How Long Does An AC Take To Cool An Apartment House?

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Is your AC undersized or oversized to my room? Is it consuming too much electricity while running long? Should I replace the AC unit? 

It’s obvious to get blown away by such questions in your mind if you don’t know exactly how long an AC takes to cool your room or house. As it’s not printed on the manual, you can’t really get the answer right away. 

Luckily, we’ve figured out the accurate time central/inverter/portable/window ACs take to cool 5°F, 8°F, 10°F, and 20°F. For any question that pops up in your mind about these, we’ve got an answer. 

Let’s jump into it- 

AC Cooling Time- What Are The Deciding Factors?

Before we jump into the answers, let’s address the factors that affect your AC unit’s cooling time and efficiency. There are 4 most important factors such as- 

House Insulation and Ductwork Condition

It’s an HVAC 101 that if you let the air escape from holes, cracks, and gaps in the house, it’ll take longer to cool. 

Hence, the cooling time depends a lot on how insulated your doors, windows, attic and ductworks are. 

In an ideal case scenario, a properly insulated house will look like this- 

  • Perfectly air-tight frames and casings for doors/windows. 
  • Ductworks covered by high R-value insulators like spray foam, foam, Rock Wool, Fiberglass, etc.
  • Leak-free penetrations(pipes, wires, etc) through the walls.
  • Insulated attic fans and exhaust fans.

The more you’ll go otherwise, the longer it’ll take your AC to cool your home. Period.

The Outside Weather

It goes without saying that the hotter the climate is, the harder and longer AC takes to cool your home. If the humidity is high as well, it takes even longer. 

For example, it’d take way longer to cool 10°F of temperature in Houston in the months of July than in Seattle at the same time. 

But it’s a good thing that ACs are designed as per the locality’s climate. It’s called the Design temperature by ASHRAE.

House Sq. Ft. vs AC Capacity

No matter what kind of house or apartment you have, the estimated AC capacity is fixed. If you go beyond or lower than that, the heating time will be unusual. 

Let’s learn how to measure both, followed by the standard relation between them- 

The sq. ft. of your house is simply the floor area the AC has to cover. Single central air can cover up to 2000-2100 sq. ft. For window or portable ACs, it’ll be single rooms within 100-800 sq. ft size.

Next, AC capacities are measured in BTU. And AC sizes are labeled as Ton. Usually, 1 Ton is equal to 1200 BTUs.

Once you know the sq. ft. of your house and the AC BTU, here’s the compatibility formula- 

For Hot Climate, 25-30 BTU/Square Foot of Space


In a 1200 sq. ft. house in warm states like Arizona,

Required Central AC Size: 25 BTU x 1200(sq. ft.) = 36,000 BTU

Required AC Tonnage: 36,000/1,200 = 3 Ton(up to)

For Cold Climate, 20-25 BTU/Square Foot of Space


In a 1200 sq. ft. house in cold states like Utah, 

Required Central AC Size: 20 BTU x 1200(sq. ft.) = 24,000 BTU

Required AC Tonnage = 24,000/1,200 = 2 Ton(minimum)

To ensure a proper runtime and cycling of your AC, cross check these formulas and make sure you correct sizing.

Condition of The AC

Air conditioners age. And lose up it’s efficiency. You can’t expect the same kind of cooling period after 2 or 4 years as before.

Apart from wearing out, there might be some health casualties as well that might affect its cooling. Have a look- 

  • Dirty, clogged up air filter. 
  • Wrong size selection of air filter.
  • Dirty coil. 
  • Dirty blower with improper blower speed. 
  • Inadequate refrigerant, etc. 

Remember, Cooling Time for The First Time is Longer

Suppose, you’ve returned home after a few hours while the AC was turned off. Once you turn it on again, it’s not only the heat of the air that it has to fight against. The walls, ceilings, furniture- everything is hot! 

Hence, your AC would take a longer time to drop the air temperature noticeably. It has to cool down those ‘extra’ heat first, right?

Technically speaking, those extra heat are of three kinds-

Latent and Sensible Heat

Collectively known as ‘Cooling Loads’. It defines the initial heat that has to be removed to circulate around a comfortable temperature inside the house. 

Radiant Heat

Heat radiated from hot objects around. Fireplaces, heaters, etc radiate more of this heat. 

That said, it’s okay to take longer than what it’d take later on. In case you’re curious about if the AC’s functioning properly, you can go for this quick test- 

Take a thermometer and measure the temperature of the hot air coming into the return. Do the same and get the cool temperature that’s coming through your room’s inlet. If the temperature gap is around 20-degree, your AC is in good health. 

How long To Cool 5/8/10/20°F With A Central AC?

As central ACs are what most home dwellers prefer, let’s break down the cooling time of central ACs first. With a ground-rule in our mind, we’ll actually go through several cooling case scenarios and the required times for that. 

Have a look at the ground rule of central AC cooling first- 

1.15 Hours/Degree: The Ground Rule for Central AC

If your central ac is a proper match with your house’s square footage, then it should take 1 hour 15 minutes to cool down by a degree(1°). You can call it a ground rule for the cooling time of most central ACs.

However, this is just an ideal case scenario and depends on a lot of things. Mostly, for different outside temperatures, the cooling speed will differ. Hence, we’ve created individual cooling time analysis for 5, 8, 10, and 20 degrees of cooling extent. 

