How To Adjust The Fan Speed On A Furnace?

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Adjusting a furnace’s fan speed can provide results like increasing or reducing warm airflow. Fine-tuning how this part functions can help provide comfortable temperatures in homes. But how can you adjust the fan speed of a furnace? We researched and consulted with different experts to give you the following answer.

Different furnace models often demand dissimilar steps for fan speed adjustments. However, most furnaces generally require users to change wires to fine-tune blower speeds. For instance, here’s the procedure to change a furnace’s fan speed with a PSC blower motor:

  1. Use a multimeter to measure the resistances of each speed wire.
  2. Connect the common wire to the neutral terminal of the furnace’s control board.
  3. Select your preferred wire with the warm temperature and connect it to the ‘heat’ port.
  4. Choose your ideal wire for the cold temperature and place it in the ‘cool’ port.

The steps to rewire an ECM furnace blower motor are fairly similar to fan adjustments for a PSC model. Keep reading as we talk about additional details on how to adjust the fan speeds on both furnace fan motor models. We’ll also tackle additional insights about furnace fans, such as replacement costs and ideal speeds.

Technician doing a system diagnose in the furnace system, How To Adjust The Fan Speed On A Furnace?

Are The Furnace Fan And Blower The Same Thing?

The furnace blower is also the heating system’s fan. It functions by blowing warm to the area in a home that needs temperature adjustments.

A furnace fan blower

Many furnaces come with blowers or fans attached to 1-horsepower or fewer motors. Although many fans can achieve 1,200-revolutions per minute (RPM) speeds, some models may spin at slower speeds, particularly those with fairly small heating frameworks.

For more information about these heating systems, read our post on the different types of furnaces and furnace filters.

How Do I Adjust The Fan Speed On My Blower?

Circuit control board of a home furnace

The steps to adjust the fan speed of a furnace's blower often depend on the unit's design. Homeowners and DIY enthusiasts can consult their owners’ manuals to check for the steps to adjust their specific units’ blower motors.

But keep in mind that you need to have a sufficient understanding of basic electronics before proceeding with this task. If you’re not confident with your current knowledge and skills in electronics, it might be best to contact certified technicians instead of doing this operation by yourself.

If you wish to continue, make sure to disconnect the furnace from its power source to reduce the risks of health hazards. Once you complete that precautionary measure, continue to learn the adjustment procedures for each type of furnace fan in the following section:

PSC Blower Motor Adjustments

PSC stands for permanent split capacitor, and it primarily functions by activating or deactivating the system’s electrical output. Blower motors using PSC frameworks typically don’t allow speed variances found at conveniently located buttons or controls to supply constant fan speeds. However, you can tinker with the motor’s wirings to change the fan’s constant RPM.

Start this project by using a multimeter set on resistance to find the correct wire to use. Also, ensure that you set the measurements to ohms.

Then, attach the red probe to the white or common wire. Poke the ends of the other wires and check the readings. Take note of those measurements to identify which wire you need to attach to change the fan speed.

As you’re looking at the measurements, remember that the lower the resistance reading, the faster the fan speed. Attach your ideal wire to the furnace based on your heating needs or preferences. Once you have your chosen wire, follow the next steps:

  1. Connect the white or common wire to the neutral port on the furnace’s control board.
  2. Choose your chosen wire to give the space adequate heating to the terminal labeled ‘heat.’
  3. Attach another one of your preferred wires to the port labeled ‘cool’ or ‘cooling.’ Take note that the wire attached to this terminal is going to be for supplying cold air from the furnace.

Always bear in mind that you shouldn’t switch the heating and cooling wires. Doing so might put the heating unit at risk of contracting permanent damage.

Check out this digital multimeter kit on Amazon.

ECM Blower Motor Adjustments

The procedure for adjusting the blower motor on an electronically commutated motor (ECM) is similar to the steps to change the fan speed on a PSC furnace. You might not even need a multimeter for this operation. But you should have the owner’s manual nearby to know the resistance measurement of each wire.

Usually, you will see each wire's programming on a label or sticker at the bottom or side of the blower motor. Aside from the green (common) and black and white (high-voltage) wires, the four wires generally attached to the motor are the speed wires. Connecting these speed wires to their appropriate terminals allows you to change the furnace’s fan speed.

Once you know each wire’s speed readings, connect them to the proper ports on the blower motor. Take note of the label on each port and make sure that they coincide with your desired programming.

For example, your furnace’s ECM motor might have ‘5’ as the coldest setting and ‘1’ as the warmest option. So, you can connect your preferred highest fan speed in the port labeled ‘5’ and your chosen slowest fan speed in ‘1.’

You can also watch the video below to gain more insight on how to adjust the furnace fan speeds using PSC and ECM motors. This clip also shows the steps to change the blower speed for variable speed furnace motors.

Additionally, the procedure to adjust the blower speed may also depend on specific models made by certain manufacturers. For example, read our post on how to adjust the blower speed on a Goodman furnace to see the steps for this task.

What Speed Should Furnace Fan Run?

Most furnace fans should be fine when moving at 1,200 RPMs. Certain high-powered models can sustain blower speeds of up to 1,500 RPM.

Can I Upgrade My Furnace Blower To Variable Speed?

Inside of a furnace showing the motor

Some furnace models may accommodate different fan motors, allowing owners to upgrade their standard PSC or ECM models to variable-speed variants. Doing so can supply households with different benefits like:

  • Quiet operation: Variable-speed motors are often silent, unlike single-speed motors, such as PSC units.
  • Energy savings: Some variable-speed motors adjust fan speeds automatically. For example, the furnace’s fan may start at 2/3-speed before increasing RPMs after 10 minutes of operation.
  • Reliable performance: The quick fan adjustment features allow variable-speed motors to cause less strain on their internal components, enhancing their serviceable life.

Check out this variable-speed blower motor for gas furnaces on Amazon.

Can A Furnace Run Without A Blower?

Most gas furnaces need to have their blowers running to generate sufficient cooling or heating to connected spaces. If the furnace’s fan isn’t turning, the heat becomes trapped inside the system. This event can lead to serious or irreparable harm to the heating unit.

On the other hand, electronic ignition systems usually don’t have blower motors. It’s because these models typically don’t have pilot lights and use electricity to provide comfortable temperatures in homes.

How Much Does It Cost To Replace A Furnace Blower?

A boiler and a home furnace in the basement

Replacing a furnace blower usually costs $400 to over $600 on average. The overhead typically includes professional labor, along with parts repairs and replacements.

It’s also often cheaper to have a single-speed blower motor replaced than changing a variable-speed model. Accessibility and the motor’s manufacturer can also affect prices in replacing furnace blowers.

Check out this OEM replacement furnace blower on Amazon.

Is It OK To Run Furnace Fan All The Time?

Running a furnace fan continuously can lead to higher utility costs than average. A typical electric furnace will generally produce $0.13 per kilowatt-hour. On the other hand, gas furnaces require fewer expenses since these models typically cost 63% less to function than their electric counterparts.

With those numbers, an electric furnace fan running for a year would demand about $2,600. But a gas furnace should only require approximately $1,800 per year in utility costs.

It’s also not OK to run a furnace fan endlessly, particularly in inclement weather. Homeowners should turn off their heating units in the summer to reduce indoor warmth.

Final Words

Technician doing a system diagnose in the furnace system

Adjusting a furnace fan speed typically requires rearranging some wires on the heating system’s control board. Careful attention to detail is a necessity to achieve the right fan speed and avoid serious mishaps. Incorrectly inserting a wire may also lead to irreparable damage to the heating system.

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