Gas Furnace Parts and Components

The anatomy of a gas furnace includes three groups of components.

Internal furnace parts allow the furnace to produce and distribute heated air in heat mode and cooled air in AC mode. These parts include the ignitor, gas valve, burner, blower, sensors, AC coil and electrical components.

External components assist the furnace in providing heating and air conditioning to your home. These include ductwork, thermostat and zoning equipment.

Indoor air quality components include the air filter and non-essential extras like a humidifier, dehumidifier or UV germicidal light.

Each group is fully discussed on this page to give you a clear understanding of how your furnace and related components function, troubleshooting tips and potential furnace repair costs plus where to buy furnace repair parts.

Links on the page take you to more complete information about specific furnace parts and components.

Gas Furnace Parts

A range of gas furnace parts are essential to the effective and safe working of your furnace.

As you peruse this gas furnace parts section, you will find definitions, what each part does, common problems, replacement costs and whether it can be switched out DIY or better handled by a pro. If you DIY, where to buy furnace parts is discussed.

Blower Motor

The blower motor is the motor that drives the blower fan. The blower pushes treated air, heated or cooled, out of the furnace into the ductwork while pulling untreated air into the furnace to be treated.

The cost of blower motor replacement is $450 to $1,500. The cost of the part is determined by the horsepower of the motor, whether it is an affordable PSC motor or a more expensive ECM motor and whether it is a single speed, multi speed or variable speed motor. The accessibility of the blower motor within the furnace affects repair cost when an HVAC technician is hired for the job.

Common blower motor problems include worn bearings and age-related failure. A buildup of dirt that impedes the motor may eventually cause it to fail.

Blower motor replacement difficulty is moderate for those with good DIY skills and the tools needed to remove the old motor and install a new motor. If you do it yourself, find a guide on how to replace the furnace blower motor DIY to assist you in the process.

Capacitor

Furnaces have two capacitors or one dual capacitor. The start capacitor stores energy while the furnace is running to provide the extra power necessary to start the motor the next time. It is necessary because the motor requires 3-5 times more energy to start than it does to run.

The run capacitor provides a steady flow of electricity to the motor as it runs.

Furnace capacitor replacement cost is $35 to $200. Cost depends on the price of the part, usually $35 to $70, and whether you DIY or hire a technician for replacement.

Capacitors can burn out with age or with an electrical surge. Replacing a furnace capacitor is one of the easier DIY repairs, though many homeowners call a professional to ensure proper troubleshooting of the issue and to make the repair.

Coil

If you have central air conditioning, then your furnace houses the evaporator coil. Refrigerant flows between the evaporator coil and outdoor condensing coil. Heat is absorbed indoors and carried outside to be dispersed.

Leaks are the primary repair issue with coils. Corrosion at connections and accidentally crimped lines are the primary cause of leaks. Repair is sometimes possible, but replacement is a longer lasting fix.

Evaporator coil replacement cost is $750 to $1,400 with the part costing $350 to $900. Because refrigerant is involved and a refrigerant handling certification is required, the job of replacing a coil is handled by a professional.

Heat Exchanger

The heat exchanger is a steel component that super-hot combustion gasses flow through. Heat is transferred from the heat exchanger to air being circulated over it and through ductwork.

Gas furnace heat exchanger replacement cost is $1,000 to $4,500. The cost is high even if the heat exchanger is under warranty and the part is provided at no charge. The labor cost to replace it is still very high because the furnace must largely be disassembled. It is a difficult repair, and warranties do not cover labor.

Because of the cost and age of a furnace when the heat exchanger is prone to fail, most homeowners decide to replace the furnace instead of making the repair.

Common heat exchanger problems are corrosion holes caused by acidic combustion byproducts or age and separation of the crimps or welds holding the exchanger together.  

Flame Sensor

The flame sensor confirms that the furnace burner is lit. If the gas valve opens but the gas doesn’t ignite, it presents the risk of a gas explosion. If the flame sensor does not sense a flame, it will signal the control board to shut the gas valve and abort the cycle. It’s also possible that if there is a flame problem, and it isn’t as hot as it should be, the sensor might shut down the cycle. Flame colors indicate whether the flame is burning as hot as it should be. 

The cost to replace a flame sensor is $15 to $25 if you do it yourself. This is a fairly easy DIY repair. The sensor plugs into the circuit board and is held in place with a single screw. Hiring an HVAC pro for the job runs a total of $75 to $150.

Flame sensors get dirty from soot. Cleaning the sensor with an emery cloth will ensure it is able to sense flame and won’t shut down the furnace when it shouldn’t. Over time, the sensor or its wiring can fail due to being constantly subjected to heat.

