Radiant Tube Heater Sizing Calculator

Radiant Tube Heater Sizing Calculator

Calculation Results

Total Area: sq. ft.

Recommended Heating Capacity: BTU/hr

Recommended Minimum Mounting Height: ft.

System Recommendation:

function calculateRadiantHeat() { var length = parseFloat(document.getElementById('roomLength').value); var width = parseFloat(document.getElementById('roomWidth').value); var height = parseFloat(document.getElementById('ceilingHeight').value); var insulation = document.getElementById('insulationQuality').value; if (isNaN(length) || isNaN(width) || isNaN(height) || length <= 0 || width <= 0 || height 12) { heightMultiplier = 1 + ((height – 12) * 0.02); } var totalBTU = Math.round(area * baseBTUFactor * heightMultiplier); // Mounting height safety check var minMounting = Math.round(height * 0.8); if (minMounting < 10) minMounting = 10; // Suggested Tube Lengths var rec = ""; if (totalBTU < 50000) { rec = "A single 20ft or 30ft radiant tube (40k – 50k BTU) should be sufficient."; } else if (totalBTU < 100000) { rec = "Consider one 40ft or 50ft tube heater (75k – 100k BTU)."; } else if (totalBTU < 150000) { rec = "A 50ft or 60ft high-output unit, or two smaller units for better heat distribution."; } else { var units = Math.ceil(totalBTU / 100000); rec = "Large space detected. Multiple units recommended (" + units + " units of 100k+ BTU each) to ensure uniform floor coverage."; } document.getElementById('calcArea').innerText = area.toLocaleString(); document.getElementById('calcBTU').innerText = totalBTU.toLocaleString(); document.getElementById('calcMounting').innerText = minMounting; document.getElementById('systemRec').innerText = rec; document.getElementById('heaterResults').style.display = 'block'; }

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How to Size a Radiant Tube Heater

Sizing a radiant tube heater for your garage, workshop, or warehouse is fundamentally different than sizing a forced-air furnace. Radiant heaters work by emitting infrared waves that heat objects (the floor, tools, and people) rather than just heating the air. This makes them significantly more efficient for high-ceiling environments and drafty spaces.

Key Factors in the Calculation

• Square Footage: The primary driver of BTU requirements. Larger areas require more energy to maintain floor temperature.
• Insulation Quality: A metal building with no insulation loses heat rapidly through the skin, requiring up to 50 BTUs per square foot. A well-insulated modern shop may only require 20-25 BTUs per square foot.
• Ceiling Height: Radiant tubes must be mounted high enough to allow the heat pattern to spread effectively, but not so high that the infrared energy dissipates. Generally, the higher the mounting, the higher the BTU output required to maintain intensity at the floor level.
• Delta T: The difference between the coldest outdoor temperature and your desired indoor temperature.

Sizing Example

Imagine a standard 30′ x 40′ detached garage (1,200 sq. ft.) with average insulation and 12-foot ceilings:

1. Area: 1,200 sq. ft.
2. Base Requirement: 1,200 sq. ft. × 35 BTU (Average insulation) = 42,000 BTUs.
3. Height Adjustment: At 12 feet, no major adjustment is needed.
4. Result: A 45,000 to 50,000 BTU unit with a 20-foot or 30-foot tube would be ideal.

Why Tube Length Matters

The length of the tube affects the "heat throw." A shorter tube concentrates heat in a smaller area, which can create "hot spots." A longer tube spreads those same BTUs over a larger surface area, providing more uniform comfort. For most residential garages, a 20ft to 40ft tube is standard, while industrial applications often use 50ft to 80ft configurations.

Mounting Safety and Clearances

When installing your sized heater, always consult the manufacturer's manual for "Clearance to Combustibles." Radiant heaters get extremely hot. You must ensure that vehicles, storage shelves, and garage doors do not come within the specified safety zone (typically 3-5 feet from the sides and bottom of the tube).