Is there an interior bath, powder or utility room near the stairs?

Sometimes a centrally located sink/toilet/tub/shower does not have a vent through the roof and has what is called an air admittance valve(Studor valve) instead.

This valve is installed so the valve is about 4' high(completely inside the wall) and opens when water creates a vacuum in the system as the water is expelled into the waste pipe which allows air to allow the waste water to flow smoothly.

The only problem with those valves is when they stick open---which allows sewer gasses to come out of them.

We had a foul random smell in our home, turned out to be bats living in the chimney of our wood burning fireplace. If this applies I can help you further.

Skunk living in the crawlspace or a dead animal would be the top two suspects.

@handymac -There is a bathroom kinda close but it does have a vent pipe to the roof.

@captree- The chimney for whatever reason was removed from the inside of the house at some point in its history. (Something we hope to bring back eventually) so I'll have to get on the roof and try to see down it.

@greendesigns- I had the same thought but have crawled under the house and cant find anything. Actually very clean surprisingly. I guess it could be something in the walls but we havent seen a mouse or roach or any critter inside the house in the entire time weve lived here.

Any ideas on a good way to mask the smell until we can either tear out enough walls to find it or it goes away?

My guess would be electrical. Something could be cooking -- the chemicals in plastic can give off some really nasty 'dead animal' odors at high heat. I would check all of your circuit breakers, boxes, electrical outlets, etc. Make sure you unscrew all of your light bulbs from the ceiling and sniff the fixtures.

If you can't find it, I would still suggest having an electrician come out to do a look-see before I started tearing out walls. If you have a dead critter in the walls, the smell would be constant -- and it's usually gone in a week.

Good luck!

Hello again, It is probably not bats, but to check just watch chimney at dawn or dusk ,you would see them coming or going. I think CathyChex could be right. We had outlets on 2 occasions that smelled almost like fish. They were a little warm to the touch. When I removed them they were discolored where one wire connects. Even though the outlets were always live, we could not always smell them. Cinnamon brooms mask odors very well.

This post was edited by captree on Sun, Feb 8, 15 at 21:06

Is there a floor drain located near furnace and water heater? If so, make sure the trap has water in it. My house has a trap primer installed to keep water in the enclosed mechanical room drain trap.

Check the heigth of your plumbing vent pipe. If it is not high enough, a strong Down draft can cause a bad smell to appear.

I have wasted thousands of customer dollars chasing odors reported by tenants not responsible for paying the bills. After 40 years I am convinced that some people are really receptive to power of suggestion. If anyone in the room smells or hears something,they will hear it as well. Part of what leads me to believe it came from servicing child care buildings. After recieving a report an odor was throughout a building,I asked several people what it smelled similar to. The answers within a single building ranged from dead animal,electrical fire,natural gas,dirty socks,carbon monoxide(hahaha anyone smelled co latly?),wet paint,,,,,,,,,you name it. Visit same building 3 times over a month and it only got worse according to staff. Put a dirty rag a in manoise jar,applied a couple drops of ammomia and sealed it up. When the corprate office recieved a call about my incompitance,plan B went into effect. Carry said rag through building exclaiming"I think I found the problem inside the air duct. YEP! That's it,problem solved. I'm not saying that's the case here but but I can tell you that spending 4 or 5 hundred dollars on the problem often makes it go away. BTW,I noticed your odor wasn't described.

intermittent smells are hard to pinpoint.
even harder when descriptions, location &
times of stink occur.
like taking the car to the mechanic for a noise
& car doesn't make the noise until you leave the
shop.
one needs to be on site when the odor occurs.

pinpointing the source is the problem.
gather as much info as possible & post back.

best of luck.