Pressure Switch

The furnace pressure switch monitors pressure within the burner box to ensure that air is flowing out the vent. If the vent is blocked, negative pressure is produced, and the pressure switch will shut down the heat cycle. This prevents combustion gasses containing carbon monoxide from entering your home.

Furnace pressure switch replacement costs $175 to $300 when a licensed HVAC technician does the work. Doing it yourself is quite easy, and the part costs $15-$25.

Pressure switches wear out with age. The tubing can crack, which prevents the switch from doing its job, and the part must be replaced. It is fairly easy to troubleshoot and test a furnace pressure switch to determine whether it is bad. 

Limit Switch

The furnace limit switch is also called the high limit switch. It monitors the temperature within the plenum connected to the furnace. If the furnace overheats because the hot air isn’t being pushed into the ductwork, the switch will shut down the furnace.

A limit switch lasts 10-15 years but can eventually fail due to heat exposure. The cost of a furnace limit switch is less than $25. And it is a fairly easy DIY repair. If you hire a pro for the work, the total cost is $180-$300.

Inducer Motor

A gas furnace inducer motor or draft inducer motor is the first motor to start in a heating cycle. Its job is to ensure that the furnace is venting and that dangerous exhaust gasses will leave your home. If the furnace vent is blocked, the pressure switch will shut down the cycle.

The inducer motor can wear out with time or be damaged by an electrical surge. Furnace draft inducer motor replacement cost is $100 to $550 for the part and another $125 to $300 for labor.

Pilot Light

A furnace pilot light is a standing flame that ignites the gas when it is released from the valve. Furnaces are no longer manufactured with pilot lights, and very few furnaces with one are still in use.

If the pilot light won’t stay lit, the most common reason is that the gas orifice on it is dirty or clogged. Cleaning might help, or the pilot light assembly might need replacing. Because the job includes a gas connection, this work is best left to a certified technician. Pilot light replacement cost is $190 to $300.

Condensate Pump

The condensate pump drains water from the furnace that is a byproduct of high-efficiency combustion. It also pumps out water that condenses on the indoor coil during an AC cycle.

Common furnace condensate pump problems include getting clogged, which can impede the working of the float within the pump that signals it to turn on or off. As a result, the pump might not run – or might not stop running. Either issue can cause pump failure.

The cost to replace a furnace condensate pump is $275 to $500 for the part and pro installation. If you’re handy and have the tools, DIY pump replacement starts at about $60 to $100.

Condensate Drain

As noted, there is a need to have a drain condensate with high efficiency gas furnaces. The drain allows this to happen. The drain can work by gravity sending water to a floor drain or it can be attached to a condensate pump for pumping it up and out of the house.

When the drain gets clogged, condensate leaks are common.

The cost to clear a clogged condensate drain is $125 to $200 for the service call. If the drain must be replaced, the part runs about $15 to $30. Clearing a clogged condensate drain can be a messy job, but it is doable if you know how to use a powerful shop vac or a plumber snake to do the job.

Circuit Board

The circuit board, control board and motherboard all refer to the electrical board that controls the furnace.

Common circuit board problems include burning out with age or a power surge, solders coming apart and individual parts on the board failing. You can know if your furnace control board is bad if the furnace won’t work at all or fails to progress through checking error codes on the furnace or testing it with a multimeter.

The board can’t be repaired; it must be replaced at a cost of $200-$400 for the board and a total cost of $375 to $700 for pro replacement.

Ignitor (Igniter)

Furnace ignitor problems include wearing out with age, cracking and failing due to heat exposure and dirt buildup that causes them not to work.

Knowing how to tell if your furnace igniter is bad begins with setting the thermostat to call for heat. If the inducer motor starts, but the furnace doesn’t fire, a bad igniter is one potential cause. You can also test the part using a multimeter to check voltage going through it.

Furnace ignitors are inexpensive and fairly easy to replace. If you DIY, the part will cost less than $40. The part plus replacement runs $100 to $200 if you hire a furnace pro.

Gas Valve

The furnace gas valve opens to release gas when signaled by the control board. Single stage valves open fully every time. Two-stage and variable gas valves open in stages to produce various heating levels.

In time, the gas valve will wear out or become clogged with dirt to the point it doesn’t function properly. While cleaning might work, more often the valve is replaced.

Furnace gas valve replacement cost is $415 to $850 or more for the part and installation. Most homeowners hire a licensed HVAC contractor to replace the valve because of the importance of safety when working with gas.

Gas Furnace Components

Your gas furnace is part of your complete HVAC system. The system requires ductwork to circulate air. And it might be fitted with one or more extra components that improve the climate in your home.

Here are common gas furnace components, what they do, when you should consider adding one of the extras and what the cost will be.

Ductwork

The ductwork is attached to your furnace by pieces called plenums. Air is forced through the ductwork by the blower.

