any good way to convert attic furnace fan to whole house fan

[old dirtbeard]

Hi all,

We have a newer two-speed attic furnace/HVAC unit which currently draws the intake from a hallway ceiling vent right next to where I would like to install a whole house fan to vent warm air into the attic to cool the house in the summer evenings rather than run the AC.

I thought that we could use the existing two-speed furnace/AC blower to just divert the incoming air into the attic and have it double as a whole house fan. I think it would require some diverter valve to send the air into the attic rather than back through the plenum to return to the house, but this would obviate the need to cut new holes in the ceiling, install and wire a whole house fan, open up more ceiling space to heating and cooling losses, etc.

Clearly it may be more work than it is worth, but I was wondering if anybody has tried something like this.

We live in SoCal near the coast, so we have cool evenings regardless of the temperature during the day, and it makes a whole house fan an attractive option, particularly since we have a 5 ton AC unit with 169 LRA at 240 VAC (clearly oversized for our needs).

Thank you,

OD

[Bob F]

One problem would be that all the dust in the air you exhaust would be going through the furnace, dirtying the heat exchangers and/or the filters. It would be better to duck off the duct to the furnace for a separate fan, but that would require a way to block the flow to/from the furnace to prevent backflow.

I have considered how I could duct outside air to the furnace intake for similar results. with the outside air being filtered on the way into the house - a much more desirable result. Some kind of controllable duct to a gable vent could make this possible in your situation. Air would come from the inside, or the outside gable vent.