What is a heat recovery ventilator? In simplest terms, an HRV circulates fresh air in a home and exhausts used stale air to the outdoors, while recovering the heat contained in the exhaust air. A typical HRV, a Zehnder Q350 for example, has 4 ports for handling air. Fresh outside air will come in through one port, pass through a dust filter, and then pass through a heat exchanger where it recovers the heat from air leaving the house. The fresh air continues out the other side through the distribution port where it is then ducted to the living spaces such as bedrooms and common areas. As occupants live and breathe in their houses, oxygen from the fresh supply air is used up and CO2 and water vapor are produced. Cooking creates more vapor and other chemical compounds, bathrooms contain yet more vapor, odors and chemicals from cleaning and use. Exhaust registers are placed in these areas to pull the air and all the unwanted items from the rooms, promoting circulation of the fresh supply air. This exhaust air is pulled through another dust filter on the opposing side to the intake filter, it then passes through the same heat exchanger, but through a different channel, passing on the heat energy of the inside conditioned air without ever touching and contaminating the fresh air supply, this is then exhausted through the last port on the unit to the outside.