I hear a constant humming from my HRV system, how do I dampen that noise?

HRV humming is typically caused by vibration transmission through rigid connections and can be significantly reduced through proper isolation and ductwork modifications. The most effective solutions involve decoupling the unit from the structure and addressing sound transmission through the ventilation ducts.

Understanding HRV Noise Sources

The constant humming you're hearing likely comes from three main sources: the HRV unit's motor and fan vibrations transmitting through rigid mounting brackets into the floor joists and walls, airborne noise from the unit itself radiating into surrounding spaces, and sound traveling through the ductwork to registers throughout your home. In Ottawa's tightly built homes, especially newer construction in areas like Barrhaven and Kanata, HRV systems are essential for air quality but can become noise sources when not properly isolated.

Motor vibration isolation is the most critical fix. Replace rigid mounting brackets with vibration isolation pads or spring isolators rated for your HRV's weight. Neoprene pads ($15-$30 each) work well for lighter units, while spring isolators ($40-$80 each) are better for heavier commercial-grade HRVs. Ensure all connections to the unit use flexible materials — rigid metal ductwork connections should have flexible canvas or rubber boot connectors within 3-4 feet of the unit to prevent vibration transmission.

Ductwork modifications can dramatically reduce noise transmission. Wrap supply and return ducts near the HRV with mass loaded vinyl (MLV) at $1.50-$3.00 per square foot, then cover with acoustic duct wrap or standard duct insulation. Install acoustic duct silencers ($80-$200 each depending on size) in the main supply and return ducts — these contain sound-absorbing baffles that reduce noise without significantly restricting airflow. For severe noise issues, consider installing the HRV in an acoustic enclosure built with double-wall construction and acoustic mineral wool insulation.

Addressing Ottawa-specific factors is important for long-term success. Our extreme temperature swings mean HRV systems work harder in winter, potentially increasing noise levels. Ensure your unit is properly balanced — an unbalanced system works harder and creates more noise. The Ontario Building Code requires HRV systems in homes built after 2012, but doesn't specify noise limits, so addressing this proactively improves comfort significantly. Schedule maintenance during shoulder seasons (spring/fall) when the system isn't working as hard.

Common mistakes to avoid include using rigid foam insulation around the unit (which can actually amplify certain frequencies), connecting ductwork directly to the unit without flexible connectors, mounting the HRV directly to drywall ceilings without proper structural support, and ignoring the return air path — both supply and return ducts transmit noise equally. Also, don't assume the problem is just the HRV itself; sometimes noise comes from poorly designed ductwork with sharp bends or undersized ducts that create turbulence.

Practical installation tips include checking that your HRV is level (unlevel units vibrate more), ensuring adequate clearance around the unit for service access, using acoustic caulk around any wall or ceiling penetrations, and considering the unit's location — basement mechanical rooms are ideal, but avoid mounting directly below bedrooms if possible. In Ottawa's climate, ensure any acoustic modifications don't interfere with condensate drainage, which is critical during our humid summers.

For a comprehensive solution that addresses both the mechanical isolation and ductwork modifications, it's worth consulting with an HVAC contractor experienced in noise control who can assess your specific installation and recommend the most effective combination of treatments for your situation.