In a multifamily building, one tenant’s air can become another’s. Shared shafts, corridors and exhaust systems carry smells, smoke and moisture between units. This guide is for property managers of buildings with central systems, and covers the common problems and how to address them.
How air moves between units
| Pathway | What it causes | Fix |
|---|---|---|
| Shared exhaust shafts | Odors and smoke traveling between units, or back-drafting | Balance exhaust, check fan operation and seal shaft openings |
| Corridor air supply | Corridors pressurized unevenly, pushing air into units or pulling it out | Balance corridor supply and check door gaps |
| Unit leakage | Air passing through walls, floors and penetrations | Air sealing at penetrations and unit separations |
| Kitchen and bath exhaust | Cooking odors, humidity and mold in bathrooms | Verify exhaust airflow in each unit and keep makeup air available |
| Trash chutes and utility rooms | Odors spread to adjacent areas | Exhaust and sealing at the source |
A method for investigating complaints
- Log complaints by unit, time and type: odor, smoke, humidity or noise.
- Map them. Units stacked in a line suggest a shaft problem, and corridor-side units suggest a corridor pressure problem.
- Check the rooftop exhaust fans and the corridor supply units.
- Measure exhaust airflow at the affected units and compare with design.
- Check that makeup air is available, so exhaust can move air.
- Make one repair, then re-check airflow and the complaint log.
Why balancing matters
Central exhaust systems serve many units with one fan, so a small imbalance affects many people. Measured exhaust airflow at each unit shows who is over-served and who is under-served. A balance corrects it and gives you a record. See what a balance involves and how to troubleshoot problems in large buildings.
Policies that help
- Clear rules on smoking and cooking practices, as local law and leases allow.
- A standard way to report air quality problems, with a response time.
- Annual checks of roof exhaust fans and corridor supply.
- Filters changed on schedule in common air handlers.
Common mistakes
- Treating each complaint alone. The pattern points to the cause.
- Blocking a leaking grille. It moves the problem.
- Ignoring bathroom exhaust. Moisture builds up and mold follows.
Questions property managers ask about multifamily IAQ
Who is responsible when odor moves between units?
It depends on the cause and the lease. Start with the building systems, since many cases trace to exhaust or pressure.
Can tenants fix it themselves?
Not usually. They can report accurately, but the shafts and fans are building systems.
How often should exhaust be tested?
After repairs and on a regular cycle, such as every few years or when complaints appear.
A worked example: kitchen exhaust and makeup air
A building has a central roof fan that exhausts kitchens and bathrooms in forty units. After a renovation sealed the corridors more tightly, tenants on the upper floors report weak exhaust and cooking odors lingering. Measured exhaust airflow at the upper units is far below design, and the corridor makeup air is lower than before. The cause is a lack of makeup air, so the fan cannot pull what it should. The fixes are to restore corridor supply, rebalance the exhaust risers and confirm the readings at each unit. The scenario is illustrative, but missing makeup air is a common cause of weak exhaust in tight buildings.
To test exhaust and corridor airflow, call Ghazi Hussain at (908) 323-9780 for a quote.
