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How to Determine the Size of HVAC You Need

May 29, 2015

How to Determine the Size of HVAC You Need

When looking to install a new HVAC system in your home, it is important to make sure it is sized correctly. If it is too small, it might not be able to regulate the temperature of your whole home. On the other hand, an oversized unit will not work as efficiently, may wear out faster, and possibly have dehumidification problems. The process involved in determining the right size air conditioner and furnace for your home is a very complicated process, but it is possible to do a general estimate on your own.

Approximate Calculations

To determine the approximate size of your HVAC system, use the following calculations:

  • First, determine square footage: Find out the floor space in your home. You might be able to find the number written down somewhere, or you might have to measure it yourself. To measure a room on your own, use a tape measure to determine the length and width. Multiply those together for the square footage for that room. Repeat the process for each room and hallway, then add them all together.
  • Second, determine the base BTU: The unit used to measure energy used for heating and cooling is the British Thermal Unit, or BTU. The approximate amount of energy used to cool a square foot of your home is roughly 25 BTUs, so multiply the number of square feet in your home by 25 to get the base BTU measurement.
  • Third, account for high ceilings: If your home’s ceiling is over 8 feet, multiply the base BTU amount by 1.25, or 25%.

For a 1500 square foot home with normal ceilings, the result would be about 37,500 BTUs. Once you have the base BTUs figured for your home’s size, you can then figure out the size of AC and heating units you need. For the air conditioner, divide the number by 12,000 to determine the tonnage required. For the furnace, divide the BTU by the unit’s efficiency as a decimal.

In the case of a 1500 sq. ft. home, the air conditioner would need to be 37,500 ÷ 12,000, which comes out to about 3 tons. For the furnace, an 80% efficiency unit would need a BTU output of about 37,500 × 0.8, which is about 47,000 BTU.

Manual J: The Professional Method

Of course, these are very basic calculations, and they do not take into account the number of people in the building, the climate of the area, the number and placement of windows, whether those windows face north or south, the amount/type of insulation in the walls, lighting placement, and multiple other factors.

For more precise measurements, professionals will use the Manual J calculations, which take all of these factors into account. This allows the technician to know exactly what size HVAC to install in your home for optimum comfort and efficiency. A properly trained HVAC professional will be able to make the proper measurements and design a system that meets your home’s climate control needs. At Climate Tech Air Conditioning and Heating, we provide the needed expertise to make sure your home’s temperature is well regulated year round. To get an estimate for your home, give us a call today.

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