Patent ID: 7222591

Claim:
Fuel-fired heating apparatus comprising: a combustion chamber; a fuel burner disposed within said combustion chamber and operative to create hot combustion products therein, said fuel burner being progressively cloggable by particulate matter entrained in primary combustion air delivered thereto during firing thereof; a first air supply structure for supplying primary combustion air to said fuel burner from outside of said combustion chamber without exposing the supplied primary combustion air to the interior of said combustion chamber on its way to said fuel burner; a second air supply structure for receiving secondary combustion air from outside said combustion chamber and discharging the received secondary combustion air into the interior of said combustion chamber, at a discharge velocity, for flow therethrough to said fuel burner, said second air supply structure being progressively cloggable, at a greater rate than said fuel burner, by particulate matter entrained in the received secondary combustion air in a manner progressively reducing said discharge velocity; and a system for monitoring said discharge velocity and responsively terminating operation of said fuel burner when said discharge velocity decreases to a predetermined magnitude.