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Gas Heat Unit 31

Gas Heat Key Terms

Automatic Combination Gas Valve A gas valve for gas furnaces that incorporates a manual control, gas supply for the pilot, adjustment and safety features for the pilot, pressure regulator, and the comtrols for and the main gas valve
Bimetalic Safety Device A pilot safety utilizing a bimetal stirp heated by the pilot flame. When the strip is hot a contact is closed energising the gas safety valve.
Burners Gas combustion takes place at the burner. Mixes air and gas for proper combustion.
Carbon Dioxide A by-product of natural gas combustion that is not harmful but can cause health problems.
Carbon Monoxide A poisonous, colorless, odorless,tasteless gas generated by incomplete combustion.
Combustion A reaction called rapid oxidation or burning produced with the right combination of a fuel, oxygen, and heat (ignition source).
Combustion Air Air (oxygen) used in the process of burning a fuel.
Condensing-Gas Furnace A furnace with a condensing (secondary finned)heat exchanger that condenses moisture from the flue gases,capuring latent heat of condensation resulting in greater efficiency.
Continuous Retry A gas ignition control that will keep trying to establish a pilot and shut off after each unsucessful ignition sequence.
Dew Point The exact temperature at which moisture begins to form, condensate.
Diaphragm Gas Valve Uses gas presure to open and close the main gas valve. Pressure above the diaphragm closes the valve.
Dilution Air Excess air after combustion and usually enter at the draft hood at the end of the heat exchanger.
Direct-Spark Ignition (DSI) A system that ignights the main burner directly.
Direct Vented A sealed venting system, pulling the air in from outside for combustion and venting the exhaust air to the outside.
Downflow Counterflow, the air is forced down through the furnace usually with the blower above and the heat exchanger below. Sometimes multi position furnaces.
Dual-In-Line Pair (DIP) Switch On off switches used to adjust sequencing on printed circuit boards.
Dual-Rod (Remote) Sensing Uses a separate igniter and flame-sensing rod or electrode.
Excess Air Combustion air and dilution air combined make excess air less excess air the lower the dew point
Fan Switch Device to automaticaly cycle a fan on and off. Operated by temperature, time & temp, or time
Flame Impingement When the flame touches anything it is not intended to touch, usually causing soot and or poor combustion
Flame-Proving Devices Device in a gas or oil furnace to ensure that there is a flame so that excess fuel will not be released causing an unsafe condition.
Flame Rectification In a gas furnace, the flame changes the normal current to direct current. The control modual will only allow the gas valve to be opened when direct current is sensed.
Forced Draft Use a combustion blower mounted at the inlet of the heat exchanger pushing or blowing combustion gases through the heat exchanger causing a positive pressure in the Heat exchanger.
Gas Furnace Burner Inshot, upshot, ribbon, slotted, drilled port, are types of burners used in gas furnaces.
Gas Regulator Maintains proper manifold gas pressure by reducing main line to stated manifold pressure, supplying proper input to the appliance.
Gas-Type Solenoid Valve is normally closed and opened by energizing a solenoid coil causing the gas valve plunger to move, opening the valve.
Glow Coil Device that heats up to automatically reignite a pilot light if it goes out.
Hard Lockout Shutsdown or locks out the ignition control when no flame is sensed in a given period of time and must be reset by turning the power on and off.
Heat Exchanger Transfers heat from the flew gases to the room air, keeping the air-streams seperate, preventing combustion gas from entering the building.
Heat-Motor-Controled Valve A heating element(coil) heats up when energized causing a bimetal to expand opening the gas valve. Caution: this is a slow opening and closing valve.
High-Efficiency Gas Furnace Utilize more heat exchange surface and more airflow to increase efficiency, high efficiency furnaces vent with PVC pipe.
Hot Surface Ignition A silicon carbide or simular substance is placed in the gas stream and allowed to get very hot. When the gas impinges on the heated surface, immediate ignition should occur.
Horizontal Furnace A furnace that is layed on its side utilizing a horizontal air flow. Usually installed in a crawl space, atic or suspended from floor joists or rafters. See Multipositional Furnace
Ignition or Flame Velocity The rate at which the flame travels through the air and fuel mixture. The rates are different for each gas. The faster the rate the more explosive the gas.
