Melrose Industries PLC (LSE:MRO) is preparing to sell the bulk of its Nortek Inc. division, in what could become the British buyout specialist’s biggest divestment in more than four years, people with knowledge of the matter said. Melrose is working with advisers to weigh options for the division’s air businesses, which sell products including ventilation and cooling systems, according to the people. It is seeking to raise more than $3 billion from the sale, the people said, asking not to be identified because the information is private. The operations Melrose is planning to divest include the Global HVAC business, which makes large heating and air-conditioning systems installed during residential construction, as well as Air Quality & Home Solutions, which sells products like range hoods and bathroom ventilation fans, the people said. Both are housed in Melrose’s Nortek Air & Security division. A deal could rank as Melrose’s second-biggest disposal of all time, according to data compiled by Bloomberg. It would trail only the £3.3 billion-sale of Elster, a maker of gas and water meters, to Honeywell International Inc. in 2015, the data show. No final decisions have been made, and Melrose could decide to keep the assets for longer, the people said. A representative for Melrose declined to comment.