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Revised:
November 22nd, 2021
When it comes to considering your next HVAC purchase, there are a bunch of options for you to choose from these days. Nowhere is this more true than in the various motor blower speeds available for your air conditioner and furnace.
At Fire & Ice, we specialize in educating you on all your options so that you can make the best choice for your budget and comfort needs. We’ve sat down with thousands of homeowners who don’t know the differences in technology between one system and the next. It can all seem pretty confusing unless it’s explained by an expert.
Many are surprised to learn of the benefits that a variable-speed air conditioner or furnace can have compared to their current single-speed system, even if those options aren’t the right choice for them.
In this article, we’re going to break things down for you as if we were having a face-to-face discussion in your home. The goal, as it is when we visit all prospective customers, is to give you all the facts that you’ll need to make the right decision for you and your home. By the end, you’ll be better informed about your choices and be able to ask the right questions to HVAC salespeople.
How Furnace Single-Speed Fans Work
Motor blowers come in three major varieties, single-speed (or single-stage), two-speed (or two-stage), and variable speed (or modulating).
For years and years, fans ran at single-speed. It was either off or on at 100%. The first forced-air furnaces ran that way, and you can still buy furnaces with the same technology. When it kicks on, you can hear it in almost any room of your house, and you’ll feel the rush of hot air warming the space.
And when it shuts off, the hot air dissipates - probably faster than you’d prefer. The advantages of this are that the technology didn’t change much. It was tried-and-true. They run off of a permanent split capacitor (PSC) motor. PSC motors go from 0 to 100% almost instantly. They are:
- Cheap
- Noisy
- Inefficient
- Unreliable
- Hard on HVAC equipment. The constant starting and stopping wear out the mechanics quickly.
- Not manufactured anymore. They’re obsolete.
Electronically commutated (EC) motors are taking the place of PSC motors. They have paved the way for variable-speed blower motors. They are:
- More expensive
- Quieter
- Efficient
- More reliable
- Easy on HVAC equipment. Since they rarely run at 100%, it’s easier on the parts.
Variable-Speed Motors Create Total Comfort
Picture a bottle of your favorite vinegar and oil salad dressing. The oil and vinegar are two halves of a whole until you shake it up. When you shake it, they become one.
That’s what’s happening when your furnace kicks on. Hot air is mixed with the cold. So far so good.
But when you stop shaking the bottle of dressing, what happens? The ingredients separate again. Ditto the indoor air when the furnace turns off. It doesn’t take long for the cold air to sink to the bottom, while the hot air goes to the ceiling. And hot air leaves the upstairs faster than downstairs because it can escape through the ceiling into the attic, crawlspace, or outdoors.
This is what we mean when we talk about hot and cold spots in your home. In some rooms, the air is comfortable. In others, the air hasn’t had the chance to mix well. It’s cool in the winter, warm in the summer. The upstairs and downstairs are at different temperatures.
Now picture the salad dressing being shaken continuously and slowly. It stays mixed. Even though you’re not putting a lot of energy into shaking the bottle, the results are a fully mixed concoction.
That’s what a variable-speed fan does to your home. The air handler is running at a low level once the optimal temperature is reached. The air stays mixed. The warm and cool stay mixed. Your optimal comfort stays constant; it doesn’t vary if the furnace or air conditioner is running, even if it’s at a slow speed.
A variable-speed motor starts at a slower rate than a single-speed one. It’s a soft start. It’s like easing down on the gas pedal, not flooring it. It takes approximately 45 seconds to get to full speed.
Other Advantages to a Furnace’s Variable-Speed Motor
- It’s energy-efficient. Even though a variable-speed fan air handler is constantly running, it is usually doing it at a low level. This saves energy because your system doesn’t have to turn on and off often, and it spends much less time running at the highest level. A variable-speed system can adjust accordingly to use only the power needed to maintain a consistent temperature in your home.
- It’s quieter. A furnace is at its loudest when it’s turning on and off and when it’s running at high speeds. You always know when the furnace starts. A variable-speed model avoids this by running at 100% only when it needs to. It starts slowly, as well, which reduces its sound.
- It produces better air quality. Because the fan runs longer, the air is being filtered constantly, which removes impurities. And if you have a whole-house humidifier or dehumidifier ducted to your HVAC, they have more time to condition the air. That leads to a perfect and stable humidity level.
