Bathroom fan installation requires outside ventilation. If the bathroom exhaust fan or venting fan isn't accessible through an attic, you'll need to vent through a sidewall of your house.
Venting through the ceiling is better than the wall. Venting through the wall exposes soffits, eaves, and whatever your wall material is to hot, moist air. Venting through the ceiling, the air rises straight up.
They extend through the roof to allow sewer gases to escape from your home safely. Without proper venting, these gases can build up inside your home, leading to foul odors, health hazards, and even dangerous levels of methane gas.
The moist air will fuel the growth of mold and mildew on the roof framing and the sheathing that covers the timbers. Wood rot is an absolute certainty over time if you dump bath exhaust into an attic. This moist air must exhaust to the exterior of your home. This is non-negotiable.
To fulfill the local exhaust airflow requirements of ASHRAE 62.2 (2010) and the International Residential Code (IRC 2021, Section M1507), bathroom fans should have a mechanical exhaust capacity of ≥ 50 cfm for intermittent operation or ≥ 20 cfm of ventilation when operated continuously.
You can attach a wall mounted bathroom exhaust fan to an external wall in a bathroom. This type of fan pulls the air out of the bathroom, through the ducting and outside via the external wall of your home.
Using a Floor Duct Vent
In bathrooms without outside access, duct vents can be used to ventilate bathrooms if ceiling venting is not possible. A floor duct vent is a special machine that uses floor grates to remove moisture and bad air from your bathroom.
Ceiling-mounted vents must be routed through the ductwork in your roof to an external exhaust pipe or have special ductwork installed to accommodate them. Whatever you do, ensure that no air is getting ventilated directly into your attic, as this can cause mold and mildew buildup over time.
Yes, the toilet and sink can share the same vent, as can the shower. It's common to have one main vent pipe for multiple fixtures, although you might need a larger pipe. You should check with local building and plumbing codes to confirm you'll have adequate piping for your home.
Q: Is there a height requirement for plumbing vent pipes above the roof? A: A vent pipe must extend above the roof as local building codes dictate, typically at least 12 inches, to prevent clogs from debris.
Do bathrooms need to be vented through the roof? Not necessarily. If the bathroom is in a lower floor or the basement, it's easier to vent the fan through a side wall. In such cases, a wall-mount fan usually makes more sense than a ceiling-mount.
When drain lines aren't properly vented, low pressure inside the pipe can suck water out of the traps, letting sewer gas in. Air pressure imbalances inside the drain pipe can restrict water flow and cause sluggish draining, often mimicking a partial clog inside the pipe.
Summarized, if you install a window in the bathroom, it must be at least 3 square feet in area. This window only needs to be able to open halfway, meaning the total open window space only needs to be 1 1/2 square feet. Open windows can provide highly effective ventilation in bathrooms without showers or tubs.
Behind or within the Wall: In most cases, the vent pipe for a toilet should run vertically from the toilet's waste pipe (known as the closet bend) and extend upward to connect with the main vent stack or a branch vent line that ultimately exits through the roof of your home.
Plumbing the Bathroom
The most common configuration is to feed 2" PVC down from the ceiling within the wall behind the toilet. The vent pipe connects into the toilet drain pipe. The sink drain pipe and the tub/shower drain pipe are vented with 1.5" pipe that branches off from the 2" PVC mainline.
The best solution is to vent the bath fan directly through the roof. In this article and the video above, we'll explore the step-by-step process of installing a roof-mounted bath fan vent, as demonstrated by This Old House general contractor, Tom Silva.
All plumbing in your home must have vents to remove sewer gasses and regulate air pressure in pipes. When liquid goes down a pipe, air needs to follow it. Without the vent pipe, the liquid will attempt to draw air through the P-traps on your tub or sink. This will create a gurgling sound.
Choose a fan that can ventilate at least 1 CFM per square foot of room. So, for an 80 square foot bathroom, select an 80 CFM fan. For bathrooms 50 square feet and smaller, it's recommended you purchase a bath fan designed for small rooms. In other words, choose under 79 CFM bath fans.
In general, the vent should be as close as possible to the fixtures it serves. This proximity helps ensure the vent can effectively equalize air pressure and prevent sewer gas entry. However, there are some common guidelines to consider: The vent should be within 5 to 6 feet of the fixture drain it serves.