Abstract: A gas furnace responsive to a thermostat includes a thermal switch wired in series between the furnace power supply and the thermostat. A microprocessor connected to the thermal switch detects when the switch opens and closes, carrying out prearranged programs in response thereto. The thermal switch is mounted so that it opens when an over-pressure in the furnace draft system is detected, as evidenced by hot flue gasses passing over the thermal switch probe. The switch is allowed to cycle at least one time before the furnace is disabled. After a certain period of the time, the combustion cycle is reinitiated and the above steps are repeated if the thermal switch again resets.

Abstract: A gas furnace responsive to a thermostat includes a thermal switch wired in series between the furnace power supply and the thermostat. A microprocessor connected to the thermal switch detects when the switch opens and closes, carrying out prearranged programs in response thereto. The thermal switch is mounted so that it opens when an over-pressure in the furnace draft system is detected, as evidenced by hot flue gasses passing over the thermal switch probe. The switch is allowed to cycle at least one time before the furnace is disabled. After a certain period of the time, the combustion cycle is reinitiated and the above steps are repeated if the thermal switch again resets.

Abstract: A furnace is provided with a flame rollout protection system which operates through an existing excess-air control pneumatic circuitry to shut down the furnace in the event of a flame rollout condition. A fusible tube is attached at its one end to the pneumatic system and extends into an area which will be exposed to hot gases in the event of a flame rollout condition. A melting of the tube by the hot gases causes the pressure therein to drop to ambient pressure such that of the pneumatic circuitry responsively causes the furnace to shut down. The tube is also extended to pass through an area which will be exposed to hot gases in the event of a blocked vent in the furnace, thereby causing a similar shut down of the furnace.

Abstract: A method for adjusting the continuous speed of the blower of a heating and/or cooling system of the type including a thermostat having a mode selector switch which has at least one heating position, a cooling position, and an off position, a fan switch having an on position or state and an auto position or state, and a programmable control device responsive to the thermostat for generating speed select signals for use in setting the speed of the blower motor. The programmable control device is programmed or reprogrammed so that, when the mode selector switch is in its off position or when there is no call for heating or cooling at the thermostat, time dependent movements of the fan switch away from and back to its on position are recognized as requests for changes in the continuous speed of the blower motor.

Abstract: A compact gas combustion furnace includes a substantially rectangular casing having an interior defined by a plurality of compartments. A draft inducer is mounted above the heat exchanger compartment to allow a multipass heat exchanger to be used while allowing the furnace to be fitted within a mobile home closet. A transition box couples the horizontally disposed inlet of the inducer and the vertically disposed outlet side of the heat exchangers. In a preferable arrangement, the furnace includes a burner assembly utilizing a plurality of burners, each having an arcuate shape in relation to a corresponding plurality of heat exchangers, and thereby occupying a minimum of space without loss of efficiency.

Abstract: An apparatus senses the pressure changes in a collector box or relief box of a furnace due to changing wind conditions, and adjusts the gas flow accordingly. The apparatus controls the main gas valve of the furnace through a regulator loop. The regulator loop has a first port that communicates with a chamber below the main diaphragm of the valve, and a second port that communicates with a chamber above the main diaphragm. The regulator includes two diaphragms linked rigidly. A feedback pressure channel is connected to the collector box or the relief box, at one end, and to a feedback pressure tap at the other end. An increase in wind at the furnace vent causes changes in pressure in the collector box and the relief box. This change in pressure is delivered to the feedback pressure tap. When the pressure at the feedback pressure tap increases, the top diaphragm and the bottom diaphragm both move upward.

Abstract: In a two-stage furnace system, including a thermostat, at least one gas burner with a low and high-fire operating capability, an inducer fan having low and high speed operating settings, and a high-fire pressure switch, a method for handling the high-fire pressure switch being in an inappropriately open condition. The method has the steps of: determining whether the thermostat is issuing a call for high heat and, if it is, determining if the high-fire pressure switch is open. If the high-fire pressure switch is open, waiting a predetermined time, determining if the high-fire pressure switch is still open and, if it is, completing a furnace shutdown procedure, then initiating a normal shutdown, then an ignition sequence in high-speed inducer pre-purge mode, determining if the high-fire pressure switch remains open, and if so, running at least one gas burner in low-fire mode. If, while these steps are being performed, the high-fire pressure switch closes, running the system in high-fire mode.

Abstract: A two-stage induced draft furnace is operated at either high heat or low heat with the gas valve switched to high-fire or low-fire. High-fire and low-fire combustion pressure switches sense the collector box flue gas pressure and actuate respective solenoids of the gas valve. Under some conditions the inducer can produce sufficient negative pressure at low fire to prove the high fire pressure switch and cycle the burners on high fire. To prevent this, relay contacts are interposed between the high fire pressure switch and the gas valve solenoid to deny thermostat power to the high-fire solenoid whenever there is a call for low heat.

