Astria Outside Air Kit With Duct OAK-UVFRCAstria OAK UVFRC Outside Air Kit with Duct for Vent Free Fireplaces How does the Astria OAK UVFRC Outside Air Kit improve fireplace efficiency and indoor air quality? The Astria Outside Air Kit with Duct offers key features and benefits that make it a valuable addition to your fireplace system for improving air quality and efficiency. It provides a dedicated source of fresh air from outside, which enhances combustion efficiency and reduces the demand