Induced Draft A combustion blower is located on the outlet of the heat exchanger. The blower pulls the flew gases through the heat exchanger creating a negative pressure.
Inshot Burners A single port atmospheric burner used primarily with induced draft heat exchanges firing directly into the heat exchanger.
Integrated Furnace Controller(IFC) Controls some or all functions of the furnace, igniton, fan, fan cycles, fan speeds, A/C and accessory connections.
Interpurge Combustion Blower operates for a period of time between tries for ignition. Interpurge happens usually when the burner doesn't light and before the next try for ignition. Heat exchangers need to be purged of unburned gas and flue gas between cycles.
Limit Switch A normaly closed device designed to stop a piece of equipment before it does damage to itself or the surroundings,a high limit on a furnace or internal overload on a motor.
Liquid-Filled Remote Bulb includes a diaphram, a tube, and a bulb filled with a liquid, ussually mercury. The liquid in the bulb expands or contracts when heated or cooled, which moves the diaphram that is connected to a switch.
Liquified Petroleum (LP) Propane, Butane or a combination of these gasses kept under pressure until ready to use as a fuel.
Lockout Time period built into the ignition module for ignition to occur, if the time period is exceeded the module will go into soft or hard lockout.
Low-Boy A furnace with the supply and return opening on the top, about 4 ft high.
Manifold A device with multiple outlets or inlets controlled with valves or other devices. Typically control gases or liquids.
Manifold Pressure Pressure within a gas distribution header after the gas valve before the orifice.
Methane Natural gas, combustible hydrocarbon 90 to 95% pure.
Modulating Gas Furnace The gas valve (BTU), venter fan speed, and the indoor blower motor speed are varied to match the BTU output of the furnace to the heating requirements for the conditioned space. Very efficient.
Multi-Poise(Multi-positional) Furnace Furnace designed to be installed in more than one application. Up-flow, Down-flow, Horizontal
Natural Gas A fossil fuel formed over millions of years from dead vegetation and animals that were deposited or washed deep into the earth. Methane
Non 100% Shut-Off when a flame is not sensed the main gas valve will shut off but the pilot gas will continue to flow, the ignition system will attempt to reestablish a pilot and main burner when safe.
Non-Direct Vented Un-vented combustion air is directly vented into conditioned space
100% Shut-Off The ignition system shuts off all gas and and locks off when a flame is not detected.
Orifice A small opening through which gas or liquids flow.
Postpurge Allows the combustion blower to run after each heating cycle to exhaust any fumes and unburned gas.
Prepurge Allows the combustion blower to run before each heating cycle to exhaust unburned gas and any residual fumes from the heat exchanger.
Servo Pressure Regulator A sensitive pressure regulator located inside a combination gas valve that senses the outlet or working pressure of the gas valve.
Single Rod (local) Sensing The spark ignition and flame sensing is done with one wire and one flame rod.
Smart Valve Combines the gas and ignition controls in one gas valve.
Soft Lock Very common ignition control, when flame is not detected the control will shut down and recycle itself to retry for ignition. Some will cycle several times and then hard lockout.
Spark-to Pilot(Intermittent Pilot)Ignition On a call for heat: the pilot and igniter are turned on by the ignition control, when the pilot is sensed the main burner is ignited, the system cycles off when temperature is reached.
Standing Pilot A continuously burning pilot flame, must use pilot safety device.
Thermocouple A device made of two unlike metals that generates electricity when there is a temperature difference from one end to the other. Have a hot and cold junction.
Thermopile A group of thermocouples connected in series to increase voltage output (500 to 750 mV),
Troubleshooting Flowchart Step by step procedures to follow when diagnosing a gas furnace problem, sequence of operation.
Up-flow Vertical air flow through a furnace, air enters the bottom or sides and is discharged out the top.
Upshot Burners Flame burns in an upward direction from the burner.
Variable Output Thermostat The signal coming out changes with the temperature
Venting Products of Combustion Water, CO2 AND CO are produced when gas is burned
Venturi A smooth tapered device used to increase velocity and mix air and gas in a gas burner.
Water Column (WC) Used to measure smaller preasure. The amount of pressure required to raise water in a tube one inch is 1 inch WC
Water Manometer A device (U-Tube) that uses a column water ina tube to to
Created by: tskipper