Please help!

We have this awful smell in our vents and we have had it almost a month.

The problem is it comes and goes. One day our house will smell so bad one can gag, then other times it doesn't smell at all.

We've narrowed it down to the vents, but we just don't know what to do. Do we just start tearing into our ducks?
My husband has torn apart the furnace and nothing. We smell it the most in our livingroom.

Is it a dead animal? Then why does it come and go?

Is there an animal in there pooping or something? It's an awful smell.

Can anyone help!!

There could be something in the duct, check the duct for any holes or tears where an animal could get in, if you find a hole cut the duct open and inspect, start with the living room duct first ,if you have metal duct you may have to cut a hole in it and check with a flash lite and a mirror, you can patch duct with a larger piece of sheet metal. Good luck, Mike

Mike... could the smell come and go if there is something in the vent? It's very confusing that sometimes it smells bad enough to gag and other times you can't even smell it.

We can even be using the a/c and it doesn't smell. Weird.

I really can't tell you why it might come and go, the only thing you can do is keep searching, Mike

Check for a cracked/loose plumbing vent also. Sometimes depending upon the pressure they can really spell bad as in sewer gas.

This mystry was SOLVED! After a month of this horriable smell, last night I turned on the dishes. Then the smell came. We did not have the a/c on, so we figured we look by the hot water heater.

Turns out a squrriel got in to the pipe between the furnace and hot water heater. It didn't go in the water, just the pipe that blew hot air to heat up the water.

FINALLY the smell is GONE!!
Thanks, hope this can help someone else.