Garage Heater Calculator

Garage Heater BTU Calculator

Calculate the exact heating capacity needed for your workspace

Excellent (Fully Insulated) Average (Walls/Doors insulated) Poor (Minimal insulation) None (Metal/Wood shed style)

Calculation Results

0 BTUs

Total Volume: 0 Cubic Feet

Recommended Heater Size: 0 kW (Electric equivalent)

How to Size a Garage Heater Correctly

Choosing the right garage heater is critical for maintaining a comfortable working environment during winter. If you undersize the unit, the heater will run constantly without ever reaching your desired temperature. If you oversize it, you waste energy and deal with rapid cycling that can wear out components.

The Physics of Heating Your Garage

Unlike rooms inside your home, garages often have high ceilings, concrete floors that act as heat sinks, and large overhead doors that leak air. Our calculator uses the Volume-Based BTU Formula, which is the most accurate method for workshops and garages:

  • Volume: We calculate total cubic feet (L x W x H) because hot air rises, making ceiling height a major factor.
  • Temperature Rise: The difference between your target temperature (e.g., 60°F for working) and the coldest winter temperature in your region.
  • Insulation Coefficient: This represents how quickly heat escapes. A metal shed without insulation requires significantly more energy than a finished garage with R-19 walls.

Example Calculation

Imagine a standard 2-car garage: 20ft wide, 20ft long, and 10ft high. That's 4,000 cubic feet. If it's 20°F outside and you want it 65°F inside, your rise is 45°F. With average insulation (factor 0.15), the math is: 4,000 × 45 × 0.15 = 27,000 BTUs.

Quick Tips for Efficiency

  • Insulate the Door: Garage doors are usually the biggest source of heat loss. An insulation kit can reduce your BTU requirements by up to 20%.
  • Ceiling Fans: Since heat rises, use a ceiling fan on low speed in reverse to push warm air back down to the floor.
  • Thermostat Placement: Avoid placing thermostats near the heater itself or the garage door to prevent false readings.
function calculateGarageBTU() { var length = parseFloat(document.getElementById("garageLength").value); var width = parseFloat(document.getElementById("garageWidth").value); var height = parseFloat(document.getElementById("garageHeight").value); var target = parseFloat(document.getElementById("targetTemp").value); var outside = parseFloat(document.getElementById("outsideTemp").value); var factor = parseFloat(document.getElementById("insulationFactor").value); // Validation if (!length || !width || !height || isNaN(target) || isNaN(outside)) { alert("Please enter all required dimensions and temperatures."); return; } // Step 1: Calculate Volume var volume = length * width * height; // Step 2: Calculate Temp Rise var tempRise = target – outside; if (tempRise <= 0) { tempRise = 1; // Minimum rise for logic } // Step 3: Calculate BTU // Formula: BTU = Volume * TempRise * Insulation Factor // A standard multiplier for average garage is roughly 0.133-0.15 per cubic foot per degree rise var totalBTU = Math.ceil(volume * tempRise * factor); // Step 4: Convert to kW (1 kW = ~3412 BTU) var totalKW = (totalBTU / 3412).toFixed(1); // Display Results document.getElementById("btuResult").innerHTML = totalBTU.toLocaleString(); document.getElementById("volumeResult").innerHTML = volume.toLocaleString(); document.getElementById("kwResult").innerHTML = totalKW; document.getElementById("resultArea").style.display = "block"; // Smooth scroll to result document.getElementById("resultArea").scrollIntoView({ behavior: 'smooth', block: 'nearest' }); }

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