I recently bought a newly (and poorly) gut renovated townhouse where each floor has its own independently zoned thermostat. Throughout the summer whenever it's gotten above 80 degrees, I've been having a massive condensation problem on the top floor of the house. The top floor's hallway air vent is directly next to the stairs that lead up to the rooftop bulkhead, and these stairs and the bulkhead aren't included in the HVAC system. As such I think what's happening is the cold air from the top floor is meeting the hot air from the roof stairs, which is creating a ton of condensation. The vent is constantly dripping water and the ceiling around the vent is wet and starting to mold. I've been trying to wipe it all down with a towel multiple times a day, but this obviously isn't sustainable or working particularly well.

How can I remedy this?

view up the stairs with moisture-damaged vent

close up view of vent and moisture damage

1 Answer 1


Air circulation problem

Hot an Humid air resizes, in your case it ends up in the pocket at the top of the stairs with nowhere to go.

The air vent next to the stairs blows cold air. When the hot/humid air reaches it it will condensate and form drops.

Unfortunately the air return is further away from the action, which would suck up the hot/humid air to the heat exchanger coil and remove the humidity.

Possible fix, install a fan at the top of the stairs, to distribute the hot/humid air.

More complicated fix, instal air return duct at the top of the stairs.

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