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What Is the Cooling Limit of My Air Conditioner?

When the temperature soars in the summer, how much can your air conditioner cool?

What Is the Cooling Limit of My Air Conditioner?

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Matt Reed


Matt Reed


July 16th, 2021

We hear from you when it’s miserable outside, and we want to help. Extreme summer heat can test anyone’s patience. So when you turn to your trusty air conditioner for relief, it would be nice if you could tell it to cool you off as much as you desire.

Alas, it’s not always that simple.

It’s not a problem when the outside temperature is in the mid-80s, and you want the inside temperature to be in the high 60s, low 70s.

When it’s 90 or higher - and let’s not even consider how suffocating high humidity can be on top of that - your AC has limits.

If you’re sweltering, wondering whether your air conditioner is performing as well as it should, we have answers. We’ve been in thousands of homes where the inside temperature wasn’t up to the homeowners’ wishes, and we understand your frustrations.

In this article, we’ll explore what those limits are, ways you can make your house seem cooler when your AC reaches its greatest cooling capability, and we’ll even debunk a myth or two about cooling.

Why Is My Air Conditioner Not Working Like I Want It To?

Your AC has limits, no matter its age, how well it was installed, its manufacturer, etc. As a rule of thumb, when it’s 95 out, your AC can cool your house to approximately 70-80. Your air conditioner will be able to cool to about 15-25 degrees from the outside temperature.

If it’s 95 degrees outside, and you set your thermostat at 65 degrees, there’s almost no chance your system will get the indoors to 65 degrees.

If you have your air conditioner set to a temperature that makes that differential more than 15-25 degrees, you will likely run your AC all day long and still not reach those desired temperatures. This overuses a system that was not designed to accommodate what you are trying to do.

A thermostat.

Cranking the thermostat lower and lower will mean that your unit will run and run. It will keep the temperature at a stable setting, but it probably won’t go much below a 20-degree mark. At least not until the sun goes down. Meanwhile, your next electric bill you receive will reflect the constant usage.

We need to dispel a myth: Setting your thermostat lower does not increase the amount of cool air. Your blower can work at its optimal speed, and you can even use a whole-house dehumidifier to help get the moisture out of your home. That helps with overall cooling. But that temperature coming from your registers is the same, no matter if you set the thermostat at 75 degrees or 60.

According to the U.S. Department of Energy, the best indoor temperature for your home during the summer months is 78 degrees. As a rule of thumb, each degree set above 72 can save you up to 3% on your cooling costs.

It’s a tough choice. You can swelter indoors, but you can save money if you’re willing to settle for a higher temperature.

Related reading: HVAC Thermostats 101: Installation, Features & Controls

A Larger, More Powerful AC May Not Be a Solution

If your air conditioner is too big, it does something called short cycling. It will turn on and off prematurely, which doesn’t allow the fan to truly condition the air. For full conditioning to take place, the unit needs to circulate the air so that warm, humid air has a chance to travel through the return air ducts, and then get expelled outside.

A bigger-than-recommended system will cool your home too fast, and will leave you with a cold jungle: cool air, high humidity.

It will also lead to shorter life expectancy from your AC, due to its constant on/off operation.  The system would be the right size for the home only a portion of the year.

If your furnace fan can push and pull air throughout the house consistently, it will have a better effect on moving humidity around, which means a more consistent temperature in the house. This means the air conditioner won’t have to spend most of its energy on dehumidification and less on cooling.

Factors Preventing Your AC From Operating at Peak Capacity

If your AC is not reaching anywhere close to a 20-degree difference, several factors might be inhibiting its performance. They are:

  • Undersized unit
  • Improper installation
  • Leaking refrigerant
  • Dirty air filter
  • Poor insulation
  • Single-paned windows

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Undersized unit. If your HVAC contractor installs an undersized unit, proper cooling will be an issue. Your AC will run and run and run during the summer, and you still won’t feel adequately cool in some rooms of the house - especially upstairs.

Improper installation. Improperly sized ductwork can lead to hot (and cold) spots in your home, even with a new system. Static pressure due to improperly-calibrated equipment, poorly sized ductwork, or both is the main culprit if your old system died before it was 15-20 years old. Even if the final straw was something else, it often relates back to these pressures creating stress across the entire system.

Leaking refrigerant. This is easy to fix. Any HVAC technician can recharge your system with the correct refrigerant. But if the source of the leak isn’t repaired, they will come back to your house repeatedly. It’s a rip-off and can be avoided. A technician should find and fix the leak before recharging the refrigerant.

A filter issue would contribute to heating and cooling issues. If you have a dirty filter or a bad filter, airflow is restricted. That will make it seem hotter.

If your home is under-insulated, the coolness from inside will leak outside. Leaks around doorways, windows, and other places will not help, either.

Single-paned windows are obviously less efficient than double- or triple paned glass when it comes to retaining cool. A house with a lot of single-paned windows will be hotter.

Strategies to Keep Your House Cool

  • Strategic use of curtains and drapes
  • Zoning
  • Ductless mini-splits
  • Preventative maintenance
  • Proper circulation
  • Dehumidifier
  • A properly-installed new AC

A partial solution is the strategic use of curtains or drapes. In the morning, they can be shuttered on the east side, on the west in the evening. In this part of the hemisphere, closing off the south side of the house will also work. Keeping the sunshine out makes for a dark home, but it will be a cooler one.

