Several companies now make pellet-fired furnaces and boilers for replacement of, or a supplement to, gas or oil fired furnaces and boilers in residential space heating systems. All pellet fuel appliances have a fuel hopper to store the pellets until they are needed for burning. A feeder device, like a large screw, drops a few pellets at a time into the combustion chamber for burning. How quickly pellets are fed to the burner determines the heat output. The exhaust gases are vented by way of a small flue pipe that can be directed out a side wall or upwards through the roof.
More advanced models have a small computer and thermostat to govern the pellet feed rate.
In top-fed systems, the auger is inclined at an angle and feeds the pellets into the top or side of the combustion chamber. Top-fed systems, however, may not force ash away from the firebox grate. Clinkers may impede combustion air flow and cause the fire to die. Bottom-fed designs generally have a horizontal auger. Since this system moves the fuel horizontally into the fire chamber, incoming pellets shove aside ashes and clinkers, which then fall into the ash pan.