Retrofitting an HRV

A heat-recovery ventilator (HRV) pulls in fresh outdoor air while exhausting stale air from indoors.

The HRV pulls fresh air into the house while exhausting stale air to the exterior. The two streams pass, without mixing, through a heatexchanger core, where heat from the outgoing air is transferred to the incoming air.

In fully ducted systems, habitable rooms are served by supply ducts, while rooms where pollution and humidity are generated get exhaust ducts.

Where a cold-side run of rigid duct is unavoidable, as in a garage, the pre-assembled duct can be slipped inside the foil-faced insulating jacket from a length of flex duct.

A duct carrying stale air from the HRV passes through the rim joist and connects to a riser hood (left) that directs the exhaust to an exit point 18 inches above grade (right).

In this installation the exhaust and intake are high in the wall and separated 6 feet horizontally to meet code. The intake louvers are permanently open, but the exhaust louvers open only when the HRV is running.

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