Have a look- 

How Long An AC Takes To Cool from 80°F to 75°F/5 Degrees?

A central AC would take about 4-6 hours to cool down 80°F to 75°F/5 degrees of temperature. Of course, the BTU of cooling capacity has to match the house’s size. 

Usually, cities in warm climates like Los Angeles get around 79-90°F around the months of June-July. Higher altitude states like Las Vegas hit that temperature even earlier(March-April). Therefore, bringing the temperature back to 75°F would take 4 hours of work in those situations. 

How Long An AC Takes To Cool 80°F to 72°F/8 Degrees?

On average, it would take about 6-8 hours for a central AC to cool 80°F to 75°F(8 degrees) inside your house. This is shorter than the usual case because once the first few degrees of temperature is brought down, the rest of the cooling process takes less time. 

An ideal example of this would be to bring the temperature from 80°F to 72°F when you want your home to be a little chillier than usual. 

How Long An AC Takes To Cool A House 10 Degrees?

On an extremely hot summer day(85-90°F), you can expect your AC to take about the whole day(8-10 hours) to cool 10 degrees and bring it back to a comfortable 75-80°F. 

During the months of May-June, Las Vegas, El Paso, and Denver dwellers might need to do this a lot. It often stays about 85-90°F outside. 

How Long An AC Takes To Cool A House 20 Degrees?

20°F of cooling is a lot, even for a powerful central AC. It would take about 12-15 hours for it to cool a whole house by that kind of temperature. 

But during the months of July-August, residents of Dallas, Houston, or such warm cities would like to do that a lot. Because the temperature is almost 95-100°F outside by then. Can’t blame if someone wants it to be in a comfortable 75-80°F home atmosphere. 

Cooling Time Needed For Other Kinds of ACs

Though central ACs are the most popular ones, they’re not the only choice. People also do use individual units like inverter ACs, window ACs, and sometimes, portable ACs as well. Here go the average cooling time calculations for them- 

How much time does the inverter AC take to cool the room?

Individual ACs like inverter ones have to cool a smaller area compared to central AC. 

If the AC’s tonnage is compatible with room sq. ft., then you can expect an inverter AC to bring down 10-degree of temperature in 15-20 minutes. 

Note that, unlike non-inverter ACs, inverter ACs don’t switch off at all. They keep running the compressor at a slower pace and don’t let the room temperature drop significantly. Hence, an inverter AC cools fastest and maintains the temperature better than a non-inverter AC. 

How long does it take for a portable AC to cool the room?

If a portable AC unit is of appropriate cooling capacity for your room, it’d take about 20 minutes to cool 5 degrees(90°F to 85°F). Compared to window AC units, it takes much longer to cool to the same extent. 

How long does it take for window AC to cool the room?

The good old window AC units take about 20-40 minutes to cool 5-degrees of temperature, and an hour for 10 degrees. Compared to inverter ACs, that’s slower and more energy-consuming. But compared to portable ACs, that’s somewhat faster. 

Frequently Asked Questions

How long should it take to cool a house from 80 to 68?

To cool a house from 80°F to °F(12°F), it would take about the whole day or 8-12 hours for a central AC. If it’s quite humid out there, this might take even longer.  

How long should it take to cool a house from 90 to 72?

To cool from 90°F to 72°F(18-degrees), it would take about 10-12 hours for an average central air conditioner. Based on insulation, ac health, this might also vary. 

How long should it take to cool a house from 90 to 75?

A central AC unit would take about 8-10 hours to cool down a house from 90°F to 75°F. Sometimes, it might take longer based on the insulation, humidity, and some other factors. 

How long should it take to cool a house from 75 to 70?

To cool 5°F or from 75°F to 70°F, a central AC should take 3-4 hours usually. As 75 degrees is not such a high temperature, the latent/radiant heat and the sensible heat will be quite less. 

How long should it take to cool a house from 72 to 68?

For cooling 4 degrees from 72°F to 68°F, a central AC would take 2-3 hours usually. If the sensible heat and cooling load are not that much, it might take even shorter. 

How long should it take to cool a house from 2 degrees/77 to 75?

To cool down by 2 degrees or 77°F to 75°F, a central AC would take 1-2 hours at best. Once it has started, it might take even shorter for the next 2 degrees of cooling.

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2 thoughts on “How Long Does An AC Take To Cool An Apartment House?”

  1. Ducts are conduits or passages used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air. The needed airflows include, for example, supply air, return air, and exhaust air. Ducts commonly also deliver ventilation air as part of the supply air. Typically, a service provider will use specialized tools to dislodge dirt and other debris in ducts, then vacuum them out with a high-powered vacuum cleaner.

  2. House size and air conditioning capacity are two factors to consider when deciding whether or not to install an air conditioner. For example, a house with smaller square footage may need less air conditioning than a larger home because the smaller house can hold its temperature more easily. On the other hand, a home with inadequate air conditioning may experience high cooling costs due to high electricity bills.

    According to the Energy Information Administration, an AC unit taking about 8 hours to cool an apartment house will cost about $0.10 per operation hour. Therefore, if your apartment house has an AC unit that runs for eight hours each day, your monthly energy bill will be $40.40 ($0.10 x 8).


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