Water dripped from the windows and mold grew on the walls of a series of upscale urban condominiums. Other experts had ruled out water leakage. I arranged to visit several units.

As we rode the elevators in the residential tower, the facility manager told me about the building's systems.

"We have a state-of-the-art corridor ventilation system," he said. "It has a total-energy-recovery wheel—sucks the heat right out of the exhaust and puts it back into the makeup air. Saves us a ton of money on heat."

This sounded like a clue. When we stepped into the corridor, I noticed two air grilles: One was for supply; I asked about the other.

"Is this the exhaust grille for the corridor ventilation system?

"Yeah," the facility manager said. "I know it's close to the supply, but this is an old building, and that's the only place we could fit it in."

Another clue. Entering one of the condos, I felt the high humidity wash over me. No wonder they had mold on the walls! Humid air hitting cold walls and windows would condense just like the "sweat" on cold drinks.

I checked the bathroom: No exhaust. (When the building was built, exhaust was not required if a bathroom had windows.) Then I saw a stacked washer/dryer. The "condensing" dryer did not exhaust to the outdoors. Measurements confirmed my suspicions: The dryer may have condensed some of the moisture from the laundry, but it released moisture into the air. I had seen enough.

"The condo units generate a lot of moisture, but there is no ventilation to flush this moisture," I said. "The corridor system moves a lot of air, but with both supply and exhaust in the corridors, none of it gets into the units. Worse, the 'energy-recovery' system recovers not only heat, but moisture. About 80 percent of the moisture exhausted from the corridors comes back via supply air.

"I'm afraid we need to shut off the heat-recovery system and only provide supply air to the corridors. By not exhausting the corridor, the system will pressurize it slightly, forcing dry air into the apartments and flushing the moisture."

Gary Elovitz
Energy Economics Inc.
Newton Centre, Mass.