Furnaces should not exhaust ANY pollutants in your home. If they are, there's a crack or leak somewhere and they should be immediately shutoff and serviced. At

Furnaces should not exhaust ANY pollutants in your home. If they are, there's a crack or leak somewhere and they should be immediately shutoff and serviced. At no point the gas exhaust should mix with indoor air. I don't know about gas dryers but it would be surprising if they were any different.