Important Notice: Our web hosting provider recently started charging us for additional visits, which was unexpected. In response, we're seeking donations. Depending on the situation, we may explore different monetization options for our Community and Expert Contributors. It's crucial to provide more returns for their expertise and offer more Expert Validated Answers or AI Validated Answers. Learn more about our hosting issue here.
The main difference is the 90% furnace uses a secondary heat exchanger and has a sealed combustion chamber. The secondary heat exchanger traps the moisture that normally escapes out of the flue. As an example: with an 80% efficient furnace you get $80 worth of heat for every $100 you spend on natural gas.
