There purposes of ventilating a home are to exhaust excess moisture and contaminants and to provide fresh air to dilute indoor pollutants. Furthermore, it is required by code, is necessary and works!

All new homes now require a ventilation system as per the National Building Code (NBC). It needs to be properly sized and installed correctly. In Canada the most common type of system installed is a Heat Recover Ventilator (HRV).

Building Code Requirements

The National Building Code (NBC) provides instructions on ventilation systems that must meet the following criteria:

• Mechanical ventilation equipment must be provided
• Ventilation Systems must be capable of operating on a continuous basis
• The ability to exhaust from each bathroom and the kitchen must be provided
• Ventilation system controls must be provided to allow for both continuous operating levels and higher peak exhaust rates
• Where the operation of exhaust equipment can induce significant negative pressures, the ability to provide fresh air to the house must be in place
• Allow fresh air to be distributed to all habitable rooms
• Supply fresh air from an uncontaminated source
• Not cause back drafting of combustion appliances
• Should be easy to maintain and affordable to install and operate
• CO monitors are required in homes with fuel-fired appliances (Like a woodstove)

Ventilation Systems

A ventilation system may be a stand-alone system (separately ducted) or may be tied into a furnace (combined system) making use of ducting that is already in place. A stand-alone system will usually have 2 ducts that penetrate the exterior of the building - the supply and exhaust (There are some new systems that incorporate coaxial ducts). A ducted system may be more robust throughout the home but will also have 2 exterior penetrations for the supply and exhaust. Although rare, a larger home may have more than one ventilation system, which can lead to additional exhaust and supply penetrations to the exterior

Common Ventilation Systems

HRV's are the most common type of ventilation system used in Canada and NBC requires new home ventilation systems to have 50% heat recovery while the OBC requires 55%. Additionally, air exchanger systems are sometimes installed in existing homes depending on the degree of the renovation and airtightness.

While ERV's are another option but suited better for warmer southern climates.

An HRV system generally consists of the following equipment:

• Insulated ducts for incoming (fresh) and outgoing (stale) air, along with exterior hoods
• Ductwork to distribute fresh air throughout the home and to return stale air to the HRV (Some are combined with existing forced hot air ducting)
• Fans to circulate air throughout the home and to exhaust stale air to the outdoors
• A heat-exchange core, where heat is transferred from one air stream to the other without mixing the two volumes
• Filters to keep dirt out of the heat-exchange core
• A defrost mechanism (some units use a preheater) to prevent freezing and blocking of the heat-exchange core when the temperature of the incoming air is cold (not shown)
• A drain to remove any condensation from inside the HRV (may not be required with all models)
• Operating controls to regulate the HRV according to ventilation needs

Existing Home Renovations

As houses get more airtight the need to ventilate increases. This is to maintain:

• The occupants comfort
• Good IAQ (indoor air quality)
• Proper moisture levels

The tighter the home the more important it is to control moisture and maintain IAQ with ventilation. Otherwise, moisture can build up in the home and destroy components such as wood, making the home structurally unsafe, while also causing health issues for the occupants.

Many existing homes may not have a ventilation system and when upgrading a home it can become more airtight. A tighter home keeps more moisture in and an upgrade can lead to moisture, condensation and IAQ problems if steps are not taken to control these elements.

Keep this in mind and consider whether an upgrade may improve the tightness of the home and if so recommend the installation of a ventilation system to the home owner

Ventilation System Installation

If you are insulating during/after a ventilation system is installed make sure to:

• Seal all ductwork penetrations in the exterior walls
• Seal all ductwork coming from the top floor ceiling or attic if the system is installed there

Close attention must be given to all penetrations from the exterior walls/attic as they greatly effect airtightness. Continuity of the air barrier must also be maintained in order for the house to perform as expected.

Outside Hoods (Supply and Exhaust)

The F326 standard requires that the supply and exhaust be far enough apart to prevent cross-contamination. (Industry suggested separation is 6 feet apart (inside to inside)) Although building codes have several paths to compliance the CAN/CSA-F326-M91 (R2010) "Residential Mechanical Ventilation Systems" is the most popular path taken. This is also true for energy efficiency programs such as R-2000 and NetZero. Note that some engineered two-in-one hoods do not need the clearance.

The reason for this is to prevent exhaust air from re-entering the home through the supply intake, which can lead to poor Indoor Air Quality (IAQ). Remember this requirement when sealing around the supply and exhaust ductwork. If it is not going to meet this requirement, mention this to the ventilation installer or builder before the installation is completed. It is much easier to fix the ductwork before the install is complete, and you do not want to be called back to re-seal the ductwork to your air barrier after you are finished your job. Call-backs increase project costs.