Are There Benefits to a Variable Speed Furnace?

 July 1, 2015

By  Robert Bradford

No product is pushed harder in the heating industry than variable speed furnaces. There are three reasons for this:

  • Rebates to consumers are closely connected to them.
  • Contractor pricing and bonuses are based on how well they sell these furnaces.
  • They’re high profit for manufacturers.

Because of this, it’s difficult to find anything but marketing hype about these furnaces. Most of it is not only misleading but wrong. That’s not surprising.

But using independent studies and years of consumer experience we can find the true pros and cons of these furnaces.


Let’s first make sure we understand what exactly is a variable speed furnace.

What is a Variable Speed Furnace?

The term variable speed furnace is used to describe furnaces that have a variable speed blower motor. These blower motors are the motors that move air through the ductwork in your home.

Furnaces without variable speed technology use a simple motor with multiple speed settings. These speeds are used by a contractor to adjust airflow to the proper amount.

The difference on a variable speed motor is that it will self-adjust its speed. It will make speed adjustments based on sensor readings within the furnace.

Variable speed furnaces claim to have three major benefits.

  • Saves Money
  • Quieter
  • More Comfortable

Let’s look at each of these claims one at a time.

Does a Variable Speed Furnace Save Money?

On paper the answer to that question is yes. In reality, it will cost you more in the long run.

On average, homeowners save about $40 a year in electricity with a variable speed furnace. Far below what manufacturers claim.


Manufacturer claimed savings are based on a motor running 24 hours a day 365 days a year. In this case, variable speed motors do consume less electricity then a standard motor.

The problem is few people have a good reason to run their blower motor that way.


The claim of saving money is based solely on electrical usage. A high efficient variable speed furnace and a high efficient standard motor furnace will use the same amount of fuel. (Natural Gas, Oil, Propane)

Another problem with these claims is that they're based on properly sized ductwork. One of the most common problems in homes today is the installation and design of the ductwork system.

A variable speed motor will try to compensate for this failing. As it does it will run harder and consume more electricity. This is a band-aid fix to a major problem.

Trying to fix poor ducts by using a different motor is like trying to fix bad wiring in your home by changing how much power the electrical company is providing.

The only solution for a poor duct system is to have a good contractor repair it.

But here’s the biggest problem with the claim of money savings.

Any savings from less electrical consumption is out the window once the equipment needs its first repair.

In a variable speed furnace both the motor and the control module are far more complicated. This makes them more repair prone. The cost to repair either of these items normally is anywhere from $500-$1000.

Variable Speed Furnace Parts

Parts for a Variable Speed Furnace. They look expensive because they are expensive.

You can expect to need either or both of these replacements every 7-10 years. As you can see, any savings of electricity is quickly wasted with the cost of repairs.

Silence of the Motor

Is a variable speed furnace quieter? Quieter then what? Quieter than your old furnace? Most likely. But so is any new furnace compared to the clunker you are replacing.

Quieter then a new properly sized furnace with a standard motor? No.

You'll notice that manufacturers are vague when it comes to the amount of sound a furnace makes. There are no decibel ratings of furnaces like there are for air conditioners. Not even for comparison.

That’s because the noise that people most often complain about is not caused by the motor. It’s from improper airflow, poor duct design and oversized equipment.

So any properly sized furnace installed with proper duct design by a good contractor will be quiet.

And that’s the key so I’ll say it again. Any properly sized furnace installed with proper duct design by a good contractor.

Here’s why:

The most important aspect of heating and air conditioning is the airflow. It’s ALL about airflow.

No matter what style motor, the required amount of air needed for the furnace to operate properly will be the same.

As a technical example, if you have a 3 Ton air conditioner your air handler/furnace will need to move 1200 CFM of air.

(CFM stands for cubic feet per minute and is used as a measurement for air movement. 400 CFM per ton is a general rule of thumb. 3 Tons x 400 CFM = 1200 CFM)

That amount of air will make the same amount of noise no matter what motor is pushing it.

Will You Be More Comfortable?

Comfort is a funny thing. Every person describes it differently. This makes it easy to put a marketing spin on it since it’s hard to define.

It also makes it hard to prove the manufactures are misleading homeowners with the claim of better comfort.

Except this:

I’ve installed variable speed furnaces in my own home and for family for testing.

In every case, there was no comfort difference between the new furnace and the standard furnace that was removed.

My experience is backed up by every study I have found.

A perfect example is from a study by the U. S. Department of Energy in January 2014. Standard motors were removed and variable speed motors were installed to measure the differences.

Here is a quote from the conclusion of that study regarding comfort:

3.5 Homeowner Feedback: Before monitoring began and at the completion of long-term monitoring, home residents were interviewed to assess their satisfaction with the HVAC system. In general, the responses have been mildly positive. There were a few comments about different sounds, and people noticed little if any changes in comfort.

Nothing beats real people talking about their experiences to shine a light on marketing hype.

Is a Variable Speed Furnace Worth It?

If you’re looking to enjoy the claimed benefits the answer to the above question is no.

You can enjoy these benefits without the disadvantages of variable speed furnaces. Just make sure you have a good contractor install your furnace and duct system.

