Boilers

A heating boiler comprising in combination:

• a combustion chamber;
• a hopper having a throat opening into one side of the combustion chamber at a level such that solid fuel pellets in said hopper flow out to form a firebed until the surface of the firebed slopes downwardly from said throat at the natural angle of repose of said fuel pellets;
• a thermostatically controlled fan operable to cause primary air to flow through the firebed;
• a support that slopes downwardly into the combustion chamber for an initial portion of the downward travel of the fuel pellets;
• a regulator extending generally across said throat for controlling flow of fuel pellets from said hopper;
• and
• means on said regulator for defining a localized thinning of the firebed so that the firebed is shallow at the localized region with respect to the thickness of the firebed adjacent said localized region, said means including a tongue mounted on said regulator, said tongue having a longitudinal area less than the cross-sectional area of said throat so that the tongue at least substantially prevents the flow of fuel pellets at one region of said throat downstream of said tongue so that a localized shallow region forms in the firebed through which breakthrough of primary air is facilitated and controlled while maintaining a thick edged firebed, said regulator being spaced from said support so that the effective throat, between the regulator and the support, is less than about 40 mm so that fuel pellets having sizes equal to or less than about 5/16 inch can be efficiently handled by the boiler.