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What size air conditioning unit do I need for my home?

Air conditioning
Photo Credit: Piman Khrutmuang

When installing an air conditioning system in your home, you must choose the right size capable of managing your home’s cooling needs. By size, it doesn’t mean the physical dimensions of the air conditioner. Instead, it refers to the appliance’s cooling capacity measured in British Thermal Units (BTUs).

The right size air conditioning system will ensure efficiency and lower operating costs. An AC that is too big for your home quickly cools your home and shuts off. For a while, the room will be nice and cool. Unfortunately, heat will infiltrate your house, forcing the AC to restart. The on and off-cycle drives up your electricity bill.

On the other hand, an AC that is too small will continuously run to cool your home. As a result, your electricity bill starts to skyrocket.

Factors to Consider When Choosing an Air Conditioning System

There are several factors to consider when choosing an air conditioner. They include:


At times, cheap can be expensive. The most costly units prove to be cost-effective in the long run. They tend to consume minimal energy and, in the process, lower the electricity bill. Most importantly, you should consider your budget when choosing an HVAC system.


The air conditioning system you choose needs to be durable. It means it does not require frequent repairs or replacement. Before purchasing your preferred brand, make sure that you do in-depth research. If you are still confused, check out the Rockwall air conditioning website.


When installing your air conditioner, ensure that you install it in a place where it can cool the room efficiently. Avoid placing it in bright areas, as this can overheat the system. Also, ensure that the surrounding area is clean for efficiency.

The Size of Your House

The size of your house will dictate the size of the air conditioning system you will choose. You must consider the number of rooms you have, the square footage you need to cool, and the number of individuals residing in your house. The more the number of individuals, the bigger the air conditioner.

Efficient Ductwork

Before choosing an AC system, it is advisable to check whether the ductwork is in good condition. The ductwork controls air quality, temperature, and airflow. Worn-out ducts leak almost 20% of cold air into the surrounding environment.

Number of Windows

If your house has many windows, it means that there is adequate air circulation. Therefore, you will need a small-sized air conditioning system.


Before buying an air conditioner, you need to ask yourself if the walls and ceilings are properly insulated. Also, do you have a basement or an attic in your home? Proper insulation makes your home thermally efficient.

Climate zone

The climate in your area of residence will dictate the size of your air conditioner. You will require a large AC system if you live in a geographical area with high temperatures.

Determining What Size Air Conditioning System You Need For Your Home

Selecting the ideal size of an air conditioner you need for your home can be a bit challenging. Fortunately, many professionals can help you choose the right size using the following methods:

Approximate Calculations

Even though you can do this by yourself, it is advisable to hire a professional HVAC contractor. This method helps you estimate your air conditioning unit’s size using simple calculations, such as determining the base BTU and square footage.

Determining the Square Footage

The first step is to determine the square footage of your home. If the number is not written down somewhere, you can achieve this by measuring the room’s width, length, and height using a tape measure. If there are several rooms, calculate the square footage of each room and add them all together.

Determining the Base BTU

British Thermal Unit (BTU) is the unit used to measure the amount of energy used by air conditioners for heating and cooling. According to experts, 25 BTUs are the approximate amount of energy required to cool your house’s square foot. To determine the base BTU, multiply the square footage of your home by 25 BTUs.

Additionally, in this method, you need to consider the height of your ceiling. If your ceiling’s height is more than 8 feet, multiply the base BTU by 25%. To determine the tonnage required, divide the number by twelve thousand.

The Manual J Calculation Method

This is the method that most professional air conditioner contractors use to determine what size air conditioning unit you need. Its primary purpose is to calculate the cooling and heating requirements of your home. The manual j calculation method helps a technician determine the exact size air conditioner to install in your house for optimum efficiency and comfort.

A professional HVAC technician can make the proper measurements and, as a result, design a system that concurs with your climate control needs.

Many HVAC companies offer the above audit services. Therefore it can be daunting to find the most professional and reliable one. An inappropriate energy audit wastes your money, time, and energy. To hire a reliable auditor, ensure that you do the following:

  • Ask for recommendations and referrals from friends, relatives, or neighbors.
  • Check online reviews.
  • Make sure that they utilize a calibrated blower door.
  • Confirm where they carry out thermographic inspections.
  • Check if there are any complaints against the contractor.
  • Confirm the necessary certifications.
  • Hire an auditor with the necessary calculation tools.

During a manual J calculation, you should expect the taking of measurements and a blower door test. The purpose of taking measurements is to acquire real data to determine your HVAC system’s size.

However, some technicians rely on the “rules of thumb” to make a decision. It states that the size of the air conditioning unit you choose should not exceed 15% over the recommended BTUs for cooling and 40% for heating.

The contractor will have to carry out a blower door test if there aren’t any other air conditioners in your home or infiltrated air.

Choosing the right size air conditioner for your home significantly impacts your energy bills and comfort. The process is critical, which is why it is advisable to hire a professional. Contact several technicians to choose the one that fits your budget.

augusta free press
augusta free press