Ducts are divided into supply air and return air sides. Supply ductwork carries treated air, either heated or air conditioned, to the rooms in your home. Return air ductwork carries air from the rooms back to the furnace to be treated.

The cost to install ductwork when a home is being built is $1,500 to $3,000 based on home size, layout and location of the furnace. Ductwork replacement cost in an existing home can be $2,000 to $5,000 or more because the work is more difficult.

Zoning System

A furnace zoning system uses dampers on ducts that can be opened, closed or partially closed to control the flow of air through each branch of ductwork. Dampers can be manual or controlled by motors.

Have a zoning system installed if you have a large home and don’t prefer to heat and cool all rooms to the same level all the time.

The pros and cons of zoning systems include the ability to regulate heating and cooling in each zone or room, but at a cost of $2,000 or more. Cost is based on using motors or not and the number of zones.

Air Purifier

There are several types of furnace air purifiers including HEPA filters, ionic devices and electrostatic purifiers. They remove impurities from the air circulating in your home.

If you or anyone in your household has breathing issues or if you live where allergies are severe, consider adding a whole house air purifier to your furnace.

The cost of a furnace air purifier is $750 to $3,600 depending on the type and installation factors.

Humidifier

A furnace humidifier is a whole house humidifier used to raise the level of humidity in your home during the heating season. A humidifier makes the air more comfortable and reduces dry skin, irritated eyes and breathing passages and the hassle of electrostatic electricity.

Add a furnace humidifier if the air in your home becomes uncomfortably dry during winter. The cost of a whole house furnace humidifier is $500 to $1,500 based on the type you choose and who installs it, you or an HVAC technician.

Dehumidifier

A furnace dehumidifier removes excess moisture from the air in your home. The device is installed in ductwork near the furnace.

Homes in humid regions of the country, and levels of a home below grade, are susceptible to mold and mildew. If that applies to your home, consider adding a furnace dehumidifier to reduce harmful humidity.

The cost of a whole house dehumidifier is $1,000 to $2,700 based on the size and type of dehumidifier you purchase. The cost includes installation.

UV Lights

UV lights or UV germicidal lights are installed inside the ductwork to kill harmful bacteria and viruses in the air.

Consider installing germicidal UV lights for your HVAC system if you have children or older adults in your home – or anyone with a compromised immune system or breathing trouble.

The cost of HVAC UV lights added to your HVAC system is $160 to $695 when a furnace contractor installs the equipment.

Thermostat

Your HVAC thermostat regulates the temperature in your home and controls whether the system is in Heat or Cool mode. It can also be set to Fan, which runs the fan full-time.

Simple digital thermostats are the most affordable. Popular nest, ecobee, Lux and Honeywell thermostats are mid-priced. Communicating thermostats from the major brands like Lennox, Trane and Carrier are the costliest.

Reasons for buying a new thermostat include having a new HVAC installed, wanting a programmable thermostat to control heating and AC costs or because you want features such as artificial learning, filter change notification or geofencing.  

Prices range from $40 to $800 for the thermostat plus $75 to $125 to have it installed by an HVAC technician.

Filter

Your furnace filter removes dust, pet dander and hair from the air being pulled into your furnace. It protects your furnace from dirt and makes the air in your home healthier for breathing.

Change your furnace filter every 1-3 months depending on how heavily your furnace runs. In very cold climates and a dusty environment, changing the filter monthly is necessary. A dirty filter impedes furnace performance and airflow. It causes the furnace to work extra hard or overheat, and both can cause mechanical failure.

Furnace filters cost $5 to $40 depending on the MERV or other rating for filtration – what size particles it filters.

Where Can I Purchase Furnace Parts?

You can purchase furnace parts from local hardware and home improvement stores, local HVAC parts distributors and from many online retailers.

Local chain stores that sell some furnace parts include Ace, True-Value, Lowes, Menards and Home Depot.

Online furnace parts sellers include HVAC Direct, Repair Clinic, Furnace Part Source and Reliable Parts. Amazon sells some parts too.

Your options are to buy OEM parts made by the furnace manufacturer and made specifically for your furnace or to buy universal parts made by parts manufacturers. The best way to ensure getting the right part is to order furnace parts by model number. 

Parts distributors in your area serve HVAC contractors, though some will sell direct to the public too. These furnace parts suppliers are your best option for finding parts made specifically for your furnace brand such as Trane, Goodman, Carrier, Lennox, Rheem, Ruud, Heil, Nordyne, Ducane, York or Coleman.

Who Makes Furnace Parts?

There are quite a few parts manufacturers that make parts that can be used in a range of brands. 

Furnace replacement parts are made by Honeywell, Emerson, Carlyle, Riello, Danfoss, and Copeland.