Weird fertilizer/gassy smell in the basement (from the water heater?)
December 30, 2013 7:36 AM   Subscribe

I was away from the house last night when I got a text from my wife about a strange "fertilizer" smell coming from the basement of our house. I came home a few hours later and smelled it immediately - hard to describe, but a slightly acrid, recognizable chlorine-y scent reminiscent of a garden center. It was noticeable on the first floor but stronger in the basement. I sniffed around for a while but couldn't locate an obvious source. The only thing I could find that was awry was that the pilot light had gone out in the water heater (only time that's happened), which is suggestive of a chimney backdraft. I relit the pilot without issue and verified that the water heater was venting correctly with a stick of Nag Champa. Multiple C02 detectors in the house detected nothing. We'll have an HVAC guy come out ASAP, but I'm wondering if anyone else has experienced this and whether I'm diagnosing the issue correctly. Is this what water heater fumes smell like? We've lived in the house for a year, and this is the first time it's happened.

We're in Chicago, and yesterday was cold and windy (and there was an exhaust fan running in one of the bathrooms) - all conditions that seem to contribute. The boiler and water heater are both old and vent through the chimney (no fireplaces), which has a steel liner.
posted by ndg to Home & Garden (15 answers total)
CO2 and CO are odorless, so it won't be that - that's why you need detectors for those. "Fertilizer" to me suggests ammonia, which has a very distinctive smell, but I don't know what would be leaking ammonia - the only common household use of ammonia is as a surface cleaner, so I guess it's worth checking you don't have a spilled bottle of ammonia under a sink or something.
posted by spielzebub at 7:47 AM on December 30, 2013

Natural gas has a stinky additive, but it's sulfur-y. I know what you mean by "garden center smell" and I think you'd be able to differentiate.

You might check for damp areas in the walls and floor, especially where it might be soaking into something. Fresh wet stuff can smell composty just before it starts smelling moldy.
posted by Lyn Never at 7:53 AM on December 30, 2013

Do you have a sump in your basement that could have accumulated something with an Oder?
posted by HuronBob at 7:58 AM on December 30, 2013

Have you got a floor drain in your basement or a rarely used sink/shower? Could be the smell is sewer gas passing through an empty P-Trap. In which case a bucket of water in all the traps would mitigate the problem.
posted by Mitheral at 7:59 AM on December 30, 2013 [6 favorites]

Do you have a shelf or storage in basement that has old cleaning. paint or gardening supplies? I've seen very old containers of products finally rust out and then rapidly leak out the contents.
posted by nogero at 8:00 AM on December 30, 2013

Some water heater tanks are enclosed in uncured concrete that solidifies if the tank springs a leak.

Not sure what byproducts/chemistry is involved and what it smells like, but since you had a pilot out condition, is it possible you have one and this was the problem?
posted by FauxScot at 8:07 AM on December 30, 2013

Mice. I bet it's mice coming in from the cold and making a nice, urine-soaked nest somewhere in your basement.
posted by MrMoonPie at 8:10 AM on December 30, 2013 [3 favorites]

Like MrMoonPie, my first thought was animal urine. If you have a dog or you can borrow one, let it down in the basement (on a leash, so he doesn't ingest anything he's not supposed to) and he will lead you to any animal nests.
posted by desjardins at 8:17 AM on December 30, 2013

Well, since we're considering mice, don't rule out bats.
posted by HuronBob at 8:18 AM on December 30, 2013

My first thought was animals too. Perhaps even a dead one in a wall or the like? Those can reek with a sort of decomposing/fertilizer-y smell.
posted by Lutoslawski at 10:25 AM on December 30, 2013

Yea, we had the same problem every winter from mice coming in and building nests. It always stunk and got worse if one died, I really don't miss that house...
posted by lpcxa0 at 11:48 AM on December 30, 2013

There should be a pressure relief valve on the top or side of your water heater. Any sign that water/steam has come out there? You could put a cup or pail under the exit to check.
posted by weapons-grade pandemonium at 12:08 PM on December 30, 2013

Thanks to everyone who took the time to answer. Without being able to post the smell, this was a longshot at best, but for posterity: the smell was finally diagnosed as a dying hydronic zone valve powerhead on the boiler, which has been slowly burning itself out since last night. Really odd, because there was a distinctly organic note to the smell.
posted by ndg at 3:24 PM on December 30, 2013

Could be the smell is sewer gas passing through an empty P-Trap. In which case a bucket of water in all the traps would mitigate the problem.

I think this suggestion from Mitheral is the correct answer.

The running bathroom fan reduced pressure in your house, and the wind blowing past the house reduced it even further (by sucking it out via the Bernoulli effect), and the two together reduced inside pressure enough to pull some gas from the sewer up through a drain into the house. In a strong wind, the drain wouldn't have to be completely dry.

Then when the wind stopped blowing or in the wake of a gust, outside pressure went back up and the low pressure inside the house sucked air back into the house through the chimney (the backdraft you mention) and blew out the pilot.

That doesn't mean the "hydronic zone valve powerhead" isn't bad, but I think at least the organic component of the smell came from the sewer.
posted by jamjam at 5:45 PM on December 30, 2013

Really odd, because there was a distinctly organic note to the smell.

posted by werkzeuger at 6:10 PM on December 30, 2013

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