Pim from Etobicoke would like to install a door from his garage into the house. The danger of this is that it opens a path for pollutants from the car into the living space of the house. Recent CMHC/Health Canada research has shown that many more pollutants than we imagine come off of cars and find their way right through the walls into the house, particularly dangerous gasses from hot breaks and the hot motor.
The danger from these gasses in any attached garage could be mitigated if we exhausted air out of the garage for a while after the car entered or left, creating a negative pressure with respect to the house and preventing the gasses from moving into the living space.
Our TV crew came up with a nifty solution. An inexpensive bathroom exhaust fan, plugged into a motion sensor outdoor light fixture with a built in 10 to 20 minute on timer. Anyone moves in the garage and the light comes on in one light socket, a good idea in any garage, and the other socket has a screwed-in plug cheater that activates the exhaust fan. Both the light and the fan go off 10 to 20 minutes later. But check that the fixture is capable of taking the fan motor load.
CMHC has a research report on air pollution and attached garages.