Central air ducts are often routed through unconditioned zones in the house, like the attic or crawl space. Serious temperatures in these regions contribute to thermal reduction in metal ductwork. A metallic duct conveying cool, conditioned air through a broiling attic in summer or warm air through a cold crawl area in winter may lose a substantial sum of temperature. These losses can be reduced by insulating metal ductwork with wrap-around insulation.
Purchase duct wrap insulation which complies with the 2009 International Energy Conservation Code (IECC) criteria that define an R-value of 8 for attic ducts and 6 for ducts found anywhere else.
Inspect the period of ductwork to be insulated. Search for signs of air escapes at joints or seams, like streams of dust radiating in a leak. Seal escapes with mastic duct sealant. Verify that duct sections are permanently fastened together at joints. If they aren’t, use sheet metal screws to automatically fasten them, then tape the joints using metal-backed duct sealing tape.
Assess the duct to be insulated. Consult manufacturer’s recommendations for the right size of insulation to adequately enclose the duct perimeter without compressing the insulation and degrading its heat-resisting properties.
Cut insulation to size using a razor blade knife. Trim 2 inches of insulation from the backing on all sides, leaving a flap of financing that will overlap for taping.
Wrap the insulation around the duct using the vapor barrier backing facing out.
Clip the overlapping financing together with duct insulation speed clips in 18-inch periods.
Seal the overlap seam using commercially available pressure sensitive duct insulation tape.
Butt each adjacent section of insulating material up against the previous section, overlapping the backing. Tape the connection between sections to seal them and form a smooth, continuous section of insulation enclosing the whole period of ductwork.