Let’s think about a typical apartment or condominium building, although this could apply to other buildings as well. Each kitchen and bathroom probably has an exhaust vent to pull the odors and humidity from those rooms out of the building. These vents are served by one or more exhaust fans on the roof which are constantly running. This means that each occupied unit would be under negative air pressure. To make up for that, the building typically will have a makeup air unit introducing outside air to the common hallways. The negative air pressure in the units pulls in the outside makeup air under the doorways. So, every so often, you have a changeout of all of the air in the occupied unit – something you may want to speed up if you’re trying to get rid of airborne pathogens.
Now, imagine what happens if your exhaust ducts are leaking. You may think of leaky ducts as letting air out of the ducts where it’s supposed to go, but in the case of an exhaust duct, the leaks are into the duct from places you don’t care about cleaning out – spaces between walls, chases containing the vents, attics, etc. The leaks render the exhaust fan less efficient – possibly much less efficient – at clearing out the “old” air and creating negative pressure in the occupied space.
Now, add leaky makeup air ducts to that scenario. This is supply air, so in this case the air is leaking out of the ducts before it gets where it’s supposed to go, namely the hallway. So there is less positive pressure in the hallway than there should be given the energy being invested. In more extreme cases, the air pressure could actually be the opposite of what it’s supposed to be. That’s why smelling what’s cooking from the hallway is an indicator of a particularly bad duct leak situation, although you can still have a significant problem even if it’s not bad enough to let you smell Mrs. Anderson’s rhubarb pie.
We recently dealt with a situation like this in a five-story apartment building with about 60 units, which was built in 1990 – not a terribly old building. It turned out that the makeup air ductwork was leaking at a rate of 795 cubic feet per minute (CFM), and the 13 exhaust risers were collectively leaking 5,879 CFM, an average of 452 CFM per riser.
Airways applied the Aeroseal duct sealing technology to the makeup air and exhaust ductwork. We were able to cut the leakage in the exhaust risers by over 96%, from 5,879 CFM to 222 CFM. The makeup air leakage dropped by over 93%, from 795 CFM to only 52 CFM. This meant a dramatic increase in the effectiveness of the exhaust and makeup air fans in circulating air out of and into the building.
Call us at 630-595-4242 if you’d like more information.