Few products are pushed harder in the heating and air conditioning 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.
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 exactly what a variable speed furnace is.
What is a Variable Speed Furnace?
The term variable speed furnace is used to describe furnaces that have a more energy efficient variable speed blower motor. These blower motors move cooled air (in summer) and heated air (in winter) through the ductwork in your home.
A conventional single speed furnace without variable speed technology uses a simple motor with multiple speed settings that must be manually adjusted. These different speeds are used by a contractor to adjust airflow to the proper amount.
A variable speed furnace, unlike the single speed furnace, will self-adjust its fan speed. It will make these speed adjustments based on sensor readings.
There are multiple models of variable speed furnaces including two stage and modulating variable speed furnaces. But modulating furnaces won't be covered in this article because most home owners tend to be deciding between single and variable speed.
These gas furnaces claim to have three major benefits.
- Saves Money
- More Comfortable
Let's look at each of these claims one at a time.
Do Variable Speed Furnaces Save Money?
On paper the answer to that question is yes. In reality, it will cost you more in the long run.
Because variable speed gas furnaces have a more efficient motor, on average home owners save about $40 a year in electricity with a variable speed unit. Far below what manufacturers claim.
Manufacturer claimed savings are based on a motor in constant operation. 24 hours a day 365 days a year. In this case, variable speed dc 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 a variable speed blower's ability to save energy. 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 increase energy consumption. 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 $750-$1500.
You can expect to need either or both of these replacements every 7-10 years. As you can see, any energy efficiency gain and savings on your electric bill 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, properly set up furnace compared to the clunker in your home now.
Quieter than a new properly sized furnace with a standard motor? No. A furnaces variable speed ability will have no effect on noise.
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 air flow, poor duct design and oversized equipment.
Just because the variable speed furnace slowly ramps up to speed over 5 seconds rather than the 2 seconds from a single speed furnace, doesn't ensure quieter operation.
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 will be quiet.
The most important aspect of a heating and cooling system is the air flow. It's ALL about air flow.
No matter what style motor, just the right 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 requires 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?
A variable speed system also claims that with this advanced technology you'll be better able to precisely control air distribution and remove hot and cold spots.
Comfort is a funny thing. Every person describes it differently. The desired temperature in a home varies. 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 manufacturers are misleading home owners with the claim of better comfort.
I've installed variable speed furnaces in my own home and for my 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.
Can It Improve Indoor Air Quality In Your Home?
Yes it can but not on its own. This is one of the few areas where these furnaces have a positive impact. Indoor air quality is dependent on air flow and ventilation.
A variable speed motor can help clean the air in your home. These motors can work well in constant operation. Whether it’s in heating or air conditioning mode, the motor will continue to slowly circulate air, allowing your air filters to capture more contaminants.
But for any significant change in indoor air quality you need to run your blower 24 hours a day and you have to add the added indoor air quality accessories that will be providing the benefit.
Is the Fancy 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 quality contractor install your single speed 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 to last 20 trouble-free years in your home. You’ll most likely be replacing this system or making very large repairs in the 10-15 year range.
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 trying 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, you lose.
Remember the key point earlier? You will be happy with any heating and cooling system in your home as long as it's installed by a quality heating and air conditioning 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 when replacing your gas furnace and air conditioner.