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Mobile ViewHEATING SYSTEMS AFUE DEFINITION, RATINGS AGE of CHIMNEYS & FIREPLACES AGE of AIR CONDITIONERS & HEAT PUMPS AGE of FOUNDATION MATERIALS AGE of FRAMING MATERIALS AGE of FLOORING MATERIALS AGE of ELECTRICAL WIRING AGE of HEATERS, BOILERS, FURNACES AIR CONDITIONING & HEAT PUMP SYSTEMS AIR FILTERS for HVAC SYSTEMS AIR FILTERS, OPTIMUM INDOOR CONTINUOUS BLOWER FAN OPERATION AIR FILTER EFFECTIVENESS FIBERGLASS & AIR FILTERS SOURCES FOR AIR FILTERS ANODES & DIP TUBES on WATER HEATERS ANTI SCALD VALVES APPLIANCE EFFICIENCY RATINGS ASBESTOS IDENTIFICATION IN buildings BACKDRAFTING HEATING EQUIPMENT BACKFLOW PREVENTERS BAROMETRIC DAMPERS BASEBOARD HEAT BIOGAS PRODUCTION & USE BLEVE EXPLOSIONS BLOWER DOORS & AIR INFILTRATION BLOWER FAN CONTINUOUS OPERATION BLOWER FAN OPERATION & TESTING BLUE vs YELLOW COMBUSTION FLAMES BLUERAY Recall BOILERS, HEATING BOILER CHEMICALS BOILER COMPONENTS & PARTS BOILER CONTROLS & SWITCHES BOILER LEAKS CORROSION STAINS BOILER LEAKS, HOW TO LOCATE BOILER NOISE SMOKE ODORS BOILER OPERATING PROBLEMS BOILER OPERATION DETAILS BOILER PRESSURE & TEMPERATURE SETTINGS BOOKSTORE - InspectAPedia BUILDING SAFETY HAZARDS GUIDE CAPACITORS for HARD STARTING MOTORS CARBON DIOXIDE - CO2 CARBON MONOXIDE - CO CHIMNEY INSPECTION DIAGNOSIS REPAIR CHIMNEYS & Flues - Asbestos Transite Pipe CHINESE DRYWALL HAZARDS CIRCULATOR PUMPS & RELAYS COOL OFF HEAT, Thermostat Switch COMBUSTION AIR COMBUSTION AIR for TIGHT buildings COMBUSTION GASES & PARTICLE HAZARDS COMBUSTION PRODUCTS & IAQ COMPLETE COMBUSTION, Stoichiometric CREOSOTE FIRE HAZARDS CONDENSING BOILERS/FURNACES CONDENSING BOILERS/FURNACES DAMAGE CONVECTOR HEATERS - HYDRONIC COILS DEFINITION of Heating & Cooling Terms DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP DIAGNOSE & FIX HEATING PROBLEMS-BOILER DIAGNOSE & FIX HEATING PROBLEMS-FURNACE DIRECT VENTS / SIDE WALL VENTS DIRECTORY of OIL TANK EXPERTS DRAFT HOODS - gas fired DRAFT MEASUREMENT, CHIMNEYS & FLUES DRAFT REGULATORS, DAMPERS, BOOSTERS DUCT SYSTEM & DUCT DEFECTS AIR FILTERS for HVAC SYSTEMS ALLOY SYSTEMS FLEXDUCT ASBESTOS HVAC DUCTS ASBESTOS PAPER on DUCTWORK ASBESTOS TRANSITE DUCTWORK BALANCING AIR DUCT FLOW DUCT & AIR HANDLER ODORS DUCT INSULATION, Asbestos Paper DUCT DAMAGE, MECHANICAL DUCT INSULATION - Asbestos Paper DUCT ROUTING & SUPPORT DUST CONTAMINATION FROM HVAC? FIBERGLASS DUCT, RIGID CONSTRUCTION FIBERGLASS HVAC DUCTS FIRE DAMPERS in DUCTWORK FLOOD DAMAGE in DUCT WORK GOODMAN GRAY FLEXDUCT INCREASING RETURN AIR LEAKY DUCT CONNECTIONS LOCATION OF REGISTERS & DUCTS MOLD in AIR HANDLERS & DUCT WORK NOISES in DUCT SYSTEM ODORS in AIR HANDLERS & DUCT WORK OWENS CORNING FLEXDUCT OWL FLEXDUCT RETURN AIR REGISTERS & DUCTS SOUNDPROOFING for DUCTWORK SUPPLY DUCTS & REGISTERS TRANSITE PIPE AIR DUCTS UNDERSIZED RETURN DUCTS UNSAFE DUCT OPENINGS VIBRATION DAMPENERS WATER & ICE IN DUCT WORK WET CORRODED DUCT WORK ZONE DAMPER CONTROLS DUST CONTAMINATION FROM HVAC? ELECTRIC HEAT, DIAGNOSIS, REPAIR ELECTRIC MOTOR DIAGNOSTIC GUIDE ELECTRIC MOTOR OVERLOAD RESET SWITCH ELECTRICAL POWER SWITCH FOR HEAT EVAPORATIVE COOLING SYSTEMS FAN, AIR HANDLER BLOWER UNIT FAN AUTO ON