Most new homes are built with
forced-air heating systems. So it's no
wonder that some builders use the
ductwork for fresh air ventilation as
well.
Besides bringing fresh air into the
house, integrating ventilation into a
existing forced-air system can actually
correct a problem that's common to
tight homes with combustion appliances.
It's called backdrafting and it
works like this: When a house can't
get enough outside air to replace that
removed by exhaust-only appliances
like clothes dryers and bath fans,
then the interior is put under a negative
pressure. To equalize the pressure,
air is pulled down the chimney
and through the furnace. If the
furnace happens to be turned on, this
can also introduce potentially lethal
carbon monoxide into