Small-duct HVAC system manufacturer Unico Inc. is marking the 15th anniversary of working with the National Trust for Historic Preservation by giving away a free trip to Florida to see its systems in two notable structures.

Through Wednesday, the public is invited to enter a sweepstakes to win a trip to Key West, Florida — the site of two historic structures that feature Unico systems: the former home of Ernest Hemingway and the “Little White House,” the vacation home of former President Harry S. Truman.

“Unico is very proud to renew our long-standing partnership with the National Trust,” said Unico marketing director Scott Intagliata. “It’s a natural fit since our product, The Unico System, provides efficient central heating and cooling to older or historic homes and buildings without altering the original architectural integrity of these structures.”

Andrew Simpson, vice president of marketing for the National Trust for Historic Preservation, pointed out that many structures managed by the trust feature Unico’s HVAC equipment.

“Unico’s expertise brings modern comfort to historic homes and properties with sensitive restorations,” Simpson said. “We thank Unico for its generous and continued support as a partner of the National Trust.”