Drafty Windows & Doors: Small gaps and cracks around windows and doors let cold air seep in, disrupting your home’s temperature balance. Dirty/Clogged Air Filters: When air filters are blocked by dust and debris, airflow is restricted, making it harder for warm air to circulate evenly. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.