A 30-plus-story hotel had four separate kitchen exhaust systems that all discharged through a mechanical-room wall just above the fifth-floor low roof. The hotel had been getting complaints about cooking odors in the seventh-floor conference rooms.

The rooms were conditioned by high-rise fan-coil units with no outside-air (OA) connections. The windows did not open, and I did not feel air movement around them. There was OA ventilation to the corridor, but it was from the same system that fed the guest-room corridors. If the corridor system was the source, odors would have appeared on every floor.

Odorous OA might have been drawn in by stack effect, but odors had occurred even during hot weather, when the air conditioning would have reversed any stack effect, making air flow out at the seventh floor, not in. There seemed to be no way the kitchen-exhaust odors could be coming back into these conference rooms. Then I thought, β€œMaybe they aren't leaving the building at all.”

The four kitchen-exhaust fans were near the outside wall, where there was no doubt about cooking odors. The hotel's engineer confirmed that odors were a regular occurrence. At least one of the systems was leaking kitchen exhaust inside of the building, but which one? How could I be sure?

β€œCan we get a chef to saute some garlic in each kitchen, one at a time?” I asked.

This process started in the first-floor kitchen as we waited in the mechanical room. No odors were detected. We stepped out onto the fifth-floor roof, and the odor was strong. The second-floor kitchen was next. Again, no odor was present in the mechanical room, but a smell could be detected on the roof. I was beginning to wonder if this was such a great test.

The chef then went to the third-floor kitchen, and an odor filled the mechanical room. The third-floor kitchen system was the culprit, but we tested the fourth-floor kitchen anyway. It is a good thing we did. Once the odor from the third floor cleared, we gave the chef the go-ahead. Garlic odor soon followed. Now, we were sure the odors were leaking from the ductwork, and we knew from which ducts the smells were coming. Sure enough, later careful examination found leaks. Sealing the ducts contained the odors.
David M. Elovitz, PE
Energy Economics Inc.
Natick, Mass
.