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Overhead Door Infiltration Loss Calculator - Quantify Heat Lost Through Shop Doors

Calculate BTU loss from air leakage around closed doors and cold air dumped during door openings

Free overhead door infiltration calculator for shops, garages, fire stations, and loading docks. Overhead doors are the single largest source of heat loss in most outbuildings, but most heater sizing guides ignore them or use a generic "add 20%" rule that can be wildly wrong. This calculator breaks infiltration into two distinct components: perimeter leakage around a closed door based on seal condition and wind pressure, and full-volume air exchange during open cycles based on how many times per hour the door opens and how long it stays open. Enter door dimensions, seal condition, opening frequency, wind exposure, and indoor/outdoor temperature difference to get BTU/hour loss for each component. The tool also estimates annual fuel cost attributable to each door so you can calculate the payback on better weatherstripping, air curtains, or strip curtain installations. For shops with multiple overhead doors, run the calculation for each door separately since seal condition and usage patterns usually differ.

Pro Tip: A 10×10 overhead door opened for 3 minutes dumps roughly 3,000 cubic feet of cold air into your shop - that's the entire volume of a 10×10×10 bay. In a 0°F climate with a 60°F shop, that single opening costs about 3,500 BTU to recover. Open it 10 times a day and you're burning 35,000 BTU/day just on door openings - before any perimeter leakage. A $300 strip curtain behind a frequently-used door often pays for itself in a single heating season.

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Overhead Door Infiltration Loss Calculator
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How It Works

  1. Enter Door Dimensions

    Input door width and height. Standard residential overhead doors are 8×7, 9×7, or 16×7. Commercial and shop doors commonly run 10×10, 12×12, or 14×14. The calculator uses these to compute both perimeter length and open area.

  2. Rate Your Door Seal Condition

    Select from new/tight, good, fair, poor, or no seals. This sets the infiltration rate per linear foot of perimeter. A door with worn bottom seals and gaps at the side tracks can leak 3-5 times as much air as a door with intact seals.

  3. Set Opening Frequency and Duration

    Enter how many times per day the door opens fully and the average duration of each opening. A busy service shop might open 20+ times per day; a storage building might open twice a week.

  4. Enter Temperature and Wind Conditions

    Input indoor target temperature, outdoor design temperature, and wind exposure level. Wind-driven infiltration can triple perimeter leakage compared to calm conditions.

  5. Review Loss Breakdown and Savings Opportunities

    See BTU/hour loss from perimeter leakage and door openings separately, plus annual fuel cost. The calculator shows the estimated savings from sealing improvements, air curtains, and strip curtains so you can evaluate payback.

Built For

  • Shop owners diagnosing why their heater can't maintain temperature on windy days
  • Fire departments calculating heat loss through apparatus bay doors
  • Warehouse managers evaluating air curtain or strip curtain ROI
  • HVAC contractors sizing replacement heaters for buildings with large doors
  • Building owners comparing the cost of insulated vs. non-insulated overhead doors

Frequently Asked Questions

Heat loss through an overhead door comes from two paths: conduction through the door panel (typically 500-2,000 BTU/hr for a 10×10 door at 60°F delta-T) and infiltration around and under the door (1,000-5,000 BTU/hr depending on seal condition and wind). Each full opening adds 2,000-5,000 BTU for a 10×10 door. In a busy shop, infiltration from openings usually exceeds all other losses combined.
Yes, a properly installed air curtain rated for the door size can reduce cold air infiltration during openings by 60-80%. They create a wall of high-velocity air across the doorway that separates indoor and outdoor air. The ROI depends on opening frequency - for a door that opens 10+ times per day in a cold climate, a $1,500-3,000 air curtain often pays back within 1-2 heating seasons.
Insulated doors reduce conduction loss by 60-75% but don't help with infiltration around seals or air exchange during openings. In a shop where the doors stay closed most of the time, insulated doors are worth the upgrade. In a high-traffic shop with frequent openings, the conduction savings are dwarfed by infiltration losses - spend the money on good seals and strip curtains first.
In order of cost-effectiveness: (1) Replace worn bottom and side seals ($50-150 per door). (2) Install strip curtains behind frequently-used doors ($200-500). (3) Add weather stops at the header and jambs ($30-80). (4) Upgrade to insulated door panels if your current doors are single-skin metal ($800-2,500). (5) Install a heated air curtain for high-traffic commercial doors ($1,500-5,000).
Disclaimer: This calculator provides estimates based on standard infiltration rates and engineering assumptions. Actual infiltration depends on door type, installation quality, building pressurization, and local wind conditions. Results are intended for planning and comparison, not for engineering design. Consult an HVAC professional for critical applications.

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