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Technical Corner

Ventilation Systems

The 10 rules for proper HRV design & installation

Because R-2000 believes that the ventilation system is one of the most important elements in a home, R-2000 houses not only have HRV systems installed but program requirements insist that they be designed and installed properly. Our final inspection checks to insure that the following items are corrected in place.


  1. Ensure that the installing contractor is currently certified by the Heating Refrigeration & Air Conditioning Institute of Canada (HRAI) and that all R-2000 ventilation report forms are filled out.
    Why? — Ensures that the person installing the system has at least a minimum level of knowledge and thinks about the design and final system operation.

  2. Size the HRV capacity for the amount of potential occupied space in the house:

    • 20 cfm for master bedroom and unfinished basement
    • 10 cfm each for all other habitable rooms
    Why? — Ensures that the HRV is sized to accommodate the maximum amount of pollutants the house can potentially generate if all habitable rooms were occupied.

  3. Install controls capable of reducing the continuous low speed ventilation rate to 40% – 60% of maximum.
    Why? — The maximum rate as calculated in rule #2 assumes that all rooms will be occupied, which is seldom the case. Operation at maximum likely provides too much ventilation if the home is not fully occupied. The lower ventilation level is likely appropriate for 80% of the time the house is normally occupied. Consideration should be given to installing the best controls available to provide homeowners with the maximum degree of ventilation control to allow them to adjust the system to meet the ventilation requirements of individual family’s lifestyles. At the very least, a four wire control wire should be roughed in to allow for the HRV control to be upgraded at some future date.

  4. Install permanent air flow measuring stations and balancing dampers on air supply and exhaust ducts and balance the flow rates to be within 10% of each other.
    Why? — To keep house pressures in balance and prevent excessive HRV freeze ups.

  5. Ensure that the insulated flexible duct used to bring the cold outside air into the HRV is limited to 10' in length or less, that its terminations are well sealed at both the HRV and inlet hood, and that soft "non-metallic" material at least 2" wide is used for intermediate duct support.
    Why? — Duct length in excess of 10' reduces the heat recovery efficiency of the HRV. Improperly sealed terminations will allow for condensation and ice build up on duct. Standard metal duct hanger supports tend to compress the duct insulation and cut into the polyethylene vapour barrier covering.

  6. Supply the HRV fresh air to the furnace return air plenum at least six feet away from the furnace.
    Why? — Dependant on exterior air temperatures, even after the heat exchange process, the HRV supply air can still be fairly cold. Proper mixing of the cold fresh air with the warmer household return air needs to be accomplished to prevent excessive cooling of a fuel fired furnace's heat exchanger.

  7. Locate the kitchen exhaust grill at least four horizontal feet away from the stove and install a grease filter behind the grill.
    Why? — The HRV inlet in the kitchen is only designed to provide low level background exhaust. The main exhaust of cooking pollutants is done by a range hood located directly above the stove. The grease filter prevents excessive grease build up within ductwork.

  8. On the exterior of the house, separate the HRV supply and exhaust air hoods by at least 6 feet and insure at least 18" clearance to ground on the intake and 4" on the exhaust hoods.
    Why? — To prevent cross contamination of supply and exhaust air flows and blockage of vents by snow.

  9. Interconnect the HRV with the forced air furnace fan so that when the HRV is operating the furnace fan is also operating.
    Why? — To facilitate proper mixing and distribution of fresh air into all areas of the house.

  10. Install air flow balancing dampers on all exhaust duct branch runs.
    Why? — To enable the exhaust flow rates from each room to be adjusted.

 
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