Considering that the exhaust from a dwelling unit is not considered to be hazardous or noxious and is of low volume, the 3-foot (914 mm) separation from windows is deemed to be reasonable.
Section R303.
When a community adopts this section, it essentially says that bathrooms must have open windows for venting purposes. The code reads that the window must have an "aggregate glazing area...of not less than 3 square feet (0.3 m2), one-half of which must be openable."
Each vent shall terminate not less than 10 feet (3048 mm) from, or not less than 3 feet (914 mm) above, an openable window, door, opening, air intake, or vent shaft, or not less than 3 feet (914 mm) in every direction from a lot line, alley and street excepted.
A fan should always be sited in the furthest window or wall from the main source of air replacement to avoid short-circuiting the airflow. It should be located as high as possible in the window or wall nearest to smells or steam, but not directly above eye-level grills or cooker hoods.
To bring cooler air from outside, place the fan near an open window screen or door. The air should blow into the room. To take hot air out of the room, face the front of the fan towards an open window screen or door. The air should blow out of the room.
The exact distance will depend on the size of your home but, generally, the regulations prevent a boiler flue from being situated within 30-60cm of a window or door. This is to prevent harmful gases from exiting the flue and then re-entering the property through an open door or window.
It's typically recommended that you go with a 2" PVC pipe for the vent. This is according to the uniform plumbing code (UPC). It may not be enough, depending on how many fixtures you are trying to run off the vent. You should check with local building code requirements to be on the safe side.
Placing the heat vents beneath the windows is actually best for efficiency and proper airflow. Essentially, you want to target your warm air where the home is cold.
Considering that the exhaust from a dwelling unit is not considered to be hazardous or noxious and is of low volume, the 3-foot (914 mm) separation from windows is deemed to be reasonable.
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.
Window Fans
Typically the other walls of the bathroom are all internal leaving no obvious way to duct to the outside world. Window Fans solve this problem by mounting directly into the glass. This can be a tricky job that should only be undertaken by a professional electrician.
A mechanical draft venting system, excluding direct-vent appliances, shall terminate at least 4 feet (1219 mm) below, 4 feet (1219 mm) horizontally from, or 1 foot (305 mm) above any door, operable window or gravity air inlet into any building.
Locate the exhaust terminal at least 3 feet from any door or window and away from the fresh air intake of a high-efficiency furnace, water heater, or any other HVAC intake. It should also be located away from air conditioning or heat pump condensing units installed outside. Avoid terminating the duct at the roof.
For a 1 ½-inc pipe the vent should be 42 inches away at the most while a 2-inch pipe must have a maximum distance of 5 feet. For pipes that have a diameter of 3 inches the distance is 6 feet and for a 4-inch pipe the most it should be away from the vent is 10 feet.
The Home Ventilating Institute (HVI) recommends that exhaust fans for bathrooms up to 100 square feet provide 1 CFM per square foot. For bathrooms over 100 square feet, HVI recommends basing ventilation on the number of fixtures—50 CFM each for the toilet, shower, and tub, or 100 CFM for a jetted tub.
An open vent terminal from a drainage system shall not be located directly beneath any door, openable window, or other air intake opening of the building or of an adjacent building, and any such vent terminal shall not be within 10 feet (3048 mm) horizontally of such an opening unless it is 3 feet (914 mm) or more ...
No vent terminal shall be located directly beneath any door, window, or other ventilating opening of a building or of another building, nor shall any such vent terminal be within 10 feet horizontally of such opening unless it is at least 2 feet above the top of such opening.
Liquid fuel normal vent pipes shall terminate outside of buildings in a nonhazardous location at a point not less than 2 feet (609.6 mm) measured vertically or horizontally from any building opening and not less than 2 feet (609.6 mm) nor more than 12 feet (3657.6 mm) above the fill pipe terminal.
Windows: Flues must be at least 300mm from any opening window. Doors: A minimum distance of 300mm from any door. Velux Windows: Flues should be positioned at least 2,000mm below these windows.
If you have an openable window in your roof and the flue will be within 2300mm either side of it or anywhere below it, then your flue system must rise above the window by 1000mm.
It's generally safe to leave a fan on throughout the night as long as the fan is well-maintained and positioned in a safe and stable location.
For rooms with only one window
When there is only one window, it is effective to open the room door and place a fan or similar device near the window. The most effective method is to turn the fan toward the window and let air outside the room.
You can cool a room with just one window and one fan. Place a box fan in the window or a pedestal fan within 5 feet of the window. When the air is cooler outside than it is inside, point the air so it blows into the house.