It’s not that they’re bad furnaces. And I won’t say that there is never a reason to install them. There are times when they might be a better fit.

Just keep in mind these furnaces are not built for your benefit. They’re built for the benefit of the manufacturers.

Furnace manufacturers, like all companies, attempt to improve profits. I don’t have a problem with that. I do have a problem with it when they do it by deceiving the consumer.

In this case they are tying to do it by having higher equipment turnover. By adding repair prone features, they sell more equipment and parts all while telling you it’s for your benefit.

Replace the furnace or pay for high mark up parts. Either way manufacturers and unethical contractors win.

Bottom Line

Remember the key point earlier? You will be happy with any furnace as long as it's installed by a good contractor. And a good contractor will rarely recommend a variable speed furnace.

So that leaves you with one job. Don’t focus on equipment options. Focus on choosing the right contractor. Nothing is more important.

If you want more information on finding good contractors click here.

Robert Bradford

I'm Robert Bradford. I've been in the heating and air conditioning industry for 30 years. Ov​​​​​er 40 if you count the years I helped my father as a kid. On this site, I share everything I've learned about finding the best HVAC contractors and equipment for your home. I'm happy to say that over the last few years, The Comfort Academy has grown into a trusted site with thousands of informed site visitors each year.

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  1. You should also mention the misleading claims that VS motors provide “cleaner” air and also that they run continuously to do that (with no mention of having to place the fan switch to the ON position to accomplish this). Also, they claim that VS motors continually monitor your home’s heating and cooling needs and will slow down as the temp approaches the set point (??????). I’ve never seen any sensors installed on any brand that will do that, unless a communicating system thermostat monitors that, but I’m doubtful. I’ve always wondered how a VS motor monitors anything. Seems like motor current is the only factor, and perhaps internal temp sensors built into the motor controller.
    As an HVAC contractor, I always shy away from selling VS furnaces for the costly maintenance “down the road” reason. Whether under warranty or not, it will definitely eliminate any savings racked up by then.

  2. What an excellent and honest article! I have been researching the options provided to me by the contractor and was trying to find information on whether a VS furnace was worth the money. You’ve just saved me a lot of money and potentially more money down the road. Thank you!

  3. Seems like these types of blowers are ideal for a zoned system. My house is a 2 storey house that needs air sometimes upstairs and sometimes downstairs… so if I had a single speed motor… and half of my ducts were closed… I now have 2x as much air going through them… but with the multi speed fan, that air is reduced and that “noise” is lessened.

  4. Hi Robert this is Carlos. Just purchased a 3-1/2 ton system to replaced the old dog. We had for over 15 years, the unit was working fine. But , I was talked into getting a 16seer system. So far both heat and cool are fine. Except the Gas Furnace is extremely loud. It sits on the hallway facing our living room. This is a 2 stage furnace with a variable speed motor. In your infinite wisdom, is there a way to slow the the motor so it won’t be as loud.
    Thanks !

    1. Hi Carlos. The short answer is, yes, there are speed settings on a variable speed motor.

      And here’s the long answer…the speeds should be set by your installing contractor. Airflow settings are a HUGE part of the proper operation and efficiency of your system. A good contractor will take the time to set up a new system and leave documentation proving its operation. In your case, proving it’s operating as a 16 SEER system.

      It could be a matter of just slowing down the motor but the noise could point to other issues. The system could be oversized or the ductwork may be undersized. It could also be how it was installed. No matter what, you should contact the installing contractor. If they won’t perform the set up it’s time to find a better HVAC contractor.

  5. We have a unit that is possibly going bad, so I’m researching new units. We live about an hour or so north of Houston, Texas, so we are very hot and humid most of the year, and pretty chilly in the winter. We are some of the few people who run our ac or heat almost every day of the year. This is an older home, but we spray foam insulated the attic and replaced all of the windows.

    That being said, what type of unit would be best, if not a variable speed? We’d like to keep our cooling Costs down, and the unit needs to cool just over 3,000 sq ft. I really liked the idea of a VS…until I read your article!

  6. Thanks for this candid assessment of the differences between these two motor types, Robert. You just saved me $700!
    Will be installing a new electric furnace in my Montreal house — yes, electric, as Hydro Quebec’s domestic rate is only six cents per kilowatt hour (and drops to 4 cents/KwH whenever the temperature is above -13 C if one uses bi-energy heating).

  7. Thank you for all the information you provide! Very helpful!

    You say: "And I won’t say that there is never a reason to install them. There are times when they might be a better fit."

    Could you provide an example or two of when a variable speed might be a better fit? In my house, the bottom level of the house gets warmer quicker in winter and cooler quicker in the summer than the main floor which then causes us to adjust the the thermostat setting to not make anyone sweat or shiver unnecessarily. Is VS a fit for this situation?

    1. Good question. The long answer will be discussed in an upcoming article. The short answer is while they have their disadvantages compared to the tried and true PSC motors we’ve used for years, I recommend multi-speed ECM motors over variable speed. ECM motors are here to stay and more than likely will replace all PSC motors in the near future.

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