Defining Your Thermal Boundary

Simply put, the thermal boundary of a home is the line that separates your warm-conditioned spaces from the cold unconditioned spaces (either outside or unfinished spaces like attics and crawl spaces). This boundary usually includes the basement perimeter sill, exterior walls, doors, windows, and the attic floor. This can vary depending on how your home is set up, but thinking about what surfaces separate your living space from non-living/non-conditioned space is the best way to put it. It is essential to not only insulate and air seal your thermal boundaries but also to define them properly based on the setup and goals of your home. The Mass Save Program has huge discounts towards better defining these boundaries and getting them insulated and air sealed up to and beyond town code! Green Energy Gains plays a direct role in this by doing the no-cost home energy assessment and providing these insulation improvements at the Mass Save Program discounts. While each house is different and should be assessed individually, typically you find that defining your thermal boundary to make your home “as small as possible” will yield the best results. The volume of your home added up in total is directly correlated to the amount of energy you will use to keep comfortable both in summer and winter. You typically do not need to pay to heat your attic space, unfinished knee wall eave spaces, or crawl spaces. These are areas of the home that are unused and trying to keep them as conditioned space is an uphill battle. 

By defining the thermal boundary as the attic floor, the rest of the attic cap is left unconditioned and should be vented to code. This means your attic stays as close to the true outdoor temperature as possible. By insulating and air sealing the attic floor, you are less likely to have a warm attic causing ice dams in the winter. During the summer, insulating the attic floor and leaving the attic cap unconditioned means you’ll spend less money on AC (less volume of the home when the attic cap isn’t included in your thermal boundary), and avoid excessive heat buildup that can damage the roof sheathing and shingles (thanks to proper ventilation).

Having a well-defined thermal boundary is one of the main goals of the Mass Save program. If you think your home is losing heat through gaps in the thermal boundary, or you believe your thermal boundary is set up incorrectly, A Mass Save assessment is an easy and no-cost step to take towards assessing the cost/benefit of making corrections. Give us a call so we can help inspect the continuity of your home’s existing insulation and air barriers!