Heat Loss Calculator (BTU)
Heat loss through a surface is area divided by R-value, times the temperature difference. Enter your assembly to see the BTU per hour and what it costs you each year.
Your project
Your results
- Heat loss now
- 4,154 BTU/hr
- Heat loss after upgrade
- 1,102 BTU/hr
- Reduction
- 73%
- Annual fuel now
- 161 therms — $233
- Annual fuel after
- 43 therms — $62
- Annual saving
- $171
Estimates use typical US material and labor pricing. Confirm quantities against the coverage chart on the bag before you buy.
Gear for this job
Thermal Imaging Camera Home Inspection
TOPDON TC004 Mini Thermal Imaging Camera, 240 x 240 TISR Resolution | 15H Battery Life, 25Hz Handheld Infrared Camera with High/Low Temp Alerts, Auto Shutdown, 128 x 128 IR Resolution, Blue
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TOPDON TC004 3.5" Thermal Imaging Camera, -4°F~1022°F Temp Range | 512 x 384 TISR Resolution, 8-Hour Battery Life Handheld Infrared Camera with PC Analysis and Video Recording, 64GB Storage
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Thermal Master Thor002 Handheld Thermal Camera, 512 × 384 X³ Resolution | 3.5" IPS Screen, 5 Imaging Modes, -4℉ to 1022℉, ±3.6℉ Accuracy Thermal Imaging Camera for Home, HVAC, Electrical Inspections
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Infrared Thermometer Gun
Etekcity Infrared Thermometer Laser Temperature Gun 774 | Cooking, Pizza Oven, Griddle, BBQ, Meat, HVAC, Engine, Adjustable Emissivity, MAX Display, Surface Measurement
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TempPro TempScan Infrared Thermometer Gun for Pizza Oven Griddle HVAC | Temperature Gun with Adjustable Emissivity, Infrared Thermometer for Cooking BBQ Meat Engine, Temp Gun with -58~1022°F
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Digital Infrared Thermometer gun for cooking,BBQ,Pizza oven,Ir Thermometer with Backlight,-58℉~932℉(-50℃~500℃) Handheld Non Contact Heat Laser Temperature Gun (Not for Human)
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Thermal Leak Detector Infrared
BLACK+DECKER Thermal Leak Detector (TLD100)
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Flir One - Thermal Imaging Camera for iOS Smartphones (iPhone 14 and Older w/Lightning Port), 240x180 Super Resolution (80x60 Native IR)
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Elitech HVAC Refrigerant Leak Detector 10 Yrs Infrared Sensor Life, Halogen Freon Sniffer, Air Conditioning Detection, Automotive Gas Finder, ILD-200
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How this calculator works
- Heat loss (BTU/hr) = area × temperature difference ÷ R-value
- Annual load ≈ area × heating degree days × 24 ÷ R ÷ 100,000
- Saving = fuel before − fuel after, at your energy price
Frequently asked questions
Why does doubling R-value not halve my bill?
Because the attic is only part of the envelope. Going R-13 to R-49 cuts that surface's loss by about 73%, but walls, windows, doors and air leakage keep on losing heat.
What temperature difference should I use?
Design conditions: your indoor set point minus the coldest typical outdoor temperature. Forty to sixty degrees is a realistic range for most of the US.
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Heat loss now
4,154 BTU/hr