Monday, March 26, 2007

Variable Speed Air Handlers vs. Single Speed Air Handlers

Did you know that, if you have a central air conditioning system, that it is usually a split system. This means you have indoor equipment and outdoor equipment that make up the entire system. The indoor equipment is called the air handler. So when you are making a decision about your HVAC system and the question of a variable speed air handler versus a single speed air handler comes up, what is the best choice? Well, I’m glad you thought to ask.

Let me explain what “variable speed” means in reference to your air handler. Lennox Home Comfort Systems describes it this way, “‘Variable speed’ refers to the fan motor inside the air handler—the indoor part of an air conditioner that moves cooled or heated air throughout the ductwork of your home. An air handler is usually a furnace or a blower coil. Unlike conventional single-speed motors, a variable speed motor runs at a wide range of speeds to precisely control heated and cooled air throughout the home.”

There are several advantages to using a variable speed air handler.
1. Variable speed motors cost less to operate because they usually run in low speed, unlike single speed systems which run in “high” 100% of the time.

2. Because variable speed air handlers gradually work their way from low speed to high speed, there is no blast of air from the vents.The transition when the machine turns on is very mild and it can be difficult to even tell when the machine actually turned on.

3. The noise level is much lower for variable speed air handlers because they usually run in low speed.

4. Variable speed air handlers make it much easier to create different zones in your home so that you can heat or cool one room differently than another room.

5. Variable speed air handlers do a much better job of removing humidity from the home, making you more comfortable in your home. Some systems can remove as much as 24 gallons per day from a home!


More comfortable, more efficient, and less noisy….sounds like a winner to me. Variable speed air handlers always trump single speed ones. Just make sure that your indoor and outdoor equipment are correctly matched by your HVAC sub. This will help your machine to run at its highest potential efficiency.

6 comments:

John Vollman said...

Paul,
I listen in every weekend as I remodel my shotgun camel back. Following most of your suggestions: got my 6mil poly down, going to foam the entire place (if the budget holds!), got to replace the HVAC, going with an American Standard variable speed heat pump. Manual J says 2 tons. Question is: wouldn't it be better to save $$ on the variable speed and instead do a whole house dehumidifier (Aprilaire 1720) rather han try to get an AC to do dehumidifying? Or should I just suck it up and do both?
Thanks!

John V.

Paul LaGrange said...

John, thanks for posting your question. There are advantages to both methods of using the variable speed air-handler in conjunction with the dehumidifier or using a standard air-handler with the dehumidifier. When using a variable speed air-handler it not only removes a greater volume of moisture from the air when compared to a standard unit, but is quieter, energy efficient, and usually makes up for some inefficiencies in ductwork.

The benefit of the dehumidifier is its ability to maintain a favorable indoor relative humidity range of 40 -60% no matter the outdoor weather conditions. Remember that the only time your HVAC system is removing moisture is when the air conditioner is running. This is very important because when we have beautiful weather and during the winter, the air conditioner is not running, but moisture is still being generated inside of our homes. The moisture sources are us, pets, plants, cooking, and bathing. It is best to have a proactive approach on how to address the moisture such as exhaust fans and building a very tight thermal envelope in addition to the dehumidifier.

The standard air-handler is only capable of running at one speed and does not have the flexibility that the variable speed unit has. Although it is less in cost, there is a major sacrifice in performance and additional benefits in our hot humid climate. The best thing would be to bite the bullet and do both.

Good luck.

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greentangent said...

Not only there are variable speed air handlers but also variable speed compressors which are present in the outdoor units of a central air conditioning system and are again energy efficient and give comfort cooling. Thanks for the informative blog.

Anonymous said...

Hi Paul what is the typical cost of variable speed blowers?

Brielle Franklin said...

This is great information. My boss and I have been looking for a air handler rental for our office. We had no idea what the difference was. Thanks so much for clearing it up for us.