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Whole house ventilation

SallyO | Posted in General Questions on

Hello,  I bought a new home last March in the Sacramento area.  In the upstairs bathroom there is a switch with a label that reads: “whole house ventilation system. Leave on unless the air quality is bad.” The questions I have are: Why is the fan installed in the bathroom?  Do I need to leave it on 24/7? What happens if I leave the bathroom door closed most of the time?  My homeowner manual that came with the house does not mention much. I am not sure if the ventilation is mechanical or passive methods. Thanks much, SallyO

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  1. Expert Member
    Dana Dorsett | | #1

    If it's a new home, ask the builder/seller.

    If it's only "new" to you (the new owner of not a new house) or if the builder/seller isn't forthcoming, you'll have to figure out if the switch controls something more than just the bath fan.

    Exhaust-only ventilation is possible to meet the letter (but not necessarily the spirit) of the regulations. It's been awhile since I looked at CA Title 24 specs for ventilation, but I believe the whole house ventilation rate is just a cubic feet per minute number based on ASHRAE 62.2, and the flow of bath fan will count toward that number if operated continuously.

    ASHRAE 62.2 calls out 0.03 cfm per square foot of conditioned space, plus 7.5 cfm per occupant. The term "occupant" is the number of bedrooms + 1. So a 1500' two bedroom house would need:

    1500' x 0.03= 45 cfm plus 7.5 x (2 +1) = 22.5 cfm for a total of 67.5 cfm.

    A 100 cfm bath fan would cover that, but it's not necessarily a great ventilation strategy, since ventilation air coming from random leak points in the house isn't necessarily delivered where it's needed the most, nor is it necessarily coming via a clean uncontaminated path.

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