What causes heat gain in a room?

Heat gain comes from: solar radiation through windows, heat transfer through walls/ceiling, occupants, lighting, and equipment.

How to reduce room heat gain?

Use curtains/blinds, improve insulation, seal air leaks, use energy-efficient lighting, and plant shade trees.

Room Heat Gain Calculator

Understanding Heat Gain

Heat gain analysis helps identify cooling requirements and opportunities for efficiency improvements. By understanding where heat enters your room, you can size your AC appropriately and implement targeted improvements to reduce cooling needs.

Sources of Heat Gain

Heat enters rooms through multiple pathways:

Solar radiation: Sunlight through windows (often the largest source)
Conduction: Heat transfer through walls, roof, and floor
Infiltration: Hot air leaking through gaps and cracks
Internal gains: Heat from people, lights, and equipment

Window Heat Gain

Windows are typically the biggest contributor to heat gain:

Direct solar: 200-300 BTU/sq ft/hour for unshaded glass
Orientation impact: West-facing gets 30-50% more than east
Glass type: Low-E glass reduces gain by 25-40%
Shading: External shades more effective than internal

Wall and Ceiling Heat Transfer

Heat conducts through solid surfaces based on:

Temperature difference: Bigger difference = more heat transfer
R-value: Higher insulation = less heat transfer
Surface area: Larger walls transfer more heat
Color: Dark exterior surfaces absorb more heat

Internal Heat Gains

Heat generated inside the space:

People: 400 BTU (seated), 600 BTU (active), 1,000 BTU (exercising)
Lighting: 3.4 BTU per watt (LED generates less heat)
Computer: 500-1,000 BTU per desktop
TV: 200-400 BTU for large screens
Kitchen: 500-3,000 BTU depending on cooking

Calculating Total Heat Gain

Add all sources for total cooling requirement:

Envelope (walls/ceiling): Area × U-value × temp difference × 3.41
Windows (solar): Area × solar heat gain coefficient × irradiance
Occupants: Number × BTU per person
Equipment: Watts × 3.41 BTU/watt
Infiltration: Volume × air changes × temp diff × 1.08

Reducing Heat Gain

Strategies to minimize cooling load:

External shading: Awnings, trees, overhangs
Window treatments: Reflective film, thermal curtains
Insulation: Add wall and ceiling insulation
Air sealing: Caulk gaps, weatherstrip doors
Roof coating: Reflective white or cool roof coatings
LED lighting: Reduces heat from lights by 80%