much exhaust, and too little inflow caused by a well insulated house.

It took me a while to realize that's what it was. If I hadn't had gas space heaters when I was younger, I wouldn't have been able to tell the difference between that smell and a gas leak.
posted by wierdo at 2:55 PM on September 25, 2007

Had a smell of gas in the kitchen of the first apartment I lived in, which had a gas stove. The gas company came out but couldn't find anything. The smell went away after we cleaned the kitchen thoroughly; apparently it can get stuck in grime and such.

(The chemical used to add a scent to natural gas is typically a mercaptan, not hydrogen sulfide. Mercaptans also give skunk spray its kick.)
posted by kindall at 3:37 PM on September 25, 2007

hydrogen sulfide is corrosive, it is not added to natural gas. What is added is a mercaptan, which does contain sulfur and stinks at very low concentrations.

Dead rodents in the wall can have a similar smell.
posted by Good Brain at 3:50 PM on September 25, 2007

Hydrogen sulfide may well be in your gas at nose-able levels; it is present in natural gas right out of the well at up to 29%, and is expensive to get rid of. PGE sets a 4ppm limit for H2S in the natural gas they pipe into people's houses, and the olfactory limit, according to the CDC, can be as low as .5 ppb ( almost 10,000 times lower), but I haven't heard of any gas supplier deliberately adding it to their gas. It is highly toxic, a little bit less so than hydrogen cyanide, but of the same order of magnitude, and it is readily absorbed by the lungs. The typical added odorants are "mixtures of t-butyl mercaptan, isopropyl mercaptan, tetrahydrothiophene, dimethyl sulfide and other sulfur compounds."

This is at least the second time I've seen it asserted in AskMeFi that H2S is the odorant added to natural gas, or I wouldn't have bothered to make such a picky point; I suppose the Asker might be a tiny bit less likely to be condescended to if she does not claim to be smelling 'hydrogen sulfide.'
posted by jamjam at 4:21 PM on September 25, 2007

Can you borrow a gas sniffer?
posted by StickyCarpet at 4:44 PM on September 25, 2007

old onions? i have had customers warn me of a gas leak when we are building pizzas with red onions that have been sliced and oxidized overnight in a fridge.

allyl mercaptan is released when onions are cut
posted by ioesf at 5:03 PM on September 25, 2007

A friend's apartment had this problem and it turned out the leak was coming from inside their gas oven, which no one bothered to check for a week or two.
posted by mathowie at 7:16 PM on September 25, 2007

O captan, mercaptan, my fearful flip is done;
'Tis thee and thine mixed in my gas, not sulfide hydrogen.
That thou art not, an error caught by jamjam, Brain, and kindall,
Whose honest facts gave mine the axe, that ignorance might dwindle.
Mercaptan! Thy source, though? On this I'll have to think,
And it's not any easier for living with thy stink.
posted by eritain at 8:58 PM on September 25, 2007 [2 favorites]

So to further confound me, I bought a CO2/Natural Gas detector and alarm at Home Depot after work. And when I got home, no natural gas smell whatsoever! Other than a couple of brief whiffs or two in various corners of the house. And the meter reading for various spots was zero! I did have the vent over the stove running overnight and while I was at work, so I wonder if that got rid of the remaining gas that was in the house. Also, the weather here has warmed up again, so I'm still wondering if that is a factor. The whole business was the gas coincides exactly with the weather getting unseasonably cold and rainy. Although the first time it happened, the furnace hadn't been turned on yet.

Anyhow, I'm bookmarking all of your answers so I can refer back to it when the smell comes back. It sounds like if it's possibly either an issue with the ignition on one of my gas burning appliances (either the furnace or the stove) or it's a venting issue for one of these appliances.
posted by gov_moonbeam at 9:22 AM on September 26, 2007

It might still be sewer gas. Make sure you run all your showers, bathtubs and sinks the next time you smell it, also your dishwasher and your washing machine and anything else that has running water. Also if there is an unused drain in the house, where a washer used to be, a floor drain etc, that can be a culprit -- as can ANY plumbing installation without an elbow. Also, on the roof are vent pipes, sometimes they get clogged or are too short.

My mysterious problem, similar to yours was solved 90% by flushing out a vent pipe on the roof with running water by my friendly plumber.

good luck.
posted by janicea at 6:50 PM on September 27, 2007

We had the same problem recently. Every once in a while we'd get a really strong whiff of the natural gas smell and then it would seem to go away. What we finally found as the cause was our neighbor's gas coach lamps that the wind had blown out while she was out of town.

The gas company employees should be able to track down the source with one of their handheld devices they have for this purpose.
posted by msbaby at 6:18 PM on September 28, 2007

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