Calculator inputs
Use the responsive input grid below. It shows three columns on large screens, two on smaller screens, and one on mobile.
Formula used
Gross Opening Area = Width × Height × Quantity
Net Glass Area = Gross Opening Area × Glass Fraction
Effective Irradiance = Solar Irradiance × Orientation Factor × Exterior Shading Factor × Interior Shading Factor
Instant Solar Gain = Net Glass Area × SHGC × Effective Irradiance
Adjusted Solar Gain = Instant Solar Gain × Cooling Load Factor
Daily Heat Gain = Adjusted Solar Gain × Exposure Hours ÷ 1000
Cooling Tons = Adjusted Solar Gain × 3.412142 ÷ 12000
If you enter dimensions in feet, the calculator converts them to meters before applying the heat gain equations. One foot equals 0.3048 meters.
How to use this calculator
- Choose metric or imperial units first so your width and height labels match your project drawings.
- Enter window width, height, quantity, and the approximate glass fraction for the assembly.
- Input the glazing SHGC and the design solar irradiance from your climate, facade study, or manufacturer data.
- Select an orientation preset or enter a custom factor for a more detailed facade adjustment.
- Add exterior shading, interior shading, and cooling load factor values that reflect the design condition.
- Enter daily exposure hours, equipment COP, and electricity rate for operational estimates.
- Press the calculate button. The result, chart, and export buttons will appear above the form.
Example data table
| Opening | Gross Area (m²) | SHGC | Irradiance (W/m²) | Combined Shade Factor | Adjusted Gain (W) |
|---|---|---|---|---|---|
| West Office Window Bank | 16.20 | 0.38 | 650 | 0.72 | 2,519 |
| South Lobby Curtain Wall | 24.00 | 0.30 | 700 | 0.60 | 2,858 |
| North Classroom Windows | 10.80 | 0.40 | 480 | 0.85 | 1,282 |
| Skylight Array | 8.50 | 0.45 | 820 | 0.65 | 2,216 |
These rows are illustrative examples for comparison only. Replace them with project-specific dimensions, glass data, and solar assumptions.
FAQs
1) What is solar heat gain in buildings?
Solar heat gain is the sun-driven heat entering through glazing and related components. It depends on area, SHGC, orientation, irradiance, and shading. Higher gain can increase indoor temperature, cooling demand, and occupant discomfort.
2) What does SHGC mean?
SHGC means Solar Heat Gain Coefficient. It shows how much solar radiation passes through the glazing assembly as heat. Lower SHGC values usually reduce cooling loads in hot or mixed climates.
3) Why does orientation matter?
Orientation changes how much direct sun strikes the opening. West and skylight exposures often experience stronger peak gains, while north-facing openings usually receive less direct solar intensity during design periods.
4) Do exterior shades help more than interior shades?
Often yes. Exterior shading can block solar radiation before it reaches the glass, which is usually more effective than stopping heat after it enters the glazing system. Combining both can improve performance further.
5) Is this calculator suitable for HVAC sizing?
It is useful for early-stage estimating, comparisons, and concept design. Final HVAC sizing should still use a full load calculation method, project-specific weather data, schedules, and complete envelope details.
6) What is the cooling load factor?
Cooling load factor adjusts instantaneous heat gain to better reflect how that heat becomes a cooling load over time. It is commonly used in simplified design methods and preliminary engineering studies.
7) Why estimate AC energy and daily cost?
Those values help connect envelope choices to operating impact. By using daily heat gain, equipment COP, and electricity rate, you can compare how glazing and shading options may affect cooling energy use.
8) Can I use this for skylights?
Yes. Skylights usually see higher solar exposure, so the skylight orientation preset uses a stronger factor. You can also switch to a custom factor if your design team has better simulation or climate data.