Today’s post is about the various exhaust vents in your home.
There are a multitude of exhaust vents in most homes. At this point I am not going to discuss combustion appliance vents/chimneys. This post is about bathroom, laundry, kitchen, dryer, and whole house exhaust vents—-mechanical type vents—-and specifically—-just the vent caps for this equipment.
Because of their importance in helping control humidity levels and indoor air quality it is critical in modern homes that these vents be maintained as functional as possible. While it is important for all aspects of these mechanical ventilation fans to be properly maintained, today I am only going to talk about the exterior cap.
All exhaust fans should be vented to the exterior of the home at a cap with a back-draft damper.
These caps can be on the side walls of your home or on the roof and sometimes even on the soffits (although soffit determination should be avoided if at all possible).
I recommend that you turn on all of your exhaust fans and walk around the exterior of your home and make sure that the flaps are opening properly. If they are on your roof you may need to use binoculars. Wasps and other critters like to build their nests in these caps and the winter time is a good time to make sure nests and other debris is not present. But be careful, stinging insects may be present. Wasp’s nests can fill the cap so that the vent flap will not open. Remember too—-roofs can be DANGEROUS places so make sure whoever maintains the caps knows what they are doing.
Caps can suffer mechanical damage to the point that they will not open properly and screens can become clogged with lint and debris. If the flap moves freely by hand but no air is coming out when the fan is running or the damper does not open when the fan is running—–have the venting fixed by a qualified person—-it may be venting warm moist air into areas that could cause damage to the home.
These exhaust fans should never terminate in crawl spaces or attics or at roof and soffit vent screens. Especially problematic are the types of terminations in the next two pictures.
Obviously—unless you are creating a bird house—-the flap must be able to close by gravity if you are going to keep cold air and vermin out of the ductwork.
Many of these vent caps come with screens and/or protective grilles—and most of these screens are required by the building codes. While these screens may prevent small birds and mice from building nests in them, they are of questionable value in my opinion. But since they are required by the codes we must make sure they are maintained free of debris and vermin. Properly screened vents actually will promote wasps because they are protected from other vermin behind the screens and if the screens had smaller openings they would clog up even more quickly.
Because screens are required in the caps of range hood vents, we must be especially vigilant in maintaining the screens in these caps clean. Depending on cooking habits these screens are prone to plugging with grease and lint, creating a fire hazard.
Screens also should NEVER be installed on dryer vents because when they become clogged, the lint represents a fire hazard, and it will take forever to dry your laundry—-wasting a lot of energy.
Louver type vent caps often don’t operate well, the flaps sometimes don’t fully open and sometimes they become warped by the sun—-when installed on the sunny side of the home. I prefer single flap type caps for most vents. Most louver type caps also do not meet the requirement for there to be a screen—when they are used at locations that require a screen.
Here is a list of some of the many things that can be wrong, or go wrong, with just this single component of your exhaust vent systems.
- Wrong type
- Mechanical damage
- Blocked with lint/debris
- Blocked by nests (wasps and other vermin)
- Damper painted shut
- Too close to the ground
- Not attached
- Not sealed to prevent moisture and vermin entry to the home
- Vent flap stuck open
- Vent flap stuck closed
- Vent screens/grilles in caps that should not be screened
- Missing back draft damper
- Damaged back draft damper
- Damaged louvers
- Missing louvers
- Installed at wrong angle—damper won’t stay closed
I am done venting now.
By Charles Buell, Real Estate Inspections in Seattle
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