For bathrooms up to 100 square feet in area, HVI recommends that an exhaust fan provide 1 CFM per square foot (approximately eight air changes per hour) to properly ventilate the bathroom.
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.
Aluminum Semi-Rigid Duct
Semi-rigid is a good option for use in high-humidity areas.
You can increase the flowrate of the bathroom fan by making the vent in the door bigger or increasing the power of the bathroom fan.
All these are a factor in choosing your vent fan. If it's just a small bathroom with a toilet and a shower, you may only need a 100 CFM fan. If you have a jetted tub and shower, you will likely need a 200 CFM fan. CFM is a measure of the fan's ability to move air.
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.
This is a sure way to cause blockages that can lead to larger issues.
Install an Exhaust Fan
One of the most common and effective ways to ventilate a bathroom without windows is to install an exhaust fan. Exhaust fans work by pulling stale air out of the bathroom and pushing it outside, replacing it with fresh air.
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.
While many homeowners opt for the easier route of venting into the attic or soffit, this can lead to mold growth and other problems. The best solution is to vent the bath fan directly through the roof.
Keep the doors open. Keeping the bathroom door open after using the bathroom is a great way to help ventilate the bathroom if there aren't any windows. This lets out any steam that has built up when you were taking a shower or a bath.
We recommend at least an 80 CFM for most bathrooms but a 100/110 for a larger master bathroom. This will help move the moisture out of the bathroom and reduce the risk of mold.
Keeping your shower doors closed at all hours of the day locks in moist air and can lead to mold. After you shower, the interior space is at its wettest point. Try to keep the doors open for a half hour or so until the steam clears. If you have a fan in your bathroom, make sure to turn it on and let the air circulate.
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.
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.
Surprisingly, some building codes do not require bathroom fans. All municipalities have different requirements, but some do not draw a hard line on requiring exhaust fans. Bathroom ventilation is needed in those areas, but it can be from a window or fan—you choose.
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.
Ventilation rates based upon eight air changes per hour are generally suggested. For most bathrooms this works out to one CFM per square foot of bathroom area. For example, a 7' x 10' bathroom would require a 70 CFM fan. A 50 CFM rating is recommended as a minimum for bathrooms 50 sq.
The most popular venting option for a bathroom exhaust fan is a pipe extending vertically through the roof. This choice only works on home designs that allow a straight vertical pipe with no bends. It's the most efficient means of pulling moisture out with the least chance of moisture re-entering the home.
A fan that is too big can cause a bathroom to be cold and noisy. This is why calculating the correct CFM is important.
To adjust the CFM, you can change the speed of the blower or alter the ductwork size. Increasing the blower speed won't have much effect if a room's duct is too narrow. A 12' x 12' foot room is 144 square feet. You generally need at least 1 CFM per square foot, meaning that room's duct should have a 144 CFM capacity.
On the other hand, if your CFM is too high for your room size, it can cause ventilation problems. Too much air results in too little ventilation, which in turn causes high humidity. The excess moisture in the air can then lead to mold and mildew, as well as other problems.