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. If you're venting a bathroom fan through an external sidewall, then you'll need a wall mounted bathroom exhaust fan.
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.
For medium-sized bathrooms, use 80 to 99 CFM bath fans. For large bathrooms that are over 100 square feet but under 150 square feet, use over 100 CFM bath fans. For extra-large bathrooms, add 50 CFM for every toilet, 50 CFM for every bathtub or shower and 100 CFM for a jetted bathtub.
Preferable solution is put the vent penetration nearest the bathroom, although usually the side or rear elevation of the house is preferable over the front elevation for cosmetics. Can use sheet metal for all of it, if you prefer, but can use a segment of flex nearest the fan for ease of install or service.
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.
With its smooth inner walls, rigid metal ducting reduces friction making it the most effective choice for a bathroom fan duct. Rigid ducts are low maintenance. They have a long lifespan.
A dehumidifier will work well to keep a bathroom ventilated by sucking in all the humid air from the room and, in return, blowing dry air back into the area. Moisture build-up doesn't stand a chance with a humidifier, making them a fantastic option for many family bathrooms.
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.
The air travels through ductwork that is connected directly to the ceiling vent. Another duct runs from the housing to the exterior of the home, again being, the roof, or overhanging soffit. The blower motor then propels the air from the housing unit through the ductwork connected to the exterior of the home.
Try to install the bathroom air vent between the shower area and the entrance door for best air movement. Take these things into account and when the time comes to install or replace a vent fan in one of your bathrooms, you will be well-prepared to make all the right choices.
Other venting options includes running the duct up through the roof or down through the soffit. Note that the bathroom vent fan must always exhaust to the outdoors; never allow the duct to simply blow into an attic, crawlspace or other enclosed area.
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.
You want to ventilate a bathroom efficiently so place the exhaust fan opposite to ingress (window etc). The most efficient egress (exhaust) is vertically, through ceiling to roof ventilator or eaves vent. Horizontal air exhaust is noisier and less efficient.
This is a sure way to cause blockages that can lead to larger issues.
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.
For example, if you have a small bathroom with only a shower, you may be able to get away with an exhaust fan that is 60-80 CFM. But if you have a large bathroom with a tub, shower, and multiple sinks, you may want an exhaust fan that is closer to 100 CFM or more.
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.
For better performance, duct runs should be as straight as possible. If a bend is necessary, 2 to 3 feet of straight duct should be allowed to run from the fan exhaust port to the first elbow in the duct run.
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 common option for bathroom exhaust fan venting is the ceiling to wall venting option. The second most common is the roof vent installation. The third most common is probably the vertical wall installation.