- You get better comfort control. The fan speeds of a variable-speed furnace keep the temperature and humidity even all the time. Instead of being hit with bursts of hot or cold air, conditioned air is delivered consistently. It can keep up with your thermostat’s setting to within a half degree.
- A variable-speed fan is perfect for zoning. It’s easier to deliver the correct amount of conditioned air to each zone in your home. You get fewer hot and cold spots.
- Reliability: The heat exchanger doesn’t go hot-cold, hot-cold, so it doesn’t expand and contract as much. Consider a metal spoon. It will break if it’s bent back and forth repeatedly. The same principle applies to your heat exchanger. Every time a single-stage piece of equipment starts, the metal inside will expand quickly. And when the unit shuts off, the metal contracts quickly. Heat exchangers don’t have lifetime replacement guarantees because the manufacturers know that part will wear out.
For example, the technology behind Trane’s Comfort-R is the ramping system of the ECM variable-speed motor. During cooling, the ECM motor ramps up slowly, moving air across the coil and giving it a chance to cool. The motor then ramps up to 80%, where it stays for 7.5 minutes. By ramping up gradually and running longer at a lower speed, the variable speed system is able to remove more moisture from indoor air. After the thermostat is satisfied, the motor then ramps down to 50%, where it operates for three additional minutes.
While it’s at its slower speeds, it moves less air than a one-speed fan, therefore it must have a longer run cycle to move the same amount of air.
It’s at this point customers ask a logical question: If a variable-speed fan runs longer than a single-speed, won’t it cost more to run the former?
The answer is no.
It takes less energy to run at 60% than 100%. While a single-stage has to ramp up to 100% every time, the variable-speed can cruise at 60%, keeping the temperature steady. The unit doesn’t start and stop all of the time, which takes the most energy.
Drawbacks of a Variable-Speed System
The primary downside is the initial cost. The systems don’t come cheap, even if they largely make up that cost in the long run.
Another downside is repairs. If a part breaks, it can be costly regardless of the system. But the advanced technology inside a variable-speed air conditioner can often incur increased replacement costs and labor costs. Even if a system is under warranty, most don’t cover labor costs, so you can still be on the hook for more than expected depending on the repair.
The last drawback is that for variable-speed equipment to function correctly, it has to rate, or match. Your furnace (or air handler) blows both heat and cool throughout your ducts. If you have a variable-speed air conditioner, it must be paired with a variable-speed furnace. Otherwise, one unit will operate at hundreds of speeds, but the air from it will be circulated at only one if your existing furnace is a single-speed.
In addition to that complication, unless equipment rates, the warranty often won’t cover the units. If they don’t rate and one fails, you’re stuck with a huge bill.
Take the Next Step in Columbus, Ohio
The reasons we upgrade our phones or computers are technological improvements. You’ll find very few people who go from an iPhone 11 to a 6. We want more features, more bells and whistles. And Apple knows it; that’s why they’re continuously improving their products.
Customers don’t want the new and improved furnace; They want the benefit of the unit.
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As we’ve discussed, variable-speed offers a host of benefits over a single-stage HVAC. But we’re aware that it’s not a fit for everybody. If you’re replacing a unit and planning to move in the near future, making the investment in a higher-priced furnace may not sound logical.
- How long do you expect to stay in the home? If it’s less than 5 years, you won’t see a lot of the long-term cost savings from a variable-speed system. But if you’re planning on raising a family in this house, for example, a more efficient system might make more sense.
- In this case, size can make a difference. Modern systems are more efficient than older systems, but they’re also larger as a result. And variable-speed units are the largest of the bunch. Make sure the area where you’re planning on housing your outdoor air conditioning unit is indeed big enough for the dimensions of the equipment. This can apply to height as well, if you don’t want a unit peeking over a window sill.
Ditto if you’re happy with the specs of your current system and are comfortable in your home already. If your single-speed is doing the job adequately, then a replacement single-stage furnace/AC is good enough.
READ MORE ABOUT HVAC SYSTEMS:
A Guide to High-Efficiency Furnaces
Single-Stage, Two-Stage and Variable-Speed Furnaces: Differences and Benefits
If you’re in Columbus, Ohio, or the surrounding area and are ready to figure out which is the best fit for you, click below to schedule your free in-home estimate.