Abstract: A two-stage furnace is operable at a high fire full rate mode and at a low fire partial rate mode when there is a call for high heat or low heat, respectively. In order for the furnace to be less prone to vent gas condensate formation when operating at low fire, and to permit the heat exchanger and vent pipe to reach equilibrium as soon as possible on both low fire and high fire, a shorter blower-on delay is provided for high fire and longer blower-on delay is provided on low fire.

Abstract: A heating system with a hot water coil is provided with a variable speed blower whose speed is regulated in response to a sensed load in the system. Heat can therefore be added to the hot water by way of a simple burner system, with the required control being effected by selectively varying the amount of heat that is removed from the hot water by controlling the fan speed. When applied to a zone controlled system, the need for a bypass duct is obviated.

Abstract: In a gas furnace designed for operation with natural gas, the use of propane as a fuel is facilitated by increasing the inducer speed by a factor which is obtained by comparing the higher inducer speed necessary to bring down the heat exchanger temperature to an acceptable level, with the original lower inducer speed that had caused the temperature to exceed the allowed limit. Provision is made for electronically applying the multiplying factor by simply operating a gas selector switch.

Abstract: A gas fired condensing furnace comprising a multiple cell condensing heat exchanger is provided wherein each condensing heat exchanger cell has a condensing flow passage of serpentine shape formed from a single flat sheet metal blank. The condensing heat exchanger cell is formed to be compact in size and to minimize heating fluid side pressure drop therethrough. The condensing flow passage for each condensing heat exchanger cell provides high velocity fluid flow therethrough for increasing its heat transfer characteristics.

Abstract: A microprocessor control determines, in the course of initiating a heating cycle, whether the blower is operating in the continuous mode, and if it is, the control prompts the blower to be turned off prior to the ignitor being turned on. In this way, the blower and ignitor are never on at the same time and the instantaneous total current draw is limited to thereby reduce the occurrence of burned out fuses or circuit breaker trips.

Abstract: A furnace having the capability of operating its blower continuously is provided with means for automatically shutting off the blower at the beginning of a heating cycle and for resuming the operation thereof only after a predetermined time has elapsed to allow the heat exchanger to heat up to a temperature that exceeds the dew point of the flue gas, to thereby reduce the occurrence of cold spot corrosion in the heat exchanger. Provision is also made, in a two speed blower system, for operating at a lower speed during continuous mode and heating cycle operation, and for operating at the higher speed during the cooling cycles.

Abstract: The control system of an induced draft furnace includes a provision for turning on the inducer motor when a flame is sensed outside of the normal sequence of a heating operation. In particular, if the thermostat is in the off position when a flame is sensed, the inducer motor is turned on to ensure that sufficient combustion air is provided to the burner so as to forestall the occurrence of flame roll outs in the event that the gas valve is stuck in a closed position.

Abstract: A method and apparatus for maintaining the desired level of excess air in a two stage gas furnace system. Low and high pressure switches are placed across the heat exchanger and are successively closed, as the inducer motor accelerates during purging, when the pressure drop reaches the respective theoretically desired low and high firing pressure drop levels. As the switches are closed, the inducer motor speeds are sensed and recorded, with a ratio of the two then being calculated. After firing, the ratio is then directly applied to a desired high firing motor speed to obtain the desired low firing motor speed.

Abstract: Method and apparatus for maintaining excess air control in a gas furnace. A pressure switch is placed across a heat exchanger to indicate when, while accelerating the inducer motor speed during purging operation, the pressure drop reaches a predetermined level. When that occurs, the motor speed is sensed and recorded. When the furnace is subsequently fired, the desired inducer motor speed is obtained by modifying the recorded motor speed on a correction factor derived from empirical data obtained from a gas furnace operating under selective variable conditions.

Abstract: A furnace flue gas draft inducer outlet box assembly is provided for connecting an inducer housing to a vent pipe, and comprises a plurality of differently directed openings to allow the vent pipe to be connected thereto in one of a plurality of different orientations, thereby facilitating ease of installation of the furnace. When incorporated with a condensing furnace, the inducer outlet assembly further comprises a condensate collecting system for collecting a return flow of condensate formed in a vent pipe and for delivering the condensate out of the inducer housing to prevent contact with the inducer motor, wheel and the like.

Abstract: This invention relates to a method and apparatus for shutting down a combustion system when a pressure greater than atmospheric pressure is present in the flue pipe of the system. The apparatus comprises a connector means for connecting the flue pipe of the system with the surrounding atmosphere and a thermal switch which is in thermal contact with and responds to the gases within the connector means. The apparatus is especially useful as a safety device for shutting down an induced draft combustion system when the flue pipe of the system is blocked. Also, the apparatus can be used with a combustion system having a flue outlet vent which is also used as the outlet vent for another combustion system.