What is this vent?

[89th]

This is on the back of my house above the basement doors, I obviously presume it’s an intake/output vent system of some sort (the left circle vent is clogged, I presume from years of collecting dust). Anyone know?

There are two circle vents under the aluminum hood.

Inside the house this vent aligns just above our basement ceiling.

[Renauda]

@89th

My guess would be bathroom fan or clothes dryer outtakes. Have never seen a configuration like that on a house. What do have in your basement that requires outdoor venting?

[Mik]

With the fluff on it, it's likely the dryer vent. It could be water heater or furnace too. If they are gas they require venting. What is on the first floor? Where does your range hood, if you have one, vent to?

[George K]

What @Renauda said. We had a similar hide-away for wasps, etc at the Cheddarshack. It was right by the laundry room.

[89th]

Mysterie solved.

The right circle leads to an open vent in the utility room, which is a "combustion air duct". Basically a passive way to bring air into the house to replace air that is lost (via furnace, bathroom vents, etc).

The left circle (that I just cleaned off, probably hasn't been cleaned since the house was built in 2005), is the cold air intake for the Heat Recovery Ventilation (HRV) system. The HRV is used when the heat is on to bring in fresh air during the winter, mix it with the humid/stale air from the house. The "output" duct for the HRV was on the other side of the house, so I didn't think this duct would also be involved but I was able to trace the duct enough to see.

[89th]