| The following are guidelines for ventilating both large and smaller
bathrooms using intermittent or continuous ventilation.
Small rooms: 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. Example: Bathroom is 8'x5' (with 8' ceilings). Multiply 8 x 5 =
40ft. Bathroom area is 40ft. At 1 cfm per square foot the minimum
recommendation is a fan rated at 40 cfm.
Larger rooms: For bathrooms above 100 square feet in area, HVI
recommends a ventilation rate based on the number and type of fixtures
present, according to the following table: Toilet 50 CFM Shower 50 CFM
Bath Tub 50 CFM Jetted Tub 100 CFM Note: Enclosed toilet rooms must have
an operable window or a fan for ventilation. Example: The bathroom is
20'x12'. There is a tub (without jets), a shower enclosure and an enclosed
toilet. Each fixture requires 50 cfm: Tub 50 cfm Shower 50 cfm Toilet 50
cfm Total 150 cfm.
You have two options:
1. Install a 50cfm fan over the tub, one in the shower and in the water
closet. This method is very effective and will provide ventilation where
you need it, when it's needed.
2. Another option is to install one 150 cfm fan. The air will then be
pulled through the entire room and exhausted at a central location.
Location of exhaust points: Typically the exhaust points shall be
located over or near the shower or tub and in an enclosed water closet.
With windows closed, exhausted air will be replaced by makeup air from
adjacent rooms or forced air system registers. HVI recommends that the
exhaust points are located away from the supply, thereby pulling the
supply air through the room. Bathroom doors need to be undercut to allow
makeup air to enter the room.
Duration of ventilation: HVI recommends that the fan be left on for 20
minutes after use of the bathroom. A timer is a good solution, allowing
the fan to turn off automatically at the proper time. For steam showers it
is best to have a separate fan in the steam room that can be turned on
after use. Continuous ventilation: Alternatively, ventilation may also be
provided on a continuous basis at other rates. This may complement the use
of fans to provide the HVI recommended rates.
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