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HRV Tandem Hood

Category: Building Codes

Issue/Problem: Spacing of Exterior Vents for Heat Recovery Ventilators (HRV)

Analysis:        
Clarification of the proper spacing of the exterior supply and exhaust hoods or vents for HRV’s.

Since being introduced in the mid 1970’s, HRV and ERV’s have been installed in over a million North American homes. From the beginning there was debate over a suitable location for the supply air intake to ensure a safe, healthy and reliable source of fresh air. Considerations included:

 

Through observation of installed systems it became standard practice by manufacturers to recommend the spacing of hoods be six feet apart as this was known to virtually eliminate problems with frosting. Similarly, manufacturers found that hoods placed 18” above grade avoided fouling from snow, leaves and grass. The early standards for installation of HRV/ERV’s in programs such as the R-2000 program, simply adopted these early common industry practices. However, as more appliances competed for access to the outside through the rim joist of the house, it became clear that restrictions and standards were needed on the placement of hoods generally and specifically the fresh air inlet.

Code:              

“The distance separating outdoor air intakes from building penetrations that are potential sources of contaminants, such as gas vents or oil fill pipes ….. shall be no less than 900 mm.”

Section 8.8.1 of CSA F326 Standard reads:
"Separate air intake and exhaust openings, when located on the same wall or roof, shall be installed so as to prevent contamination of the ventilation air by the exhaust air"

“Concentric or immediately adjacent air intake and exhaust openings shall be constructed and installed so as to prevent cross-contamination"

“… leakage from the exhaust air stream to any supply air stream shall not constitute more than 15% of the exhaust airflow provided by the packaged ventilator.”

 

Conclusion:
While the traditional “best practice” distance between individual intake and exhaust hoods recommended by manufacturers is still six feet, codes and standards have progressed to be more flexible and accommodating.

 

New Home Investment
HRV Installations