About Caswell... A UK Leader in Ventilation Ductwork. Over thirty years, Caswell has developed into one of the UK's leading ventilation ductwork Ventilation & Air Conditioning Contractors. Working from our 45,000 sq. ft. premises we pride ourselves on the quality of our products, outstanding levels of customer care and a rapid, effective response to clients' needs. This level of service has helped us to build and maintain strong working partnerships throughout the UK and Eire. Our ongoing programme of investment in state-of-the-art design and manufacturing technology ensures that we continue our competitive edge and industry leadership.