The average homeowner doesn’t often ask – how many watts does a furnace use?
But those of us who are conscious about energy use want all the data we can get to make HVAC equipment decisions for our home and business.
There are variables discussed below that will assist you in narrowing the estimate of how much energy your furnace uses.
How Many Watts Does a Furnace Use?
In general, your furnace’s blower is running on anywhere from 60 to 900 watts with an average of less than 200 for ECM motors and around 550-700 for older-style PSC motors.
This is a general chart based on the most common blower types.
Furnace Blower Watts Table
|PSC Single Speed Blower Furnace||500 – 900 watts|
|PSC Blower/ X13 Blower (Multi Speed) Furnace||450 – 800 watts|
|Variable Motor (ECM Motor) with Modulating/Two-Stage Furnace||90-200 watts, but can use up to 600 watts+|
|Variable Motor (ECM Motor) with Single Stage Furnace||250-300 watts|
Note: The furnace size is based on 80,000 BTUs. The estimation is based on no excessive static pressure AND the fan switch is in the “ON” position during the heating season for even distribution of heat.
The Challenge of Answering How Many Watts Does a Furnace Use?
There are many variables, some of which are discussed in the next section, that determine how much power a furnace uses. Most of the energy is used by the blower, of course – more than 90% of the electricity.
A small percentage of electricity is used to power the control board, capacitor, switches and other internal electrical parts.
There is very little consensus among HVAC technicians about how much power a furnace uses to circulate air through your system’s ductwork. Debates rage on HVAC pro sites like HVAC-Talk and others. This is because of the many factors affecting energy use.
The only definitive way to know how many watts a furnace uses is to use a wattmeter and run the blower at each of its speeds to see how many watts it is consuming.
Factors Affecting How Many Watts a Furnace Uses
Here are the variables that answer the question – how many watts does a furnace use? Each includes details about how it affects furnace watts.
Type of Motor
There are two common blower motor types, PSC and ECM, and which type your furnace uses is the most significant factor in wattage. This difference is shown in the Furnace Blower Watts Table above.
PSC motors, or permanent split capacitor motors, use 550-800 watts of energy on average. They are an older style of motor that has served the HVAC equipment industry and homeowners very well for decades. They cost less, but use more energy and can’t provide quite the same level of indoor climate control. There are single-speed and multiple-speed PSC motors. If your furnace is more than 10 years old, it likely has a PSC motor. Efficiency of PSC motors is 40-60%.
ECM motors, or electronically commutated motors, use between 90 and 300 watts; a few use less when running on the lowest speed – as few as 60 watts. ECM motors are variable-speed motors, speeding up and down in small increments like cruise control to match the performance needed from your furnace or air handler. If your furnace is newer, there’s a good chance it uses an ECM blower. ECM motors are more than 80% efficient in their use of electricity. They are more complex and cost more to replace, but their reliability is superior to PSC motors and are designed to run all the time if necessary.
Did you know? As of 2019, the US Department of Energy has mandated that new residential furnaces and air handlers use ECM motors.
Check this out! Here’s a video on ECM vs PSC Energy Use that you might find informative and interesting. It tends to throw something of a wrench in the conventional wisdom. However, because ECM motors run at much lower speeds than PSC motors, they are still a more energy efficient choice. Keep in mind that this is one ECM motor – there are many, and our pro opinion is that most ECM motors are more efficient than the one shown when operating on higher speeds. We believe our Table above to be accurate for most ECM blowers.
Tell us what you think! We’re always open to input from readers, especially those with experience on the issue. Many HVAC pros read Pick HVAC, so feel free to join the conversation!
Size of the Motor
For either type of motor, the larger the motor it is, the more energy it will use. Most blower motor series range from about 1/3 to 1.0 horsepower. Even the largest ECM motor uses less energy than a small PSC blower motor.
Generally speaking, the larger the furnace or air handler, the larger the motor. But ductwork size and distance play roles too.
Many PSC motors and all ECM motors can operate at a range of speeds.
You’d notice perhaps a 50% to 500% variance for any given blower motor in energy use in watts at its lowest speed and highest speed. The range is potentially greater on an ECM motor; PSC motors vary only slightly in energy use between the lowest and highest speeds.
When ducts are properly sized, air pressure within them is appropriate for the HVAC equipment. Air flows freely through them without needing excessive force.
When pressure is too great – think trying to blow hard through a small-diameter straw – your blower motor will have issues.
PSC motors will work harder and potentially burn out. They can’t moderate their speed; Low speed is low speed. High speed is high speed, for example.
ECM motors will work harder and use more energy. One of the advantages of an ECM motor is that if your system needs 1200 CFM (cubic feet/minute) of airflow when running at full capacity, the motor will deliver it. If the ductwork is properly sized, the motor will use much less energy than if the ductwork is too small and the motor has to use more energy to maintain 1200 CFM air flow.
This is just one reason why properly sized ductwork is a critical part of a healthy, reliable and energy efficient heating and air conditioning system. See our Ductwork Sizing Calculator with a lot more information about the importance of ductwork to efficiency and indoor comfort.
Setting on the ECM Motor
ECM motors can be programmed to run at a specific speed or range of speeds and voltages.
This gives the HVAC technician the opportunity to fine-tune the motor to move exactly the right amount of air through the system to optimize indoor temperature and humidity control.
As a result, the ECM motor will use more or less energy based on the settings.
Length of Cycles – with Factors
It’s no surprise that the longer a motor runs, the more energy it will use regardless of it being an ECM or PSC motor.
Cycles should last 8-15 minutes. Their lengths vary based on the outside temperature vs indoor temperature, thermostat setting, your home’s insulation level and whether the system is in Heat mode or Cool mode.
2-4 cycles per hour is normal. In the coldest part of winter and hottest stretch of summer, expect your system to run a bit more often and/or for longer cycles.
All of this means the blower is running up to 35 or 40 minutes per hour.
What’s the Bottom Line
Despite the occasional ECM energy-hogging motor, it is pretty clear that ECM blowers run much more efficiently than PSC motors – using 50% to 75% less energy.
A summary of the averages shows:
PSC motors use 500 to 900 watts
ECM motors use 90 to 300 watts, but if the ECM motor isn’t functioning properly, it can use as much as 600 watts, possibly even more.
If you have an ECM motor, and your electric bills are higher than you expect, have a certified HVAC technician check the motor for proper operation.
But also keep in mind that regardless, the motor is not the main factor in how much energy your heating and air conditioning system uses.
Instead, the biggest potential waste of energy – or energy savings – is in the efficiency of the equipment you have. Our Cost to Run a Gas Furnace Calculator and guide shows the importance of AFUE/energy efficiency in a furnace. Check it out, and change efficiency ratings to see how much you can save with a high-efficiency furnace. This page allows you to directly compare operating costs between furnaces of different efficiencies.
The next time you need a new gas furnace or heat pump air handler, choose an Energy Star certified unit with proven energy-cutting efficiency levels.