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wrote:
The house is supposidly air tight so a duct was installed from the
outside of the house to the interior closet that has the furnace. In
the winter the duct stays shut unless the furnace turns on. However, it
is wired to override the valve that shuts the flap with a toggle switch
so that the duct will remain open all the time, so that in the summer,
the theory goes, I can use the fan on the furnace to pull fresh cooler
air in. It doesn't work that great.

It's still unclear how this is set up. If the outside air duct just
runs into the furnace closet, it sounds like it is there to supply
combustion air for the furnace. It would have to be connected into
the return air ducts for the blower to draw in air. And if it is
hooked up the latter way, it's a big mistake, as you are drawing cold
air into the house and wasting energy. The correct way of doing this
is to use a heat exchanger, so the outgoing air gives up most of it's
energy to the incoming air. And very few homes have them because most
get sufficient air intake through leaks, doors opening, etc.

The whole house fan in my brother's place is in the ceiling of his
hallway and pushes household air into the attic space. Cooler night air
is pulled in, I guess, cooling the house very nicely.

I am wondering if putting a fan in the duct to pull air through the
registers out through that duct will work like the whole house fan, or
if somehow this system can be modified to remove warm air from the
house in order to pull cooler air into the house through open windows.
Unless there is a breeze, the cooler outside air doesn't cool the
inside of the house that great and the summer fan doesn't add enough
fresh air to make much of a difference. Will rigging it to work the
other way, pushing warm air out work better?

It seems like box fans and attic fans are wired to pull the hot air out
of spaces and the cooler air is pulled in, passively so to speak.