How do I choose the correct furnace or air handler's cabinet width?

Cabinet width refers to the physical size of a furnace or air handler's housing — typically 14.5", 17.5", 21", or 24.5" wide. Choosing the right width ensures the furnace fits your existing ductwork and coil cabinet. If you’re replacing an existing system, match the width of your old equipment for easiest installation. For new installations, consult your contractor or check your coil and plenum dimensions to determine the proper size.