Which gas appliance is considered to be 100% efficient?

The direct fired make-up air unit is considered to be 100% efficient because it uses the combustion process to directly heat incoming air before it is circulated throughout a space. Since it provides heat directly, there is no loss of energy in the form of heat escaping through ventilation or flue systems, which can often occur in other gas appliances. This type of system effectively utilizes all of the energy from the fuel consumed, making it highly efficient for heating the air being introduced into a space.

In contrast, standard furnaces, vented gas heaters, and traditional gas stoves can experience heat loss due to the nature of their design, which often includes exhaust systems that release unutilized heat into the atmosphere. Therefore, while these appliances may be quite efficient, none achieve the same 100% efficiency as a direct fired make-up air system.