The answer to 'furnace or furnace' is that there is no difference between the two terms. They both refer to the same type of heating system - a central heating appliance that uses natural gas, propane, or electricity to generate warm air and distribute it throughout a home.
Furnaces are the most common type of central heating system found in homes. They work by igniting a fuel source to heat air, which is then pushed through a system of ducts and vents to warm the living spaces. Furnaces are generally more efficient and cost-effective to operate than other heating systems like boilers or space heaters.