This report investigates the possibility that energy losses due to air leakage from ducts in small buildings might be reduced if the leaked air is constrained to flow within the insulation to a point upstream or downstream of the initial leakage point. The idea is that the leakage air might warm (or, in the air-conditioning mode, cool) the insulation and thereby retard heat conduction from (or to) the duct. Any such reduction in conductive losses could be credited against the lost energy from the leak itself Theoretical calculations carried out in this work indicate that such a 'thermal regain' effect could recover, in the heating mode, up to half the heat contained in the leaking air, and En the cooling mode, up to 75% of the sensible cooling in the leak. In most actual cases, a smaller amount of regain would be expected.