You could try a zoning system in your ductwork, where sensors will send the message that a warm room needs more cool air, and the other rooms don’t. Then you should close the dampers to most of the rest of the house to allow more air conditioning into that warm room.

You can also create a zone with a ductless mini-split. That would create a system inside that room that is cooling only that room. It will also lower its humidity. The rest of the house will not benefit, unless you invest in a mini-split with multiple heads. They can have as many as five. This is not an inexpensive option.

  • A single-zone/one-room heating and cooling solution will range between $3700 and $6000.
  • A dual-zone/two-room system will run between $5,500 and $9,000.
  • A system that provides heating and cooling for multiple zones/three to eight rooms starts at $8,500 and up.

Preventative maintenance is one of the best ways to keep your HVAC equipment running at optimum capacity. You might be low on refrigerant or have a worn-out motor or a dirty evaporator coil. Some problems can reduce the AC's ability to run.

If you’re not getting proper circulation, then you may have something dirty in your ductwork. Maybe you would need to have your ducts cleaned.

Bad ductwork (and especially ductwork that has holes in it) can restrict airflow and cause some rooms to be at the right temperature while others suffer. No HVAC system, no matter how much you paid for it, can overcome this problem.

A dehumidifier can help your air conditioner to be more efficient. Excess humidity levels of 50% or more in our homes can make it feel clammy and warmer than it is. By lowering the humidity level, ideally between 35%-45% RH (Relative Humidity), we can feel more comfortable at a higher temperature. A room dehumidifier can help with especially damp spaces, such as a basement. A whole-home unit does exactly what the name implies.

You could supplement with window ACs that help a specific area. But if you have a full system in your house, and you’re supplementing it, something has gone wrong with your system, especially if the inside temperature has changed dramatically.

If you have an old blower motor, or you’re not running it very much, all you’re doing is letting humidity stagnate. You will feel warmer. If you have a variable speed fan, it’s going to help contribute to the cooling process. If we're moving the air around, and we don’t have so much humidity in certain areas, the air conditioner will have a cooler effect throughout the whole house.

Clean the coil. The coil on your air conditioner may be covered by cottonwood or grass clippings. It sucks in air, and if that whole filter looks like it has a sweater on it, it’s not breathing. Then there’s no way you’ll get the temperature drop you desire. Hose off the debris on the coil, and see if that helps.

And if none of these potential solutions to a sticky problem addresses the issue sufficiently, it’s time to talk to an HVAC professional about other options. If your existing AC isn’t capable of cooling as you’d like, and it’s 15 years old or even older, it's likely time to consider a replacement, or at least see where that option compares to others we've mentioned in this article.

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Does an Old AC Cool As Effectively As a New One?

If your AC isn’t new, it still may be as good as a new one. It’s all about the installation. If the refrigerant were done properly, it’s the right pressure and the right size, the temperature drop should remain the same.

The ability of the air conditioner to condense refrigerant should be much the same. It’s just not as efficient. It takes more energy to cool.

But you are dealing with a ten-year-old circulating fan. Like any motor, it may not be pushing as well as it used to, which could affect the inside temperature. The big difference is whether it is still able to circulate the air around the house the same as it did ten years ago.

What If It’s Only a Single Room That's Too Hot?

If the room is farthest away, it used to be OK, and now it isn’t, you may have something wrong with the circulation or there’s a leak in the ducts somewhere. Maybe the condensing unit is not doing what it used to do.

A one-room issue, if everything is working, is usually an airflow issue, or something’s dirty. If you’ve lived with a hot room for years, and that’s something you want to fix, it’s fixable.

Make sure that you are running your fan, even if the AC is not running.

If there’s an upper room of the house where hot air collects, and there’s no ventilation, you could put a dehumidifier in the attic. Basically, you need an electrical outlet and a drain, and then you could just duct it into the room below where it could have a return and supply.

Why is the Heat More Noticeable Now?

During COVID, when people spent more time at home, we did get asked to solve issues of comfort more. People who worked at home for the first time turned rooms that they normally didn’t use into office spaces.

Those are usually not the most comfortable rooms; that’s why they weren’t using them. A lot of lofts, a lot of upstairs rooms that weren’t used very much are now occupied spaces.

Rooms that were too hot haven’t changed. You’re now spending more time in them, so the heat is more unbearable.

What’s Next

A good HVAC contractor should be able to walk you through each and every factor that affects your comfort level.

The HVAC installation process is the single most important step for the safety and life expectancy of your system. It’s the difference between a long, efficient life and sub-par performance.

While you search for the best contractor for you, we encourage you to check out our HVAC contractor checklist below. We created this free, downloadable checklist based on HVAC industry best practices.

HVAC Contractor Checklist

And if you’re ready to speak with a sales representative, we’d love to help you find the best air conditioner for you.

At Fire & Ice, we take the time to understand your needs and comfort concerns. This helps us recommend ACs and other equipment that can customize your HVAC system to fit your preferences and lifestyle.

If you live in Central Ohio, click the “free estimate” button below to schedule your free, in-home estimate. We look forward to speaking with you.

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