# What Size HVAC System Does My Home Require?

Whether it is the first time you’re investing in an HVAC system or searching for a replacement for your existing system, you’d want to purchase one that is ideal for your home. If the system is too small, it’ll have to work harder and use more energy to maintain an ideal temperature. And if you install an oversized unit, you’ll find your home too cold or too hot.

So, how do you select the correct HVAC system size for your home? Well, there are two different methods- approximate calculation and Manual J calculation. Here’s what they mean-

1. HVAC System Approximate Size Calculation Method
As the name suggests, this method will provide you with an approximate size of the HVAC system for your home. Follow these steps to calculate-
• Calculating Square Footage
This is the total floor space of your home. You should be able to find the square footage somewhere in the property documents. If not, you can use a tape measure to find out the exact length and width of every room.
Do this for every room in your home, and then add these values. Finally, add them together to calculate the total square footage of your home.
• Figuring Out the Base BTU
British Thermal Unit or BTU is the unit used for measuring the usage of energy in cooling or heating. You need around 25 BTUs to cool or heat one square foot area. So, multiply the total square footage of your home by 25 to calculate the base BTU
• Accounting for High Ceilings
Higher ceilings also impact the size of the HVAC system you’ll need for your home. If the ceiling is above 8 feet, the base BTU should be multiplied by 25% or 1.25.
• Calculating Approximate HVAC Size
Using the steps listed above, you’ll need 37,500 BTUs for a 1,500 square feet home. For the air conditioning system, divide the total BTU required by 12,000. So, a 1,500 square feet home will need an air conditioning system of around 3 tons.
For furnace size, you’ll only need the total BTU your home requires. So, if you need a 37,500 BTU system, you can buy a 37,000-40,000 BTU furnace.
2. Manual J Calculation Method
The first method discussed above will only provide a basic calculation as it does not consider all the factors critical to selecting the right HVAC size. For instance, it does not account for-
• Total number of people living in the home
• Local climate
• Total windows and doors and their placement
• Type/amount of insulation
• Lighting placement 