John G wrote:
On Wednesday, February 10, 2016 at 3:07:14 PM UTC-5, Bob wrote:
Is it possible to stop the stack effect (rising up of warm air causing
dirty crawlspace air to be sucked into living area) by installing an
exhaust fan in the crawlspace (obviously all vents are covered except
the exhaust vent) and creating a negative air pressure?

Or would this just create a convection effect where in cooler part of
the house, air migrates down into the crawlspace, and in warmer area of
the house, air rises upwards and pulls the crawlspace air into the
living area?

If air is leaking in one direction into the living area, installing a fan to suck air out seems like it would be pulling air from the living space. I would get down there and start plugging holes and sealing gaps and maybe install some sort of vapor barrier under the floor joists.

Ditto.
Dirty air? May be Radon gas? High level of this gas is
major cause of lung cancer. I had our house basement
Radon gas level checked and it is well below safety limit
of 200Ml/m3.