Apartment & Multifamily Duct Sealing in San Jose: Fix Leaky Exhaust Risers With Tenants in Place

Key Takeaways

1. What Leaks in an Apartment Building

Most multifamily buildings in the Bay Area have some mix of three duct systems. Each can leak, and each causes different complaints.

• Central exhaust risers. Vertical shafts that pull air from kitchens and bathrooms on every floor up to a roof fan.
• Central supply or ventilation systems. Corridor air and fresh-air systems serving many units from one air handler.
• In-unit systems. A furnace, fan coil or heat pump in each apartment, with ducts in soffits, ceilings or attics.

Our multifamily ductwork services in San Jose start by figuring out which systems your building has and which ones are behind the complaints.

2. Exhaust Risers: The Leak You Can't See

A central exhaust riser is designed to pull a set amount of air from each kitchen and bathroom grille. When the shaft leaks, the roof fan pulls part of its air from wall cavities and ceiling spaces instead. A NYSERDA study by Steven Winter Associates found typical leakage points where the shaft meets the roof curb, at joints in the vertical shaft and at the connection between exhaust ducts and grilles.

Because these leaks are inside walls, finding and sealing them by hand usually means opening finished surfaces in occupied units. Aeroseal works from inside the shaft, so the sealant finds the leaks for you. Learn more on our exhaust shaft sealing page.

3. Odor, Smoke and Noise Complaints Between Units

Cooking smells, cigarette or cannabis smoke and musty air moving from one apartment to another are among the hardest complaints to resolve. In Aeroseal case studies of apartment buildings, odors transferring between units were listed among the problems before exhaust risers were sealed.

The NYSERDA study also notes that when exhaust fans run on timers, shafts can become passive paths for moving contaminants between units. Sealing riser leaks and keeping fans running as designed reduces those air paths.

Noise is different. Sound travels through walls, floors and shaft construction, and duct sealing is not a soundproofing fix. If noise is the main complaint, we'll tell you so.

4. Unit Turnover and Comfort Complaints

Turnover is a good time to look at ductwork. A vacant unit gives easy access to grilles and in-unit equipment, and fixing comfort problems before a new tenant moves in avoids repeat service calls. Aeroseal's multifamily article describes duct leakage as a cause of uneven unit temperatures and reduced tenant comfort.

Common signs at turnover:

• Bedrooms that run hot or cold compared with the living room
• Weak airflow at one or two registers
• Mold or mildew in a bathroom with a weak exhaust fan
• Repeated thermostat or equipment service calls

For in-unit systems, we test leakage and airflow at every register much like a home. See duct leakage testing.

5. Ventilation Performance

Exhaust and fresh-air systems exist to keep indoor air healthy. If some units are under-ventilated, moisture and pollutants build up. If others are over-ventilated, you pay to heat and cool air you throw away. The NYSERDA study notes that under-ventilation in parts of a building can harm indoor air quality.

In an Aeroseal case study of a New York high-rise, no tested apartments were within the intended exhaust airflow range before the work. Afterward, Aeroseal reports 100% of kitchens and 98% of bathrooms were within target. That project also included other ventilation work, so results like these depend on the full scope. Tightening the ductwork gives balancing a reliable starting point. Learn more about air quality and ducts.

6. Energy and Utility Costs: Who Pays

Who benefits from lower energy use depends on how your building is metered.

Even when tenants pay their own bills, comfort complaints, service calls and vacancy affect your income. Aeroseal's multifamily article reports one project where duct leakage fell more than 90% and HVAC-related energy costs dropped 20%. Results vary by building. See lower energy bills.

7. Working With Tenants in Place

Aeroseal reports multifamily sealing can be done without opening walls or disrupting tenants. Exhaust risers are often sealed from the roof, with short visits inside units to remove and block grilles.

Our Typical Multifamily Sealing Process

1. Site assessment. We review drawings, walk the roof and sample units, and measure leakage and airflow where possible.
2. Tenant notice. We give you a schedule and notice language for the units on each riser.
3. Prep. Grilles on the riser are removed and openings are temporarily blocked. Large gaps are repaired by hand.
4. Sealing. Sealing equipment connects at the roof fan curb or another access point, and a computer tracks leakage as it drops.
5. Restore and test. Grilles go back, the fan is reconnected and final readings are taken.
6. Report. You receive before and after results for each riser or system.

8. Repair First, Then Seal

Aeroseal seals holes up to about 5/8 inch. Disconnected ducts, crushed sections, missing grille boots and damaged fan curbs need hand repair first. That's the multifamily ductwork repair part of our San Jose work. Repairs use mastic or UL-181 foil tape, which ENERGY STAR recommends over cloth duct tape.

We'll also flag issues outside sealing, such as worn fans, stuck dampers or grease ducts, so you can route them to the right trade. See how we repair ducts.