insulation duct is one of the most important parts of your home’s air system, a crucial step in keeping your house cool in summer and warm in winter. It also helps your HVAC system run more efficiently, which can help reduce energy costs and increase its lifespan.

Insulated ducts have been standard in new homes for decades and no building inspector worth his salt is going to let builders or homeowners get away with uninsulated ducts. However, a lot of older houses have uninsulated ducts, and many homeowners don’t think about insulating their ductwork. That’s a big mistake. Uninsulated ducts allow unwanted air to leak into your home’s conditioned air, polluting your clean, filtered, cooled or warmed air with unconditioned outdoor air. That means your expensive conditioned air isn’t doing as much work as it should.

If you have old, uninsulated ducts, re-insulating them is a project that will pay for itself quickly in lower utility bills and more efficient operation of your home’s HVAC system. And while it may seem like a daunting task, re-insulating your ducts is actually quite simple with the right materials and basic tools.

The most common and effective insulation for ducts is fiberglass, which comes in different thicknesses (or R-values) and forms (flexible or rigid) and can be used on either the inside or outside of the duct. It’s also moisture-resistant, which is important for a duct that will be running cold air.