First let’s start off with a little lyric from the classic rock band Pink Floyd-

“Breathe, breathe in the air.  Don't be afraid to care. “

I have said this many times before, I seem to run into certain conditions or items during a home inspection in groups. Recently it has been missing outdoor fresh air supply for whole house ventilation systems.

Our modern day building practices have created much tighter building envelopes. As we do this we are now restricting the amount of fresh air that bypasses the envelope. This is great for energy performance but bad for air quality. These are not your Grandma’s old leaky house anymore.

Because of this tighter building envelope we need to introduce fresh air into the home to provide good indoor air quality. This can be accomplished by several means. It could be from fresh inlets in walls and windows, HRV’s or what I am used to seeing is fresh air being brought in via the return duct on the forced air system.

Washington State requires a method to introduce fresh air, and there are several options.  Below is the code.

(Link to WAC)   http://apps.leg.wa.gov/wac/default.aspx?cite=51-51-1507

(State Building Code adoption and amendment of the 2012 edition of the International Residential Code)

WAC 51-51-1507            Section M1507—Mechanical ventilation.

M1507.3.4.4 Outdoor air inlets. Outdoor air shall be distributed to each habitable space by individual outdoor air inlets. Where outdoor air supplies are separated from exhaust points by doors, provisions shall be made to ensure air flow by installation of distribution ducts, undercutting doors, installation of grilles, transoms, or similar means. Doors shall be undercut to a minimum of 1/2 inch above the surface of the finish floor covering.

(The option below is what I normally see)

M1507.3.5.1 Integrated whole-house ventilation systems. Integrated whole-house ventilation systems shall provide outdoor air at the rate calculated using Section M1507.3.3. Integrated forced-air ventilation systems shall distribute outdoor air to each habitable space through the forced-air system ducts. Integrated forced-air ventilation systems shall have an outdoor air inlet duct connecting a terminal element on the outside of the building to the return air plenum of the forced-air system, at a point within 4 feet upstream of the air handler. The outdoor air inlet duct connection to the return air stream shall be located upstream of the forced-air system blower and shall not be connected directly into a furnace cabinet to prevent thermal shock to the heat exchanger. The system will be equipped with a motorized damper connected to the automatic ventilation control as specified in Section M1507.3.2. The required flow rate shall be verified by field testing with a flow hood or a flow measuring station.

M1507.3.6 Whole-house ventilation using a supply fan.

M1507.3.6.1 Outdoor air.

Supply fan ventilation systems shall distribute outdoor air to each habitable space through the forced-air system ducts or through dedicated ducts to each habitable space. Supply fans shall have the capacity to provide the amount of outdoor air specified in Table M1507.3.3(1) at 0.40 inches water gauge as per HVI 916. The outdoor air must be filtered before it is delivered to habitable spaces. The filter may be located at the intake device, in line with the fan, or, in the case of a connection to the return plenum of the air handler, using the furnace filter. An outdoor air inlet shall be connected to either the supply or return air stream.

There are also HRV (Heat Recovery Ventilators) and ERV (Energy Recovery Ventilators) options but are not very common, but I think they will and should be the future.

Washington state has required Whole House Ventilation in homes since  July of 1991. So this is not a new thing. Fresh air is really needed to ensure a healthy indoor environment.

But in the world of code there are often exceptions and unfortunately Washington State put one in and some municipalities have and will take advantage of, if they know about it.

This exception is WAC 403.8.11 Alternate systems- When approved by the code official, systems designed in accordance with ASHRAE Standard 62.2 shall be permitted.(bold underline is mine)

This is where in ASHRAE the view is that natural air infiltration (leakage) can make up for fresh air, but this is a poor idea if we are trying to control how air infiltrates the envelope.

Studies by Washington State have shown when natural air infiltration is being used that the majority of the air is coming from the crawlspace and garage, in that order. Not exactly the places we want our fresh air to come from.

The issue with providing fresh air, other than the HRV/ERV systems, is that they are not perfect, and proper distribution is often not achieved.

Here is the code reference for the exception-

WAC  WAC 51-52-0403 Section 403—Mechanical ventilation.

Link-  http://apps.leg.wa.gov/wac/default.aspx?cite=51-52-0403

(State Building Code adoption and amendment of the 2012 edition of the International Mechanical Code.)

Joe Lstiburek of Building Science Corp came to the rescue. Because of the ASHRAE 62.2 Joe created his standard

Link-  Ventilation for New Low-Rise Residential Buildings

For further reading on the subject if mechanical ventilation-

Impact of Residential Mechanical Ventilation on Energy Cost and Humidity Control

“If you think it's expensive to hire a professional to do the job, wait until you hire an amateur.”

Red Adair

NCW Home Inspections, LLC  is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…  

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