Refrigeration BTU Calculator

Measure the box, enter the two temperatures and the panel R-value, and get the heat crossing the panels in BTU/h. Add your own product, door, lighting and motor loads under More detail and it totals them into tons of refrigeration.

Box length

Inside length, wall to wall.

Box width

Inside width, wall to wall.

Box height

Inside height, floor to ceiling panel.

Box measured in

The unit you measured all three sides in. Inside measurements: the panel thickness is insulation, not space.

Inside the box

The temperature the box has to hold. A freezer is a negative number and that is fine.

Around the box

The temperature of the room the box sits in, on the worst day it has to work through. Your figure, not a design table.

Temperature unit

How well the panels block heat (R-value)

R-value says how well the panel stops heat passing through it: the higher the number, the less heat gets in. Read it off the panel spec sheet. Use the inch-pound R-value, not the metric one. The metric figure is called RSI and it is a different number, so do not type that here.

Result

Fill in a few more boxes and the answer will show here.

Opens your print dialog. Choose Save as PDF. Your figures stay on this device.

Loading the calculator.

This is a general measurement calculator. Confirm dimensions, product coverage and job requirements before ordering or installing materials.

How a box load is actually built up

The heat crossing the panels is the one part of a box load that is pure physics. It is the surface area of all six faces, times the temperature difference between the box and the room it sits in, divided by the R-value of the panel. Nothing about the product or the region changes that arithmetic, which is why it is the part this tool does for you.

The temperature difference is where this goes wrong quietly. A temperature and a difference between two temperatures do not convert the same way. Twenty-two degrees Celsius as a temperature is 71.6 °F, because the scale starts 32 degrees higher. A twenty-two degree Celsius spread is only 39.6 Fahrenheit degrees, because a spread has no starting point to shift. Run the spread through the temperature formula and the load comes out close to double, and the answer still looks like a believable BTU figure.

Everything else is yours. The product coming in warm, the door opening forty times an hour, the lights, the evaporator fans. Those depend on what the box does for a living, and no table can tell you. So they start empty, and the result names which ones are missing every time you read it. A panel-only figure quoted as a box load is how a machine ends up running flat out by two in the afternoon.

Take the inside measurements, not the outside: the panel is insulation, not space. Write the box down once against the address, with the panel spec and the two temperatures, and the next call is a service call instead of another survey. Zeus keeps job records per address and works with no signal, which is usually the situation you are in when you are standing in a cooler.

Built for HVAC work: see the HVAC job app.

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