We recently moved into a townhouse that has a finished basement, a main and second floor. When we open the door to our deck on the main floor, we smell a rancid, gassy like smell in the stairwell to the basement. The smell doesn�t come into the main floor and doesn�t go into the basement area. With the door to the deck closed, we don�t notice the smell. We also don�t notice the smell with a second floor window open and the door to the deck closed.

The basement and stairwell had carpet which we thought was the problem but it was removed about two months ago and the smell remains.

At the bottom of the stairwell to the right is a furnace room and under the stairs is a storage area. Neither of these areas has the smell. We�ve had the gas water heater and furnace replaced. Both installation people didn�t know what the smell was. We've had them back a second time to check it out.

At the bottom of the stairwell is a full bathroom with a whirlpool tub that we've taken showers in. The bathroom appears to have been added at a later date, the house was built in 1985. Nothing in the bathroom has an odor like the smell. We�ve smelled the drains in the sink and tub, the openings in the whirlpool tub and the gap between the tub and floor.

We've done many experiments, closing/opening other doors/windows, putting towels in front of doors, sealing off openings, etc.

There is an access hole for the tub in the furnace room which I checked. There was no smell evident when I opened it.

I cut a new access hole in a closet on the other side of the tub and didn�t notice any smell. The concrete floor had been cut to install the drain then the hole refilled. I don�t know much about plumbing but there doesn't look like there is a vent pipe directly attached to the drain pipes.

We have a dropped ceiling so I checked above the panels all around the basement, nothing unusual. No dead animals. We have a humidifier in the basement that doesn�t collect an excessive amount of water, so I don�t think it�s a moisture issue. Nothing is wet or damp.

I haven�t checked to see if the smell is noticeable when any other main floor windows are open.

Does anybody have any ideas of what this smell could be and why we only smell it when the door to the deck is open??

Any idea of how to get rid of it??

Thanks for your help.