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Whenever there’s a conversation about air conditioning or heating, you would have heard people refer to BTU. Its definition is British Thermal Unit that ultimately measures the effectiveness of the HVAC system. To further define BTU, it refers to the amount of thermal energy that’s required to either cool or heat the temperature of one pound of water by a single degree Fahrenheit. When shopping for a new air conditioner, you need to ask relevant questions such as, ‘how many BTU per square foot do I need?’.


What Is BTU?

In terms of air conditioners, the BTU rating determines how much heat the system will remove from the air in a room per hour. The higher the BTU rating your system has, the more powerful it is during operation. However, it’s critical to understand that installing a larger system for a small room isn’t necessarily a positive.


What Happens With the Incorrect Size System

HVAC systems, particularly air conditioners, come with different BTU ratings, which means they have varying capabilities. A cooling unit that’s too large for the space will result in a waste of energy. Since the system decreases the indoor temperature faster than usual, the air conditioner will continuously start and stop to keep the air at an ideal temperature. HVAC technicians refer to this issue as short-cycling, which causes excessive wear and tear on the equipment.

Conversely, acquiring an air conditioner that’s too small for a space can lead to other problems. The first issue is your house will never be at the optimum temperature simply because the system doesn’t have the capacity. Secondly, when the system starts overcompensating for its lack of BTUs, it will drive your energy bill up and cause several parts to malfunction ahead of time.


The Calculation

To gain a clearer picture of how big or small a system you require, a technician must calculate the cooling or heating capacity to ensure proper comfort levels of the occupants. Professionals refer to this as the load of the home. A true calculation of the load of the home goes beyond the size and factors in other elements such as location and position in relation to the sun, amongst others.

If you had to calculate the size of the HVAC system on the size of the space, you’d have to assign around 20 BTU per square foot of living area. Room height, windows, shade, and insulation are other factors that dictate what BTU rating you require for your home.

Additionally, the home’s electrical system must meet the system requirements. Usually, room units require 120 Volt or 240 Volt circuits, while standard equipment requires 12 Volt outputs.


The BTU Formula

The first step to an efficient, powerful air conditioner is identifying the region’s climate. Southern states are more prone to humidity and would have to factor this into their calculation. Once you do that, you’d need the square footage of your property. You can find this information on a blueprint or closing documents. Alternatively, conduct the measurements yourself by multiplying width and length for all rectangles within the home.

Add those totals to have a figure. Check the home’s insulation to ensure that everything is in excellent condition. Evaluate your sun exposure and how much coverage you receive from trees and surrounding components.

HVAC contractors use a rule of thumb to allocate 20 BTUS to every square foot of space inside your home. For example, if your room is around 2,000 square feet, you’d require a system with a BTU rating of 4.3 out of 5. If you’re still struggling with finding the correct BTU rating for your air conditioner, perhaps this table could shed some light.

Room/Area Size BTU Capacity Type
200 sq ft 9,000-11,000 BTU Rooms that are 10×20, 12×12, or 15×15
400 sq ft 18,000-22,000 BTU 20×20 Garage or Room
700 sq ft 31,000-38,000 BTU Up to Two Bedroom Townhouse
1,000 sq ft 45,000-55,000 BTU Up to Three Bedroom Apartment
1,500 sq ft 68,000-82,000 BTU Average Home
2,000 sq ft 90,000-110,000 BTU Guest House
2,500 sq ft 113,000-137,000 BTU Large Home
3,000 sq ft 135,000-165,000 BTU One Zone – Large Home



Together with working out how many BTU per square foot you require, you need to focus on energy efficiency to ensure your bills remain low. In terms of air conditioners, a Seasonal Energy Efficiency Ratio (SEER) rating of over 16 is ideal, while numbers over 15 and 13 are okay. For heat pumps, you must consider the Heating Seasonal Performance Factor (HSPF), where 9.2 and above is appropriate.



Whether you’re replacing or installing a new HVAC system, it’s advisable to speak to a professional technician or company that can perform the necessary calculations and ensure you receive a proper air conditioner which answers the question how many BTU per square foot you require.