In the HVAC world, we love to sing the praises of variable-speed equipment. Compared to standard, single-stage air conditioners, variable speed units provide better, more consistent comfort and improved humidity control.

But wait. Are we talking about variable-speed blowers, too? Is a variable speed AC the same thing as a variable speed blower?

There’s a lot of confusion around this issue, so let’s clear it up right here and now. A variable-speed blower is different from a variable-speed AC compressor. When we say things like “variable speed air conditioner” or “variable speed HVAC system,” we’re usually referring to the air conditioner’s compressor.

Ok. So, what is a variable speed blower, anyway?

Great question. Your HVAC system’s blower is its indoor unit. You may also know it as your furnace fan or air handler.

Regardless of what you call it, we’re talking about the same piece of equipment. The part that actually, you know, blows air is the big fan that sends air through your ducts. In a standard AC system, the blower just runs at one very high speed whenever the system calls for cooling.

However, when you have a variable speed blower, the fan inside the indoor unit speeds up or slows down to more accurately match your cooling needs. It’s also possible to pair a variable-speed blower with different types of air conditioners.

For example, you can have a variable-speed blower with a single-stage air conditioner. While the air conditioner’s compressor can only cool at full capacity, the variable speed blower will move air through your ducts at different speeds depending on the cooling load.

Then why would you want a variable-speed compressor?

Because it further refines the AC’s ability to provide exactly the right amount of cooling. A variable-speed blower is great no matter what kind of compressor you have. But a variable speed blower paired with a variable speed compressor? Well, that’s even better! Way better.

Variable-speed compressors always pair with variable-speed blowers. Together, these two components give you:

  • The most perfect possible amount of cooling to maintain your thermostat setting
  • Excellent humidity control: since the system runs at a low speed most of the time, it continuously removes humidity from the air.
  • Superior operating efficiency since the compressor isn’t turning on and off all the time or only running at full capacity
  • Quiet operation from the blower fan (it’s moving air at a slow speed, after all) and from the outdoor unit

Do you get some of these benefits with, say… a variable speed blower paired with a single-stage AC? Sure. You get a little improvement. But a variable speed compressor is what can help you maximize the value of your variable speed blower.

Here’s a quick cheat sheet for variable speed

Refer back to this if you’re ever confused about variable speed compressors vs variable speed blowers:

  • Variable speed blower = indoor unit
  • Variable speed compressor = outdoor unit
  • Variable speed blowers deliver maximum comfort and efficiency when paired with a variable speed compressor.
  • You can pair a variable speed blower with a single-stage or two-stage AC compressor and enjoy a modest boost in comfort and efficiency.

What about furnaces?

Many high-efficiency furnaces have what’s called a modulating gas valve. Instead of just providing one level of heat (the highest level possible), the furnace gives your home the right amount of heat to match your needs at any given moment.

It’s kind of like having a variable-speed compressor for your AC, except it’s for your furnace.

Anyway, a furnace with a modulating gas valve also always pairs with a variable-speed blower. This distinction is less confusing because, unlike with ACs, we don’t use the same terminology (variable speed) to describe the heating capacity and the blower capacity.

And yes, you can pair a variable speed blower with a two-stage or modulating gas valve. The AC analogy mostly holds although you can’t pair a variable speed blower with a single-stage gas valve.

Oh, yeah. There’s this one exception to all of the above…

It’s a new product (as of June 2020) and everyone in the industry is still learning about it. Bosch now makes a heat pump with a variable-speed compressor that pairs with a single-stage furnace.

This heat pump is a low-priced unit that’s intended to match up with a wide array of existing furnaces. Bosch is trying to make it so that you can keep your furnace and still get a variable-speed air conditioner for improved efficiency during the cooling season.

Does it perform? We have no idea. Not yet anyway.

It’s important to keep in mind that this is a very atypical heat pump. We just figured we’d mention it because, hey, it’s out there! The more important thing to remember is that 99.9% of the time, a variable-speed compressor will only pair with a variable-speed blower.

When it comes to air conditioning, the words “variable speed” is always good.

Yep, variable speed anything is an upgrade for comfort and energy efficiency. If you live in Metro Atlanta and are thinking about a new, more efficient AC for your home, give us a shout!

Our team will listen closely to your concerns and analyze your existing system. We’ll also help you select the right HVAC equipment, whether it’s variable speed or not.

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