Thermostat Switch FAN, COMPRESSOR/CONDENSER UNIT FAN CONVECTOR HEATERS - HYDRONIC COILS FAN LIMIT SWITCH FAN NOISES FILTERS, AIR for HVAC SYSTEMS FILTERS, OIL on HEATING EQUIPMENT FIRE SAFETY CONTROLS FIREPLACES & HEARTHS FLAME COLOR, BLUE vs YELLOW COMBUSTION FLOODED HEATING EQUIPMENT REPAIR FLOODED WATER HEATER REPAIR FLUE SIZE SPECIFICATIONS FLUE VENT CONNECTORS FREEZE-PROOF A BUILDING FUEL OIL TYPES & CHARACTERISTICS FUEL UNIT, HEATING OIL PUMPS FURNACES, HEATING FURNACE CONTROLS & SWITCHES BACKDRAFTING HEATING EQUIPMENT CAD CELL RELAY SWITCH DIAGNOSE & FIX FURNACE DRAFT HOODS DRAFT REGULATORS ELECTRIC MOTOR OVERLOAD RESET SWITCH ELECTRICAL POWER SWITCH FOR HEAT FAN AUTO ON CONTROLS FAN LIMIT SWITCH FAN LIMIT SWITCH TROUBLESHOOTING FAN MOTOR START CAPACITORS FIRE SAFETY CONTROLS HEAT EXCHANGER CLEANING HEAT EXCHANGER LEAKS Reset Switch - Primary Control Reset Switch - electric motors SPILL SWITCHES STACK RELAYS THERMOSTATS, HEATING / COOLING ZONE DAMPER CONTROLS FURNACE EFFICIENCY, HIGH vs MID FURNACE HEAT EXCHANGER LEAKS FURNACE OPERATION DETAILS FURNACE OPERATING TEMPERATURES GALVANIC SCALE & METAL CORROSION GAS BURNER Flame & Noise Defects GAS FIRED WATER HEATERS GAS PIPING, VALVES, CONTROLS GAUGES ON HEATING EQUIPMENT GEOTHERMAL HEATING SYSTEMS HEAT EXCHANGER LEAKS HEAT LOSS in buildings HEAT LOSS DETECTION TOOLS HEAT LOSS INDICATORS HEAT LOSS PREVENTION PRIORITIES HEAT LOSS R U & K VALUE CALCULATION HEAT PUMPS, DiAGNOSIS, REPAIR HEAT TAPES & CABLES on Roofs for Ice Dams HEATING COST FUEL & BTU Cost Table HEATING COST SAVINGS METHODS HEATING LOSS DIAGNOSIS-BOILERS HEATING LOSS DIAGNOSIS-FURNACES HEATING OIL CLOUD WAX GEL POINT HEATING OIL EXPOSURE HAZARDS, LIMITS HEATING OIL - OLD, USEABLE? HEATING OIL PIPING TROUBLES HEATING OIL SHELF LIFE HEATING OIL SLUDGE HEATING OIL USAGE RATE HEATING SMALL LOADS HEATING SYSTEM INSPECT DIAGNOSE REPAIR HEATING SYSTEM NOISES HEATING SYSTEM SERVICE & MAINTENANCE HEATING SYSTEM TYPES HIGH EFFICIENCY BOILERS/FURNACES HOT WATER HEATERS HOT WATER IMPROVEMENT INSULATION INSPECTION & IMPROVEMENT LP & Natural Gas Safety Hazards MANUALS & PARTS GUIDES - HVAC MIXING / ANTI-SCALD VALVES MOTOR OVERLOAD RESET SWITCH Natural Gas Combustion Products NO HEAT - BOILER NO HEAT - FURNACE NOISE / SOUND DIAGNOSIS & CURE NOISE AIR CONDITIONER / HEAT PUMP NOISE, DUCT VIBRATION DAMPENERS NOISE, HEATING SYSTEMS NOISE, PLUMBING NOISE, WATER HEATER ODORS GASES SMELLS, DIAGNOSIS & CURE ODORS FROM HEATING SYSTEMS OIL BURNERS OIL BURNER FUEL UNIT OIL BURNER INSPECTION & REPAIR OIL BURNER NOISE SMOKE ODORS OIL BURNER NOZZLE & ELECTRODES OIL BURNERS, RETENTION HEAD OIL BURNER SOOT & PUFFBACKS OIL FILTERS on HEATING EQUIPMENT OIL FILTER MISSING OIL FUEL TYPES & CHARACTERISTICS OIL & GAS PIPING OIL LINE CLOGGING FIX OIL LINE QUICK STOP VALVES OIL LINE SAFETY VALVES OIL ODORS, LEAKY OIL TANK PIPING OIL PUMP FUEL UNIT OIL SPILL CLEANUP / PREVENTION OIL TANKS PLASTIC HEATER VENT PULSE COMBUSTION HEATERS PASCAL CALCULATIONS RADIANT BARRIERS RADIANT HEAT RADIANT HEAT Floor Mistakes to Avoid RADIANT HEAT TEMPERATURES RADIANT SLAB FLOORING CHOICES RADIANT SLAB TUBING & FLUID CHOICES RADIATORS RELIEF VALVES - TP Valves on Boilers RELIEF VALVES - STEAM TP VALVES RELIEF VALVES - Water Heaters RELIEF VALVES - TP Valves on Boilers RELIEF VALVES - STEAM TP VALVES RELIEF VALVES - Water Heaters RELIEF VALVES - Water Tanks Reset Switch - Heater Primary Control Reset Switch Broken - Quick Repair Reset Switch - Electric Motors Reset Switch - Stack Relays SAFETY HAZARDS & INSPECTIONS SAFETY HAZARDS GUIDE SAFETY, HEATING INSPECTION SAFETY,HOME HEATING TIPS Safety Recalls, Chimneys, Vents, Heaters SOLAR HEATING SYSTEM DESIGNS SOLAR HOT WATER HEATERS SOOT on OIL FIRED HEATING EQUIPMENT SPILL SWITCHES - Flue Gas Detection SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS STACK RELAY SWITCHES STAIN DIAGNOSIS on BUILDING INTERIORS STEAM HEATING SYSTEMS TANKLESS COILS THERMAL EXPANSION of MATERIALS THERMAL MASS in buildings THERMAL TRACKING & HEAT LOSS THERMOSTATS, HEATING / COOLING THERMOSTATIC EXPANSION VALVES Transite Pipes, Chimneys & Flues WINTERIZE A BUILDING WOOD, COAL STOVES & FIREPLACES WOOD STOVE SAFETY ZONE VALVES More Information |
Warm air furnace installation, troubleshooting, repair guide: this article series answers just about any question about forced air or warm air furnace central heating system troubleshooting, inspection, diagnosis, and repairs in residential buildings and homes. We explain how furnaces work, what controls and settings are used, what goes wrong, and how to fix it. This page is the starting point for our series of heating furnace diagnosis and repair articles. The key heating furnace components are introduced here at FURNACES, HEATING. InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers nor with topics or services discussed at this website.© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website. Warm Air Furnace Inspection, Diagnosis & Repair - where to start?If you have no heat, see HEATING LOSS DIAGNOSIS-FURNACES. You can also continue your heating furnace diagnostic procedures with the articles at page left headed under FURNACE CONTROLS & SWITCHES. If your furnace is fired by an oil burner, you can go directly to those diagnostics at OIL BURNER INSPECTION & REPAIR. Gas burners are discussed at GAS BURNER Flame & Noise Defects.The basics of how furnaces work can be read at FURNACE OPERATION DETAILS.The Sketch at page top courtesy of Carson Dunlop At this website we describe the basic components of a home heating system, how to find the rated heating capacity of an heating system by examining various data tags and components, how to recognize common heating system operating or safety defects, and how to save money on home heating costs. We include product safety recall and other heating system hazards. First make sure you understand what type of heating system is installedIf you don't know what kind of heat your building uses, we explain how to figure out the answer in more detail at HEATING SYSTEM TYPES. These photos will help you determine what kind of home heating system you have. Here we're showing heating equipment just as you'll see it in your home, with all of the access covers and panels in place. Articles at this website offer lots more detail including photos of individual heating system controls and components along with explanatory text.
