How do I size my Fantech bathroom exhaust system?
IF your bathroom is 100 sq.ft. or smaller
According to the guidelines of HVI (Home Ventilating Institute) baths that are 100 sq.ft. or smaller require1 CFM per square foot of bathroom or a minimum 50CFM of fresh airflow. To find the square footagesimply multiply the length of the bath by the width. For proper airflow in typical installations (when duct losses aren’t calculated), use the 0.4” Ps (static pressure) rating point for correct fan selection.
IF your bathroom is over 100 sq.ft.
Ventilation for baths over 100 sq.ft. is calculated based on the fixtures in the bath. Allow 50CFM for each standard toilet, shower or tub. Whirlpool and jetted tubs are calculated at 100 CFM. Add up the CFMs for all fixtures and you will have calculated the total CFMs required.
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How many bathrooms can I vent with one fan?
Fantech generally recommends that no more than 3 bathrooms are exhausted together. Whenever the fan runs air will be exhausted from all the rooms that are connected to one system. This, in combination with the much higher cost of large fans, means that it is generally beneficial to exhaust a maximum of 3 smaller, or 2 larger, bathrooms together.