Is this a "whole house fan" / how is it controlled?

Question

Hi,

Question about a new-to-us home (primary residence, 2-story SFR).

With summer rolling around here in WA - I was curious about that fan that sits behind a register in the ceiling of our upstairs hallway - and I cannot figure it out for the life of me.

House was built in 1993 and there is no switch to be found. Tried to trace the wire in the attic - but would need to dig up insulation to follow it. Talked to an original owner neighbor, they mentioned they had the same and it would come on by itself somehow but they didn't know what triggered it.

Before digging through our attic - I figured I'd ask here...

Could this be part of the overall heating system (gas furnace / forced air)? Is there some other sensor somewhere in the house that might be triggering this?

Is this a "whole house fan" or something else?

The fan itself is a radial EBM Papst fan, it has four wires connected to the unit and just a regular romex connecting to the unit based on what I could see. It's enclosed by a box in the attic and vented through the roof.

Would appreciate any pointers!

Thanks!

David Lee Hall, III · Answer

Go over to Reddit and post these pictures and description on r/Whatisthis/ - you should have an answer in about an hour - probably by either an engineer or sales rep or home builder that dealt with the things daily 30 years ago. :-)

Jonathan Stone · Answer

Very tough to tell from the pictures.  There are a few ways Whole House Fans can be run.  Typically they are attached to a light switch style disconnect and they can also have 1 or 2 thermostats wired to them.  This can mean if you power it on and the outside is cooler than the ceiling temp they run otherwise they are off.  Also if this is original equipment either the sensors or the fan likely need maintenance or replacement after 30 years.  Wish I could help more.