HVAC Load Calculator. Simple Manual J Calculation

BTU Calculator

Cooling Load:


Manual J Calculation

If you want to properly size an HVAC unit for a residential building, you should use the technique designed by the ACCA Association (Air Conditioning Contractors of America), the Manual J Residential Calculation.

What is Manual J?

According to ACCA, the “Manual J 8th Edition is the national ANSI-recognized standard for producing HVAC equipment sizing loads for single-family detached homes, small multi-unit structures, condominiums, townhouses, and manufactured homes.”

In short, Manual J is the protocol that is used in order to determine the correct amount of heat that is needed to keep a house warm for its occupants, and the amount of cold air required in order to cool it when needed.

The Manual J Calculation gets complicated oftentimes and requires good knowledge of the technique. This is why contractors developed rule of thumb methods like the simple BTU calculator which you can use above.

If you want to do a proper size of your equipment and want to make precise calculations in order to determine the HVAC load of a residential building, we recommend this free HVAC Load Calculator

HVAC Load Calculator

There are many other online Load Calculators that you can use for free.

The above HVAC calculator is a simple version of those, helping you easily get a sense of the correct size of the equipment that needs to be installed.

In order to determine the correct size of your equipment you need to divide the total cooling load that you obtained above to 12,000 (12,000 BTU make 1 ton).

How to calculate HVAC load

In order to calculate the HVAC load that you need for a residential building, you should keep in mind that there are a few common factors that need to be considered:

1 occupant = 100 additional BTU
1 window = 1000 additional BTU
1 exterior door =1000 additional BTU

For the HVAC calculations above we used this simple formula:

Let’s say that we want to determine the HVAC load for a residential building that has 1000 square feet, 8 ft tall ceiling, 5 windows, and 2 exterior doors, that is occupied by 3 people.

The HVAC load calculations would look like this:

1000 sqft (house surface) x 8 ft (hight of the ceiling) = 8000

3 (occupants) x 100 = 300

5 (windows) x 1000 = 5000

2 (exterior doors) x 1000 = 2000

Total HVAC load = 15,300 BTU

Knowing that for every 12,000 BTU you should add 1 ton to the HVAC equipment, the correct equipment size for this particular house would be 1.5 ton.


The above formulas and calculations are estimated in good faith and are intended for generic, informative purposes. We do not guarantee the accuracy of this information. There are also other external factors that may affect or falsify the recommended BTUs. For accurate values, please consult a licensed HVAC company or engineer.

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