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Question DetailsAsked on 10/14/2015

I have a sweet chemical odor in second floor bedroom in wall when cool. Recently swept Chimney on outside.

For a few months, I have had this sweet almost acrid, phosphorus, flinty chemical smell in one room of the house at night. It has a faint mothball smell. We've checked for animals, had the chimney and ash trap cleaned, lit the fireplace to pull the draw out of the house, used air cleaning machines, opened windows and the smell came back tonight and woke me up. The smell stays on my clothes and hair for a short time. 1930s house. Lived here 11 years with no problems. Bugs, chimney mold, animals, sewer [pipe leak? It's odd it comes when it is cold at night. Who do you call for a sewer pipe leak?

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Here are links to a number of prior questions about similar issues which might help -

I am going to toss out some more possibilities - you will have to investigate or decide if potentially applicable to your case.

Since you say nothing abouty it being putrid or sewer or urine smelling, I would guess that rules out leaking toilet seal, significantly broken sewer pipe, overflowing septic tank/leach field (yours or neighbors), or dead animals, though not ruling out a water leak or liquid-only minor leak from a drain pipe or fixture like from basin or tub/shower, or shower pan leak.

Mothball smell has me a bit puzzled - assuming you are in a single-family dwelling.

Sweet, acrid, flinty, phosphorus - those could all apply to creosote - do you know what that smells like ? Assuming no neighbor has recently installed creosoted (railroad tie ?) retaining wall or such, in cold evening smell in the fireplace to see if coming from there - freshly cleaned or wet chimneys can smell like that from the newly exposed creosote (cleaning removes the loose stuff only, not the stuff impregnating the brick or lining). If chimney has not had a couple of good long fires since the cleaning, could be it.

Could also be, especially if damper is not closed, warm house air going up chimney at night, then as it cools at the top cascading down the roof into a bathroom roof vent or window. Did you have the chimney inspected when it was cleaned ? Is there any chance water is getting into it from a missing cap or cracked crown mortar, seeping into the house and pulling creosote smell with it ?

To check - try (depending on what type of surface you have) taking plastic sheeting or flattened out garbage bags (duct taped at any seams needed to cover fireplace) and tightly tape over the fireplace opening for a couple of days and see if that solves it. If so, you know the source - have a couple of decent (but don't flame the chimney) fires, starting with newspaper starter bed to get it well heated up. However, if problem is water in the chimney leaking into the house, this will NOT solve it, though taping over the chimney to test might reduce it by cutting down airflow from the chimney through cracks into the house.

If not that, could also be sewer gas coming out your vent stack on the roof, settling down into a bathroom or kitchen roof vent hood whose flapper is stuck open, or into a window, or even cascading down off the roof and right up into the eaves where it gets into the attic and then settles into the house. Would require, when you can smell it, going outside and moving around (and in attic if accessible) and maybe getting up on a ladder to the roof edge to smell generally downhill of the main stack vent pipe (will be wide open pipe penetrating roof and sticking up several feet, no cap (or should not have one), about 2" diameter usually. Would not mean yo uhave a sewer problem - can happen in different climatic conditions where your house stack acts as a vent for the street sewer, and also sometimes after the street sewer is cleaned and it opens up a pathway through previous sewer backed up liquid for the sewer gases to flow straight into sewer pipe, then up the vent stack. Mine does this in the winter on calm cold days because I am at the uphill end of the sewer - happens when the air vents in the manholes get blocked by ice and snow. Knock the holes clear with a hammer, presto the noxious venting becomes unnoticeable, though still visible as "heat waves" coming out of the vent.

One other possibility - leaking flue from furnace, leaking partly burned exhaust gas into living space - in walls or in attic due to rusted flue or pulled-apart joints - especially strong if oil fired but can be acrid with gas too - though with gas fired appliances commonly hot metallic and a bit sulfury smelling too. See if you can time it against furnace firing, or if temps are not too cold turn furnace off for some time and see if smell dissipates, then turn on and see if starts right off in the next 15 minutes or so. If you can't smell it at the furnace when firing (burning wires or such) but can smell it at flue on roof (if you can get up there), then likely leaking flue pipe - Heating and A/C contractor for that cause. Can also be, in calm cold days, cooling of the exhaust flowing off the roof and into an opening into the house.

Another possibility if 1930's house - did it originally have coal or oil fired furnace ? Could there be old coal residue or coal bin getting wet - or an old buried oil tank leaking very old, tarry oil, the smell from which is pulled upstairs by the nighttime (colder conditions) more frequent furnace operation - likely being pulled into the furnace area and from there into the ducts ?

Remote possibility - stagnant sump pump sump ?

Common event, but usually smells like raw sewage or hydrogen sulfide - unused sink, shower/tub, washtub, washing machine drain pipe, or floor drain trap has gone dry, letting sewer gases into the house - sole by putting a couple tablespoons baking soda down the drain followed by a 1/4 cup vinegar, let fizz a couple minutes, then pouring 1/2 to 1 gallon of water with lemon scented dish soap (a squirt) into it to flush and fill it up. Redo the wataer with soap or baking soda every 3-24 months depending on your house humidity (and whether ever used). Does not hurt to do too often - like put on calendar for every year and see what happens, more often if needed.

Otherwise, a plumber or sewer and drain cleaner/repair contractor can do a smoke test of your drain pipes - put a smoke bomb or generator smoke into the pipes with roof vent pipe blocked off, and see if smoke comes out somewhere in house. Can also be done with banana oil or vanilla but you can't see them, but will tell you if leaking. (ALL drain traps have to be fully water filled before doing this, to prevent leakage into house through a trap).

My guess, especially since chimney was recently cleaned and because you said smell sticks to your body and clothing, would be leaking flue or chimney creosote because hydrocarbon smells stick to clothing well - but if started BEFORE the cleaning then it could be fresh creosote from the cleaning if you have not used the fireplace several times, or from a leak. DOes it get stronger after rains ?

Also - what is near that room - any appliance that could be burning dirty, venting gases, etc ?

Or electric panel - sniff near that, open door of fusebox/breaker panel (those designed to be opened by homeowner) and carefully sniff for smell of burning insulation. Could be a loose connection in the box overheating as it arcs, gradually burning off the insulation.

Another thing if ONLY at night - could there be an animal living in basement, crawlspace, attic that is causing this smell - either an animal like squirrel family who comes "home" at night and who are not quite Disney-clean in their bathing habits, skunk or polecat or wolverine if you know what they smell like, bats also have a strong smell - or could it be animal and urine/ xxxx smell from animals nesting in the house ? Sniffing around in each possible hiding space should lead to it if that is the cause - or call a Pest Control or Animal Removal company who hunts for AND removes animal infestations.

Possibility of rancid grease in kitchen exhaust fan or its ducts ?

You did not say WHAT room - if you want, answer back with what floor this is on, what is over and under it and next to it, and what ducts might pass by it or directly over/under it, etc. Use the Answer This Question yellow button right below your question to answer back, if you wish.

Answered 3 years ago by LCD

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