Heat Load Calculator

Estimate room heat load from area, occupants and equipment. Enter your own values below to see estimated heat load and check the method behind it.

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Your inputs

Change the example values to match your situation.

Your result

Let’s work it out.

Fill in your inputs and select Calculate.
Your result and breakdown will appear here.

How this calculator works

Heat load = area × design heat-load density + occupant heat + equipment heat. 1 refrigeration ton = 12,000 BTU/h.

Before you use the result

  • Preliminary sizing based on entered design factors. Climate, glazing, insulation and ventilation require a full load assessment.

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What is Heat Load Calculator?

Heat Load Calculator helps you estimate room heat load from area, occupants and equipment.

The main result is estimated heat load, with a breakdown of cooling load. The formula, example and assumptions below explain how to interpret it.

How to use Heat Load Calculator

Use the example to get familiar with the form, then enter your own figures. Any rates in the example are illustrative. Check the field labels and units before calculating.

  1. Gather room floor area (ft²), design heat load per square foot (BTU/h/ft²), occupants, heat per occupant (BTU/h) and equipment heat load (W). Use values from the same situation or reporting period.
  2. Replace the example room floor area with your own value, then complete the other fields. Check the displayed units.
  3. Select Calculate and read estimated heat load with its result breakdown. Change one input and calculate again to compare a second scenario. Reset restores the original example.
  • Enter room floor area in ft², at least 0. Decimals are accepted.
  • Enter design heat load per square foot in BTU/h/ft², at least 0. Decimals are accepted.
  • Enter occupants, at least 0 and at most 1000. Use a whole number.
  • Enter heat per occupant in BTU/h, at least 0. Decimals are accepted.
  • Enter equipment heat load in W, at least 0. Decimals are accepted.

Heat Load Calculator: a worked example

With the inputs below, the result is 9,612.141633 BTU/h (estimated heat load). Follow the example, then replace these illustrative values with your own.

Example inputs and output
Input or outputExample value
Room floor area (ft²)200 ft²
Design heat load per square foot (BTU/h/ft²)25 BTU/h/ft²
Occupants2
Heat per occupant (BTU/h)600 BTU/h
Equipment heat load (W)1,000 W
Estimated heat load9,612.141633 BTU/h
Cooling load2.817041 kW

Understanding the Heat Load result

Read estimated heat load alongside cooling load. These describe different parts of the same calculation.

Displayed results use a readable number of decimal places. When checking a result by hand, keep extra precision until the last step. To compare scenarios, change one input at a time and keep the others fixed.

  • Example Cooling load: 2.817041 kW

Heat Load Calculator: assumptions and common mistakes

A useful estimate starts with the right inputs. Check the following assumptions and limits before applying the result to your situation.

  • Preliminary sizing based on entered design factors. Climate, glazing, insulation and ventilation require a full load assessment.
  • DC, single-phase and three-phase calculations use different relationships. Equipment selection also depends on installation conditions and applicable standards.

For wider guidance, visit Bureau of Indian Standards. The formula and scope of this specific tool are stated on this page.

Heat Load Calculator FAQs

What does Heat Load Calculator calculate?

Heat Load Calculator helps you estimate room heat load from area, occupants and equipment. Its main output is estimated heat load in BTU/h.

What inputs do I need for Heat Load Calculator?

You need room floor area (ft²), design heat load per square foot (BTU/h/ft²), occupants, heat per occupant (BTU/h) and equipment heat load (W). Use the field labels and units to match your figures to the formula.

Which formula does Heat Load Calculator use?

Heat load = area × design heat-load density + occupant heat + equipment heat. 1 refrigeration ton = 12,000 BTU/h.

What is a worked example for Heat Load Calculator?

Example inputs: Room floor area: 200 ft²; Design heat load per square foot: 25 BTU/h/ft²; Occupants: 2; Heat per occupant: 600 BTU/h. Keep the remaining inputs as shown in the worked-example table. The result is 9,612.141633 BTU/h (estimated heat load).

How should I enter room floor area?

Enter room floor area in ft², at least 0. Decimals are accepted.

How do I choose design heat load per square foot?

Enter design heat load per square foot in BTU/h/ft², at least 0. Decimals are accepted. The example uses 25 BTU/h/ft²; replace it if your circumstances differ.

How should I read estimated heat load?

Read estimated heat load alongside cooling load. These describe different parts of the same calculation.

Why might my Heat Load Calculator result differ from my records?

Preliminary sizing based on entered design factors. Climate, glazing, insulation and ventilation require a full load assessment. Differences in entered values, units or rounding can also change the comparison.

Can I compare two scenarios in Heat Load Calculator?

Yes. Note your first estimated heat load, change room floor area or another input, and select Calculate again. Editing a field clears the old result so it is not mistaken for a new calculation.

Is Heat Load Calculator free, and where are my inputs calculated?

This calculator is free to use without signing in. Its formula runs in your browser; calculator inputs are not sent to a calculation API. The inputs reset to the example values when you reset the form or start a fresh page.