Modular solid fuel furnace system

Abstract

A solid fuel burning system which may be readily combined with a conventional fluid fuel burning furnace in a forced air heating system. The solid fuel burning system comprises, in combination, a draft inducing blower which directs air for combustion into the furnace at a point proximate the burning fuel. Baffle walls are provided which separate the smoke and other products of combustion from the clean air to be heated and a novel heat exchanger comprised of a plurality of elongated tubes provide a relatively large heat transfer surface. The furnace is specifically designed to facilitate periodic cleaning of the interior walls of the heat exchanger where creosote and other products of combustion may accumulate. In addition, the system employs a novel electronic control circuit which is tied in with the room thermostat and with a thermocouple disposed within the solid fuel burning furnace. The output of the thermocouple is amplified and applied to a series of comparators whose outputs are used to perform various control functions. Specifically, the output from a first comparator indicates that a fire is present in the wood burning unit. A timer mechanism comprised of electronic circuitry becomes operational upon closure of the room thermostat contacts and if the temperature present in the solid fuel burning furnace does not exceed a predetermined threshold within a given period of time, a relay is rendered operational to switch in the fluid fuel furnace. Additional comparators and digital logic circuitry is used to control the rate of burning of the solid fuel by modulating the on/off condition of the draft inducing blower.