Anyone who has ever sat near a cold window on a winter day or in direct sunlight on a hot day recognizes that windows can cause thermal discomfort. In spite of this broad recognition there is no straightforward method to quantify the extent of such discomfort. HVAC designers specify dedicated perimeter heating and cooling systems to mitigate window-related comfort problems, yet they use simplified assumptions that may not solve the comfort problems or that might lead to designs that are energy-inefficient.