Whole House Fans and Your Home

Author: Pacific Northwest Inspections Group, LLC   Date: 25-Nov-2013.   Category: Energy Effiency, Mold   Add to Favorites 

Washington State Energy Code 2012

Let your whole house fan run 24/7 Your whole house fan was designed to bring in a certain volume of outside air (measured in cubic feet per minute) to meet stringent requirements for air flow and sound control. It is equipped with a control, which can be a standard ON/OFF switch or a programmable timer. It is recommended that you operate the fan 24 hours a day.  

 

Your whole house fan capacity was selected based on the size of the house, the number of bedrooms. The table below shows required continuous ventilation rates (in CFM) for homes of various sizes. 

 

In many cases, a bathroom fan may do double-duty as the local exhaust and the whole house fan. These fans may have a control that sets the continuous operation ventilation rate (in CFM) and a sensor that ramps the fan up to a higher CFM when the room is occupied. This sensor can be set to run the fan for a specific period of time after the occupant leaves the room before it ramps down to the lower CFM rate. 

M1507.3.3 Mechanical ventilation rate. 
The whole-house mechanical ventilation system shall provide outdoor air at a continuous rate of not less than that determined in accordance with Table M1507.3.3(1). 

Exception:
 The whole-house mechanical ventilation system is permitted to operate intermittently where the system has controls that enable operation for not less than 25-percent of each 4-hour segment and the ventilation rate prescribed in Table M1507.3.3(1) is multiplied by the factor determined in accordance with Table M1507.3.3(2). 


TABLE M1507.3.3(1) CONTINUOUS WHOLE-HOUSE MECHANICAL VENTILATION SYSTEM AIRFLOW RATE REQUIREMENTS
 

DWELLING UNIT 
FLOOR AREA 
(square feet)
NUMBER OF BEDROOMS
 1 2 - 3 4 - 5 6 - 7 > 7
Airflow in CFM
< 1,500 30 45 60 75 90
1,501 - 3,000 45 60 75 90 105
3,001 - 4,500 60 75 90 105 120
4,501 - 6,000 75 90 105 120 135
6,001 - 7,500 90 105 120 135 150
> 7,500 105 120 135 150 165

For SI: 1 square foot = 0.0929 m2, 1 cubic foot per minute = 0.0004719 m3/s.


TABLE M1507.3.3(2) INTERMITTENT WHOLE-HOUSE MECHANICAL VENTILATION RATE FACTORSa, b
 

RUN-TIME PERCENTAGE IN EACH 4-HOUR SEGMENT 25% 33% 50% 66% 75% 100%
Factora 4 3 2 1.5 1.3 1.0

a. For ventilation system run time values between those given, the factors are permitted to be determined by interpolation.
b. Extrapolation beyond the table is prohibited.
For State of Washington Homes The requirement is as follows: (2009 Energy Code)

302.3.1 Whole House Ventilation Systems: Each dwelling unit shall be equipped with a whole house ventilation system which shall be capable of providing the volume of outdoor air specified in Table 3-2 under normal operating conditions. 

302.3.2 Whole House Ventilation System Controls: All ventilation system controls shall be readily accessible. Controls for whole house ventilation systems shall be capable of operating the ventilation system without energizing other energy-consuming appliances. 

Intermittently operated whole house ventilation systems shall be constructed to have the capability for continuous operation, and shall have a manual control and an automatic control, such as a clock timer. At the time of final inspection, the automatic control timer shall be set to operate the whole house fan for at least 8 hours a day with a fan rated for CFM noted in table. A label shall be affixed to the control that reads “Whole House Ventilation (see operating instructions).” 

302.3.4 Whole House Ventilation Ducts: All ducts shall terminate outside the building. Exhaust ducts in systems which are designed to operate intermittently shall be equipped with back-draft dampers. All exhaust ducts in unconditioned spaces shall be insulated to a minimum of R-4. All supply ducts in the conditioned space shall be insulated to a minimum of R-4. We recommend meeting this requirement in older homes previous to this code change as well.

A properly ventilated home means good moisture control !!  Moisture = Mold and Decay!

We Test for WA State 2012 Energy Code, Call us @ 425.608.9553 for your Energy Audit and Ventilation Needs -

Note:This service is not standard in a home inspection and is an additional service. Like to add this service to your inspection? Just mention Whole House Fan certification to the inspector, our inspectors are all trained for Residential and Commercial Energy Auditors! Call today 425.608.9553.