Furnace specifications are available online at manufacturer websites including Lennox, Carrier, Rheem and Trane and at FindTheBest.com, as of 2015. The manufacturer websites list their own products' specifications, while FindTheBest.com aggregates furnace specifications from numerous makers.
Common listed specifications include efficiency rating, motor type, heat exchanger type and whether it's Energy Star rated. Other important specifications listed are energy capacity and installation type.
Trane lists each furnace's physical dimensions along with warranty details.
FindTheBest.com's lists are sortable by home size, and the lists include prices from Amazon.com, estimated annual savings, energy efficiency and Smart Rating, which is a tool the website uses to weigh different attributes and assign the products' numbers.