Advice for reducing sound from HRV return ducts

A homeowner rebuilding a small, tightly sealed 1948 cottage in Eugene, Oregon ran into a noise problem with their heat recovery ventilator, or HRV — a device that constantly exchanges stale indoor air for fresh outdoor air while recovering heat from the outgoing air. The unit, a Broan model set to run around the clock at its lowest speed, was sending noticeable sound back through the return ducts and out through two vents. Testing pointed to the fan and motor noise inside the unit itself as the source, rather than air turbulence or rattling ductwork.

The homeowner's fix involves rerouting the metal ducting with acoustic silencers (in-line mufflers that absorb sound as air passes through), gentler duct bends, and a section of flexible duct to break up the noise path before it reaches the room vents. One experienced commenter agreed that these in-line silencers work well and suggested starting with just one installed in the main duct before it splits toward the two vents, then checking whether that alone solves the problem. If sound persists, swapping the last stretch of rigid duct near each vent for flexible duct was offered as a simple next step, since flexible duct absorbs sound better than rigid metal as long as it stays fairly straight.

For anyone installing or living with a similar ventilation system, this is a reminder that duct layout, bends, and materials can matter as much as the equipment itself when it comes to keeping a heat-recovery system quiet.