smelly pipes, smelly bathroom

[handsrusinkc]

I have a somewhat unique situation:

I have a crawlspace that is heated by a vent that comes down from the attic. I suspect that the heating (and, unfortunately, airconditioning) is there so that the pipes won't break in freezing weather. I am in Kansas City.

Only in cold weather, the heat that pumps into the crawlspace, causes a sewer smell to seep up through the bathroom floor and makes the bathroom smell like a sewer. I fixed most of the problem by fixing a hole in the floor under the sink cabinet that someone left there...the idiots.

There are still small areas where the smell comes up, but it isn't noticeable...

Now the concern is that the closet where the crawlspace access door is located sometimes smells like a sewer.

Are pipes supposed to smell like a sewer? I suspect not.

By the way, the smell is worse when I am running something, like the shower or the washing machine.

Is there a good way to find the leak other than just crawling around down there smelling for the greatest stink? how does a plumber find the leak?
P.s. There is nothing dripping anywhere down there.

[jadnashua]

IF the heating system ductwork is not balanced, when the fan runs it can create a vacuum which can pull in sewer gases from leaks or possibly even from the roof vent. There could be a drain in the crawl space for the evaporator of the a/c unit and/or for the furnace if it is a high efficiency condensing one, and when it doesn't run, the trap could dry out (if it even has one), and allow sewer gasses to be drawn into the ductwork. Sealing all of the seams in the ductwork may help. Don't use duct tape - use the foil tape instead. It is sold with paper release one one side you pull off to expose the adhesive. The ducts must be clean before you install. My unprofessional opinion.

[handsrusinkc]

When I run quite a bit of water through the pipes, a sewer smell comes out of them. Which, to me, means there is a leak in the pipe. I've crawled around down there and looked but can't find one.

Is there a technique that a plumber uses to find a leak?