Many readers of our best portable and window air conditioner installation Chicago evaluations have asked us, “How Many Air Conditioner BTUs Do I Need?


The solution is complicated! You’ll need to know how big your room is to choose the right size air conditioner, but you’ll also need to know where the heat in your room is coming from. The heat that enters your home through sun-facing windows is distinct from the heat that naturally circulates throughout your home on a hot day. When considering air conditioner sizes, feel the humidity outside as well as what you intend to do inside.

Window Air Conditioner Size Calculation

A window air conditioner is the easiest to use because it only cools one area and is very efficient. A calculator widget based on Energy Star recommendations will inform you what size to buy.

How Many Air Conditioner BTUs Do I Need?

Because 8,000 BTU units are the most popular, we focused on them. Just because you can find and buy an air conditioner doesn’t mean it’s right for your room. Take the time to choose the right size to avoid the hassle.


Knowing how much capacity you need requires knowing the heat source. Extra persons in a room produce 600 BTUs of heat per person. Brighter rooms use 10% more BTUs. The inclusion of a kitchen increases the suggestion by 4,000 BTUs.

Selecting the Correct Size for Split AC Systems

The primary distinction between a split system and a window system is that split-system installation necessitates drilling holes, running coolant and drain hoses, running dedicated electrical cabling, and hanging the gear from your walls. The system is also more expensive, to begin with, costing three to five times as much as a window air conditioner for the same BTU capacity.


Split-system or “ductless” air conditioners are the exact sizes of window systems. It’s still only chilling one room, and you’ll have the same humidity issues if it cools too quickly. If you’re cooling a large area, it’s much easier to get a large ductless air conditioner that can cool more than 1,300 square feet of space, and you have more choice to position it in the most effective airflow location.

Choosing a Central Air Conditioner Size

From room air conditioners to large systems, calculations get harder. HVAC systems use a central fan to move air through ducts to cool or heat each room.


The form and size of your home’s ductwork determine the requirements for the central fan (or “air handler”). Certain systems may require extra circulating fans to keep a building at a steady temperature.


You must also modify your central air conditioner’s capacity to match your climate. 1.5 tons per 1,000 square feet is a general figure for air conditioners. Even though Florida and Nevada have similar summer temperatures, Florida homes need more conditioning and have different humidity challenges.


DIY HVAC parts are available, but a contractor can help you install a system that meets your needs. Although it’s not required, HVAC technicians in the U.S. are certified by NATE or HVAC Excellence. It’s not easy to find a bonded local contractor who can examine and service your system for 20 years, but it’s worth asking for references.

Choosing a Portable Air Conditioner Size

Portable air conditioners operate differently than other systems, and there are a few factors that make purchasing them in most circumstances a bad idea:


  • Portables consume significantly more energy than window units and do not effectively chill rooms.
  • When the temperature outside exceeds 85 degrees Fahrenheit, single-hose air conditioners will heat your space.
  • In most cases, tower fans outperform modest portable air conditioners.
  • So, if nothing else works, acquire the largest, quietest dual-hose portable you can afford.


Window air conditioners are quieter and more effective if you can install one. If you don’t mind the noise, portable air conditioners can work below 90 °F.


We tested them in a bedroom, living room, and office. A 12,000 BTU portable works in a 200-square-foot bedroom, while a 14,000 BTU device can cool 400 square feet if you can stomach the noise.


Running most portable air conditioners will make your situation worse if you have to weather a severe heat wave.


Unlike other air conditioners, the condenser coil and compressor motor are in your room. Portable air conditioners become difficult to remove as they heat up. Over 14,000 BTU portables are uncommon.


Self-contained air conditioners can only vent condenser coil and compressor heat through a window. This works well up to 85°F but isn’t as efficient or silent as other methods.

What is the source of the air?

If the portable AC has only a vent hose and no air input hose, the air streaming out the window is cooled air. Hot external air will replace it through cracks, doors, and windows. When exterior temperatures approach 85°F, a portable air conditioner can’t absorb enough heat to compensate, and the indoor temperature rises.


Dual-hose air conditioners employ a dedicated air intake line to keep cooled air in the room. Even if that problem is remedied, a portable air conditioner has limits: The energy department cuts the big ARC-14, which can technically collect 14,000 BTUs, to 9,000 BTUs.


12,000 BTU single- and dual-hose air conditioners were tested against an 8,000 BTU window unit at 97°F. Nonsense. Inefficiencies make portable air conditioners unsuitable for temperatures exceeding 85°F. A louder, larger portable fan, like the Whynter ARC-14, can circulate air in a larger room.

What Happens If The Unit Is Too Large?

Huge air conditioners are humid. Humidity makes air hotter. We refer to “relative humidity” rather than air moisture. In July, 10% relative humidity desert air contains more water than 30% relative humidity in winter evenings.


When relative humidity is 100%, the air is holding all the moisture it can, and a rapid drop in temperature will drive the water out of the air, like when hot shower air collides with a mirror, leaving a heavy fog.


A/C eliminates humidity as it cools the air. Heat is transported from the air to the evaporator coil’s extra-cold fins. Excess humidity condenses on the fins.


  • But AC size matters: Air heats up before water. The graph above shows the temperature and humidity in a 115-square-foot bedroom with an 8,000 BTU air conditioner, which absorbs 30% too much heat.


The air conditioner turned off when there was still excess water to extract. The air conditioner cooled any heat that built up or leaked into the room, but as the walls and furnishings became colder, the humidity problem intensified. Over time, water may condense on the room’s cool surfaces.

Dry Mode Is The Solution.How Many Air Conditioner BTUs Do I Need?

If you need to chill in a tiny room, you might not be able to find an air conditioner with the “proper” capacity – 5,000 BTUs is usually the lowest model. However, some air conditioners provide an alternative setting that reduces the fan speed to assist counteract the difficulties. Because your air conditioner will have to operate for longer to reach your desired room temperature, water will have more time to condense out of the air as it goes through the coil.


Because the compressor consumes the majority of air conditioner power rather than the fan, “dry” modes use almost as much power as regular settings but cool more slowly. Purchasing a larger-than-necessary air conditioner will result in higher electricity costs as well as the original cost of the equipment.


Contact our Mr. Quality AC repair specialists at (708)748-1946 today for more knowledge and assistance on HVAC. Visit our domain if you’re one of many asking yourself “What Size Air Conditioner Do I Need For 1500 Square Feet?”. We can help with that as well!

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