Why your new AC is struggling to keep your house cool

If you’re feeling hot, sticky and just all-around uncomfortable come summer, that’s a problem.

There are a few things more frustrating than spending thousands on an HVAC/AC system and finding that it just does not cool your space. This might not mean that the unit itself is broken and needs replacing. In fact, it could be a sizing, ductwork, airflow or even installation issue causing the lack of cooling.

Here’s why your new AC may not be cooling your home the way it should — and what to do about it.

Your AC may be the wrong size for your home

Sizing is one of the biggest issues. Homeowners assume that a larger size automatically means better, but that’s not necessarily the case.

“First of all, it needs to be sized properly,” says Gregory Milich, an HVAC expert and college instructor with 43 years of experience. “You can’t just take a three-ton system out and put a four-ton system in because the customer says, ‘I just want more air conditioning.’ It does not work that way.”

According to Milich, homeowners cannot simply swap in a larger system because they want more cooling. The system needs to be matched to the home.

If the system is too small, for example, it may run consistently and not actually cool your space. If it’s too large, it may not dehumidify properly. That can leave your home feeling cold in some areas and damp, sticky or uncomfortable overall.

Milich says to avoid unnecessary mistakes, your best bet is to have a contractor evaluate your home to determine what’s best for you. Josh Conder, division operations manager for ARS Central Division, says his team does a full energy analysis and heat-load calculation to determine what works best for each home.

“We go to the home and do a full energy analysis and a heat-load calculation to determine what really works best for their individual situation, as opposed to just throwing out a blanket price and hoping that it works,” Conder says.

Your ductwork could be holding the system back

You could have a brand-new AC, but if the ductwork is poorly installed, you might feel like your system is not working properly.

If the ducts are leaking, restricted, poorly sealed or not sized correctly, you may not get the airflow or efficiency you paid for.

“A lot of the real problems come from ductwork,” says Joey Dooley, a general manager at ARS in Texas. “If the ducts are installed improperly, if there are restrictions, if things are sealed badly, then you’re not getting the efficiency you paid for. For example, we can change to higher-efficiency equipment, but if the airflow and duct system aren’t right, you’re not going to get that full efficiency.”

What does this mean? It means your AC is working way harder than it should to cool your home. According to ARS service data, ductwork repair or replacement typically runs between  $2,800 and $4,000 per job, depending on the extent of work and the home’s layout.

Make sure your ductwork is set properly when you first install it. It will save you tons of money in the long run.

Your system may not have been installed correctly

Speaking of installation, this goes for your whole system overall. Even high-end equipment will underperform if it’s not installed correctly.

“An HVAC system is not complete until it’s installed correctly,” says Scott Urquhart, an HVAC sales and customer experience expert. “Whether it’s the greatest equipment with the greatest warranty in the world, or it’s the cheapest equipment you’ve ever found or heard of, you have to install it correctly. And if you don’t, you’re going to have problems.”

The same thing also applies to performance.

“I tell people all the time that the equipment can be great, but if the installation is bad, the performance will be bad,” Dooley says.

This could be a bad installation of the ductwork, wiring protection, sealing and the airflow setup. A shoddy installation might not show up immediately, but you’ll start to notice signs in the form of your room not cooling correctly or higher energy bills.

Your AC may not be controlling humidity

Milich says air conditioning is not just about cooling.

“Air conditioning is dehumidification with a byproduct of cooling,” he says. “So air conditioning is basically dehumidifying the air.”

Since ACs are supposed to remove moisture from the air, if they’re installed incorrectly or oversized, they’re not going to function properly. If you notice that the house still feels uncomfortable even if the thermostat shows the temperature as accurate, the new AC is not controlling the humidity. 

Milich also warns that homeowners should not simply shut off their system when they are not home.

“It doesn’t just have to do with cooling,” he says. “It’s the humidity that will hurt — not hurt you, but hurt your belongings in your house. Humidity soaks into everything.”

Your filter or airflow may be the problem

A dirty filter, a blocked filter or even an old filter can make it harder for your AC to move air through the home.

If you’ve got a newer HVAC system, it’s possible that it will automatically tell you when your filter is dirty.

“There are even systems now that can help tell you if a filter is actually dirty versus replacing it just because it’s ‘time,’” Dooley says. “If you’re buying expensive filters, replacing them when you don’t need to is unnecessary.”

