The Honeywell ER90 Air Exchanger is a ducted fresh air device which brings fresh air into your home or office while at the same time exhausting stale air. While the air is passing through the Honeywell Air Exchanger, energy from the stale air is transfered to the fresh air in order to reduce the energy required to warm or cool it to room temperature. This allows you to bring in fresh air without having to pay the cost of heating or cooling it. Normal maintenance on the Honeywell Energy Recovery Ventilator consist of checking and cleaning at least twice a year the its filters and energy core, preferably at the beginning of each heating and cooling season.