Residential furnaces typically have outputs that range from 40,000-150,000 BtU/hr. Efficiency rates range for combustion furnaces range from 89-96%. Electric resistance units are 100% efficient.
Combustion air is introduced through a manually or mechanically controlled inlet. Ideally, this combustion air is supplied through a sealed inlet directly from outdoors. This is nearly always the case with pellet burning units, but not as common with wood stoves.
Exhaust is vented through a chimney. This is accomplished passively in some units (mostly wood stoves), relying on the warm temperature of spent exhaust gas to provide an upward draft.
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A fan may be incorporated to actively move heat from the stove into the room. Minimal ductwork is incorporated in some units. Rare models feature the ability to heat water within the stove. This can be a contribution to hydronic space heating and/or domestic hot water.
Fuel for wood stoves is manually input directly into the firebox through an opening door. Pellet stoves use an auger to automatically deliver fuel for combustion from a supply hopper. This hopper must be filled with pellets as required. Large hoppers can be used to ensure long periods of unattended operation.