If your new AC is struggling, checking the filter and airflow is one of the easiest places to start.

Your home may have hot spots

If some rooms stay cool while others feel warm or your home has hot spots, it may be your home’s layout, ductwork, insulation, windows or airflow balance. A new AC can only do so much if the cool air is not being distributed evenly.

This is definitely a bigger issue in larger homes where the ducts are not routed properly or are too small/leaking. It can also happen if certain rooms have more sun exposure, larger windows and poor insulation.

This is why a proper home evaluation matters before you install anything. The unit must be properly fitted for your home.

Your AC may have drainage issues

Since an AC pulls humidity from the air, it also creates water. That water needs to drain properly. If the drain line is clogged, backed up or poorly installed, it can affect system performance.

“I think sometimes people don’t realize how much water an AC system produces, and how quickly that can become a problem,” Dooley says. “Those systems can generate a lot of water, especially in the summertime, and if drainage fails, you can get serious damage.”

Any water dripping, pooling around the AC or even musty odors are a red flag and something to inform your technician about.

Your thermostat may not be helping

If your thermostat is near a sunny window, kitchen, drafty area or vent, it may also be getting a temperature reading that does not reflect the rest of the home.

“Back in the day, you had a little thermostat on the wall that had a couple of numbers on it,” Conder says. “You could slide in between them, and now your thermostat can give you a warning if something is going wrong with your system. It can notify us and say, ‘Hey, I don’t know if you saw this, but it looks like this is happening with your system.’”

What to check to see if your new AC is functioning properly.

How much could a replacement cost if the system is wrong?

If your new AC is not cooling properly, start by diagnosing the problem. Don’t assume it automatically needs replacing, as that could be a costly mistake.

According to ARS, a complete residential HVAC system replacement typically ranges from about $12,000 to $16,000, depending on system type, home size and installation requirements. ARS notes that simpler furnace-only replacements cost less, while premium or high-efficiency systems and complex installs are more expensive. 

According to ARS, a central AC split-system replacement typically ranges from about $13,000 to $16,000, with cost driven by system size, efficiency and install complexity. ARS reports that a combined gas furnace and AC system typically runs between about $13,000 and $16,000, depending on equipment and home requirements.

Why AC quotes can vary so much

If you’re trying to fix a cooling issue, you might get two contractors providing two drastically different quotes.

According to ARS, two HVAC quotes for the same home can come in thousands of dollars apart, and it’s typically not because one contractor is overcharging. ARS points to equipment tier, efficiency rating, install complexity, and whether work like ductwork or electrical upgrades is included as the main drivers.

This means that one quote might look cheaper on the outside, but it’s important to check whether the equipment is up to par and whether there are any hidden costs, like installation fees, not included.

What to ask your HVAC contractor

If your new AC is not keeping your house cool, ask direct questions before spending more money.

Ask your HVAC contractor:

• Whether a heat-load calculation was performed
• Whether the system is the correct size for your home
• Whether the ducts were inspected, sealed or replaced
• Whether airflow was tested after installation
• Whether the system is removing humidity properly
• Whether the thermostat is placed correctly and communicating with the system
• What warranties or guarantees apply if the system is new and not performing as promised

Urquhart says homeowners should look for a company that offers a money-back guarantee.

“The most important advice I can give people shopping for HVAC systems is to make sure to go with a company that offers a money-back guarantee,” he says. “You get to run this system for a year, and if there’s anything you don’t like about it, the company has to make it right.”

Our verdict

If your new AC is struggling to keep cool, don’t automatically assume it needs to be replaced. A new system can still underperform if it is the wrong size, poorly installed, connected to bad ductwork, struggling with airflow or failing to control humidity.

Start with the basics: Check the filters, vents and thermostat. Then ask an HVAC professional to look at sizing, ductwork, airflow, humidity and drainage. If your system is new, ask what warranties or guarantees apply.

A new AC should make your home comfortable. If that’s not happening, it might be time to call in a professional.

FAQ

Can a new AC be too big?

Yes. A system that is too large may cool the air quickly but shut off before it removes enough humidity, leaving the home feeling damp or uncomfortable.

How often should a new AC be maintained?

Dooley says biannual maintenance is the baseline in many cases, and many manufacturers recommend it. Regular maintenance can also help protect your warranty.