Yes, a window can let some nice winter solar warmth in, but the window is also a very poor insulator compared to a wall, so does the solar gain compensate for the heat loss?

There’s nothing quite like a 48% slice of pie in the face to drill home the importance of air leakage.

The thing that piqued my interest in Allison’s article was how his rule of thumb, 37W/m2 compares to our rule of thumb for design of 120W/m2. It is about 70% less! …………….. This highlights the difference between a guess based on the fear of not wanting to under-size a system, and a calculated design based on parameters specific to the building.