The heated air is being heated by a gas, oil, or electric furnace, or perhaps by a heat pump or a geo-thermal system then your heat is provided by a warm air furnace (sketch at page top, for example) Cooler air (hopefully also from the same occupied space) flows back to the furnace through one or more air returns and ducts into the furnace return air plenum from which it enters the furnace itself to be re-heated. Some older warm air systems (illustrated below) are less sophisticated and may have no ductwork at all, and worse, may heat cold air from the basement and send it one-way into the occupied spaces of the home. What's the Difference Between Forced Hot Air Heat and Gravity Hot Air Heat?Your heating furnace may located in a basement, in a crawl space, in an attic, or even in an outdoor utility closet or an attached garage. In all cases, some heating equipment (oil, gas, coal, wood, geothermal, electric, solar) is used to transfer heat to air that is then delivered to the occupied space of the building. Illustration of Simple Gravity Furnaces using a Floor Register (Ductless Warm Air)
Popularly called a "gravity furnace" (cold air falls by gravity, and warm air defies gravity by rising), you will see only two "pipes" or ducts on the unit. A flue gas exhaust flue (the smaller diameter steel "pipe" that exits near the bottom left of the gravity furnace and connects to a brick chimney in our photo - and that larger diameter round duct at the top center of the gravity furnace. That large round warm air supply plenum or duct delivered warm air into the building through a large floor grate in the first floor above. Our arrows show the direction of air flow through this gravity furnace. In this photo we can't see the cool air intake but almost certainly it's at the bottom of the unit and is in this horribly inefficient unit, is taking cold wet basement air and heating it up before sending it upstairs. We do see a little of this furnace's repair history - that abandoned motor on the floor in the bottom center tells us that an oil burner was installed and had to have a motor replacement. Warm air rose from this gravity furnace upwards from the first floor grate into the rest of the building also by convection (or "gravity") flowing up a stairwell, or upstairs through registers cut in the first floor ceilings. How to Spy on your Parents Through the Gravity Heat Registers
But now let's be honest - we don't know for sure if the air register at left is connected to ductwork or if it's just letting warm air rise by "gravity" (we say "convection") from a floor below. It's easy to figure out however. Just open the louvers and look through the grating. If you find yourself looking into a duct, typically full of trash and debris in an older home, it's connected to ductwork. If you find that your can see right into a room below, this is a simple gravity or convection register. When the author (DF) was a boy, we used to spy on our parents and their friends by peering down at them through a register like this after we had been sent upstairs to bed. They were not up to much besides drinking, talking about stuff we couldn't understand, and playing canasta. Illustration of Octopus Furnaces that Added Warm Air DuctsOctopus furnaces (illustrated below) added warm air ducts that conducted air directly to different areas of the building. You can see at below left why the heater was called an "octopus" furnace. It may not have always had the eight arms of an octopus but it sure looks like one, with those ducts waving all around. At below left you can also see the stack relay (black rectangular control) on the exhaust flue of this octopus furnace.
At in both of the above photos and enlarged at above right we illustrate that white paper-like duct wrap that was just about always an asbestos paper material. On the octopus furnace at above right you can also see a rectangular heating control switch near the top of the furnace. Those black Tee-shaped controls visible on the ducts themselves are manual duct dampers that allowed the occupants to balance warm air flow among different areas of the building. Examples of Modern Forced Warm Air Furnaces
Depending on their physical position a furnace may be an upright unit or a horizontal unit suited for low basements or crawl space installation. Heating system air flow direction determines whether we call the vertical air handler an upflow unit (cool air enters at the bottom) or a downflow unit (cool air enters at the top of the unit). Our upflow/downflow furnace illustration at left was provided courtesy of Carson Dunlop Associates. Below at left is an up-flow high efficiency gas fired furnace that we installed. Air enters that silver plenum at the base of the unit and flows upwards through an air filter, blower assembly, heat exchanger and supply plenum into supply ductwork. Our arrows indicate the direction of air movement through the upflow furnace.
At below right is a horizontal furnace. We guess that return air is entering at the right end of the unit because those flex ducts are larger than the smaller flex duct headed up from a (not visible) connection to the supply plenum at the left end of the unit. A look inside through the blower compartment access door on the other side of this unit would answer the question. See FURNACE CONTROLS & SWITCHES and for details about how furnaces work and their controls, see FURNACE OPERATION DETAILS.
How does a Warm Air Heating Furnace work?
Continue with Warm Air Heating Furnace System Diagnosis & RepairIf you have no heat, see HEATING LOSS DIAGNOSIS-FURNACES. You can also continue your heating furnace diagnostic procedures with the articles at page left headed under FURNACE CONTROLS & SWITCHES. If your furnace is fired by an oil burner, you can go directly to those diagnostics at OIL BURNER INSPECTION & REPAIR. Gas burners are discussed at GAS BURNER Flame & Noise Defects. Frequently Asked Question about warm air heating furnace system diagnosis & repairQuestion: My furnace gas burners go on but the blower does not start and then the flame goes off. What's wrong?
Reply: as a safety feature on furnaces, the fan limit switch turns off the burner if the blower does not startRobert, if the furnace blower fan will not start, the limit switch on your furnace will turn off the burner in order to avoid overheating and damaging the heat exchanger. You'll need to inspect and fix the blower fan problem. If your furnace blower uses a drive belt to connect the fan to the driving motor check that the belt is in place and not slipping. Other blower fans use a direct drive motor whose shaft spins the fan assembly. IN either case check that the motor is starting; Questions & Answers regarding this articleQuestions & answers about how to buy, install, maintain, and fix warm air heating furnaces, ductwork, and controls Ask a Question or Search InspectAPediaHTML Comment Box is loading comments...
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