Where Does Vent Air Go In an Apartment?

Most people flick on the bath fan without giving air movement a second thought–unless the fan does not work. But you should; because it can affect people’s health.

The IRC (International Residential Code) states that extraction fans must vent outside the building. They can be attached to HVAC systems or vented individually. Unfortunately, earlier building codes allowed fans to be vented into attics, which can lead to mold and/or odors.

Apartment renters often lack the leverage to effect building repairs. But health and safety issues may help focus attention on problems.

Hopefully, our suggestions and information will help pinpoint any problems you may have.

Apartment Air Vents are Usually Connected

Generally, apartment ventilation fans share a common vent shaft–somewhat like the bathroom fan systems used in hotels. Each one is–or should be–fitted with an air-tight damper to prevent odors from traveling between living units.

Good backdraft dampers will use rubber seals that prevent air and odors from passing between units. If you are smelling strange odors like cigarette smoke, cooking smells, or something even worse, damper replacement is your easiest and least expensive fix.

Courtesy: Amazon – AC Infinity Backdraft Seal

Apartment buildings are designed to make the best use of available space. Meaning that quite often bathrooms and kitchens will be positioned back to back to avail themselves of the central air shaft. (Right-hand picture below.)

Well-sealing backdraft dampers that keep out odor will also help with soundproofing. Which, in some cases, could be very important.

Courtesy: Minnesota Department of Commerce

Individual Apartment Ventilation

Occasionally apartment fans will be vented individually. Piping is often run through the floor framing and you see rows of galvanized vent hoods on the outside of buildings. Not cute but effective.

Individual venting does not require backdraft seals. Each hood vent is equipped with a flapper inside the hood. Air pressure opens it up when the fan is on. Gravity keeps it closed when no air is flowing out.

MURB Ventilation Systems

When someone mentions an apartment building, many of us think of a three or four-story walk-up (as pictured above). But many Multi Unit Residential Buildings (MURBs) are middle-rise to high-rise units. Almost all of these built in the last 60 years use mechanical HVAC ventilation systems.

Hot air rises, but your average bathroom fan is not going to move bathroom air 20 or 30 stories, or more. The Heating, Ventilation, and Air Conditioning (HVAC) system is designed to make living comfortable, safe, and relatively easy.

Large motors hooked up to heating units and air conditioning units move warm or cool air where needed inside the building and vent excess air out of the building.

Venting Air Outside the Building

As mentioned before, all ventilation should be routed outside the building. Bathroom fans and kitchen fans are usually moving moist odorous air. Venting into the attic, crawl space, or another room can cause serious problems.

  • Moisture Build Up. Moisture-laden air can make insulation wet and less effective. In cold climates, too much moisture can freeze in the attic.
  • Ice Dams. In cold climates, venting warm moist air into an attic can cause ice dams. The excess heat inside the attic will melt snow on the roof. When it refreezes, ice builds up along the roof edge. Which can cause leaks and damage.
  • Mold. Wet wood and insulation promote the growth of mold and rot. Not only will these stink, but black mold can be a serious health problem. Rot and mold can also shorten the lifespan of a building.
  • Odor. Odor can seep back into the living area.

All venting ducts are supposed to protrude through the roof, through the wall, or through the soffit. According to the International Residential Code (IRC), no vent can be within 10 feet of a ventilation intake. It also has to be at least 3 feet away from windows, doors, and furnace intakes.

Roof-mounted ventilation is usually preferable–especially on flat-roofed buildings. The exhaust is almost always away from air intakes, windows, and doors. The units are also easier to work on.

Note: I am not a big fan of venting ducts through the soffit. The chance of warm moist air being sucked back into the attic is very real–especially on a windy day.

Buying an Apartment or Condo

The average time a home buyer spends looking at her/his new place is 20 minutes. With all of the old rental buildings being turned into condos, spend a little time considering the ventilation system of your potential purchase.

Make sure it works, is hooked up, or even exists. It is probably well worth the investment to hire a good home inspector. It is a bonus to find one with knowledge about HVAC systems. Someone who knows a bit about CFM requirements and pipe sizes. You don’t want to buy a place only to be presented with a whacking big repair bill.

End Notes

A couple of final thoughts about codes and venting.

International Residential Code

The IRC has been adopted by 49 states. But keep in mind that it is usually considered the minimum standard. Most localities have additional building codes that take precedence over the IRC. Local codes usually take into consideration things like weather conditions, soil conditions, etc.

Yes, You Should Have Ventilation

If you cannot open a window in your bathroom or kitchen, you should have fans to remove wet warm air. You will be preventing damage, mold, and excess dirt accumulation. If you are getting fog on mirrors and windows, there will be a thin layer on most everything else.

Although far from the best choice, you can install a non-venting recirculating fan. It will at least move air around the room and remove some of the moisture.

Where Does Vent Air Go In an Apartment?
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