How to tell if your HVAC unit isn’t working efficiently

March 11, 2021   By Terri Williams

How to tell if your HVAC unit isn’t working efficiently

When your HVAC unit is operating at its best, it heats and cools efficiently, providing a comfortable environment. However, according to the U.S. Energy Information Administration, heating and cooling account for 51 percent of the average home’s energy consumption. So, you can’t afford to have an inefficient HVAC – especially in Texas, which has earth-scorching summers but still requires heating in the winter.

Here are some of the ways to tell that your HVAC unit isn’t operating at peak performance.

It never reaches the thermostat setpoint

“Unless the outside temperature is above 96 degrees or below 0 degrees, HVAC systems are designed to be capable of reaching a wide range of setpoints,” explains Steve Kurtz, owner and operator of One Hour Heating & Air Conditioning. “Of course, as the outdoor temperature becomes more extreme, it will take longer for the system to reach the setpoint.” 

But, for example, if the setpoint is 72 degrees, and it never reaches that temperature, Kurtz says the issue should be investigated.

The HVAC filter is dirty

The HVAC filter is often neglected, but a lack of TLC can have serious consequences. “The role of an HVAC filter is to remove debris from the air before it enters your system,” says Marla Mock, VP of Operations at Aire Serv.

Mock explains your filters can get dirty as a result of air pollution, pet dander, or even dirt near the vents. “When things clog up, the unit will have to work much harder and use more energy, causing a substantial rise in the energy bill,” she says.

And if that’s not bad enough, she notes that dirt in the filter can also cause other problems. “It can shorten the life of your HVAC system because dirt pulls into the inner workings of the unit,” Mock says. “Strain on the fan motor from the increased effort will take its toll, as well.”

According to Mock, you should replace your air filters at least on a quarterly basis, but maybe more frequently if you have pets or allergies.

The system never stops running

On hot days, it may take a while to cool down your home. “However, for example, if the temperature is in the 80s outside, and the AC is running constantly, there is a problem,” says Kurtz. “A professional can identify if a refrigerant leak has developed, which is a common problem that causes high energy bills and severe lack of comfort on hot and humid days.” 

However, Kurtz says there’s one exception to this rule: if you own a 2-Stage or Variable Capacity AC. “These high-end systems are designed to run at low levels for longer periods of time, creating maximum comfort and stable indoor humidity levels,” he explains.

You have a clogged drain line

 A clogged drain line is another sign that your HVAC isn’t working efficiently – and Mock says it could also result in a more humid environment. So, how would you know if your drain line is clogged? 

“Standing water and water damage around the indoor part of the unit could be a red flag that you have a clogged drain line and should call a licensed service professional as soon as possible to clear it out,” Mock advises. You may also detect a moldy or musty smell either near the unit or coming from the vents or registers.   

There’s debris around the outside unit

Debris around the outdoor unit can be the contributing cause of a clogged drain line and also lead to other issues. 

“Check the outdoor unit once in a while and if you see there are leaves, grass, twigs, and other debris around it, go ahead and carefully clean it,” Mock says. “The basic rule of thumb is that the unit should have a minimum of 12-24 inches clear on all sides.” Without this level of clearance, the overall performance of your HVAC unit can suffer.

The thermostat is malfunctioning

Your home’s thermostat can also contribute to your HVAC unit’s efficiency. “Your family should not have to sort out a broken thermostat,” Mock says. “Your HVAC system, including your thermostat, needs to work quickly and efficiently when you need it most.” 

There are a number of ways to determine if the thermostat is malfunctioning. “If it is blinking, displaying an error message, or the room feels hotter or colder than the temperature you set on the thermostat, consider resetting it or replacing the batteries,” Mock says.

It’s making noises

As a general rule, your HVAC unit should be pretty quiet. “A noisy system is never a good sign,” warns Tommy Dutton, franchise consultant at Aire Serv. “Can you hear it running from a block away or does the air circulating in and out of vents whistle or whine or sound like a windstorm inside of your home?” 

If this is the case, Dutton has bad news. “There is a good chance it’s nearing the end of its lifespan,” he explains. 

It’s near the end of its lifespan

If the system is 10 years old, Dutton says it’s a good idea to think about replacing it once it’s out of warranty. “If your warranty has expired, Murphy’s Law can kick in at any time and problems always seem to surface at the worst possible time – like overnight, during the weekends, when you have company over, or as you’re getting ready to go out of town,” he says. 

Your energy bills are higher

Admittedly, now that we’re all spending more time at home during the pandemic, your energy bills have probably increased. However, once you factor in that change – perhaps by comparing current bills with other pre-pandemic times you’ve been at home all day (like during the holidays), check to see if your energy bill is unusually high. 

“High energy bills can be reflective of a system that needs to be replaced,” Dutton says. “If your system is inefficient, you might be paying money to the utility company that could be better spent on a more comfortable, high-efficiency system.”


Terri Williams is a freelance journalist with bylines at The Economist, USA Today, Yahoo, the Houston Chronicle, and U.S. News & World Report. Connect with her on Twitter or LinkedIn.