Walls are another part of your home’s structure where heat can be lost in winter and gained in summer. If ductwork carries conditioned air through your home, it should be air-sealed and insulated to keep the air inside the ducts at its desired temperature.

To get your walls and ductwork evaluated (in addition to the rest of the home), schedule a no-cost Home Energy Assessment with Mass Save. Their home energy professionals will provide you with energy-saving products to install yourself, recommend additional upgrades, and coordinate air sealing and insulation services with weatherization contractors if needed.

Blower door tests are not included with a typical home energy assessment, but it may be worth the $300 – $600 cost to identify additional opportunities for weatherization.


Adding insulation slows heat transfer through the building envelope (walls, roof, floors, etc.); heat transfer is the leading cause of heat loss in the winter. Working with a professional contractor to improve wall insulation can considerably lower heat transfer, improving your home’s efficiency. Many insulation contractors are trained to air-seal before insulating, when it’s much easier to do.

A few changes that may be made:
  • If your home has walls or parts of walls that are poorly insulated, you can add more insulation. Dense-pack cellulose is a common, environmentally sustainable type of insulation that can be blown into your home’s walls.
  • If your home has knee walls, insulating them can prevent air from leaking out of your living space into the roof area. A home energy professional can add insulation between the studs of a knee wall and put rigid foam board insulation on the exterior-facing side of the knee wall.


If your home utilizes a centralized heating or cooling unit with ducts outside of the conditioned space of the home (e.g., in an attic, basement, garage, or crawlspace), sealing and insulating the ducts can significantly improve the overall efficiency of your system by ensuring that more of the heated or cooled air gets delivered to where it is needed. ENERGY STAR® estimates that in typical houses, 20% of the air that moves through the duct system is lost due to leaks, holes and poorly connected ducts. Your Mass Save weatherization contractor may be able to better seal and tape leaky ductwork to decrease wasteful air leakage.

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