Final answer:
When appliances are installed in a separate enclosed space with access only from the outside, combustion air is not required, as the appliances can draw in air from the outside environment through vents or openings in the enclosed space.
Step-by-step explanation:
When appliances are installed in a separate enclosed space and access is only provided from the outside, combustion air is not required. This is because the appliances can draw in air for combustion from the outside environment through vents or openings in the enclosed space. The combustion air intake from outside ensures that the appliances receive sufficient air for proper combustion and operation.
Having an external air supply for combustion not only prevents heat loss, but it also helps to increase the energy efficiency of the appliance. When room air is circulated around the outside of the firebox and back into the room, convection is the method of heat transfer involved.
Two methods to increase the energy efficiency of a fireplace involve heat transfer. The first is the external air supply for combustion, which employs convection - the process of heat transfer through fluids (air or liquid) that move from hot to colder areas. The second is circulating room air around the outside of the firebox and back into the room, which also uses convection to transfer heat from the firebox to the circulating air, which then heats the room more evenly and efficiently.