Solar Heat Gain Calculator

Advanced calculator estimates window solar gains with configurable precision for professionals. Enter dimensions, SHGC, irradiance, incidence angle, shading, and quantity across multiple windows. Supports metric and imperial units, batch mode, CSV and PDF result downloads. Fast, accurate, white theme, perfect for energy audits today.

Inputs

Select preferred units.
Typical double‑glazed: 0.35–0.70.
0=fully blocked, 1=unshaded.

Windows / Glazed Openings

Name Width Height Area Irradiance Incidence° SHGC Shade Glazing Ratio Qty
Width/Height: m • Area: m² • Irradiance: W/m²
If Area is provided, Width×Height is ignored. Irradiance may be direct estimate or measured value.

Results

Name Area (m²) Eeff (W/m²) SHGC Shade Qty Gain (W) Gain (kW) Gain (BTU/hr)
Total 0 0 0

Formula Used

The instantaneous solar heat gain through glazing is modeled as:

Qsolar = Aglass × Eeff × SHGC × Fshade × N

  • Aglass: effective glazed area (m²). If a frame is present, set the glazing ratio below 1.0.
  • Eeff: effective irradiance (W/m²). We approximate Eeff = E × cos(θ), where θ is the incidence angle from the normal.
  • SHGC: Solar Heat Gain Coefficient of the glass/system (0–1).
  • Fshade: additional shading factor (0–1) for blinds, overhangs, etc.
  • N: number of identical windows.

Output power is shown in Watts, kilowatts, and BTU/hr (1 W = 3.412 BTU/hr). For imperial inputs, irradiance in BTU/hr·ft² is converted using 1 BTU/hr·ft² ≈ 3.1546 W/m².

How to Use This Calculator

  1. Select your Unit System. Hints update automatically for fields.
  2. Click Add Row to enter one or more windows or glazed doors.
  3. Provide either Width & Height or an explicit Area.
  4. Enter Irradiance (W/m² or BTU/hr·ft²), SHGC, Shading, and Incidence Angle.
  5. Use Glazing Ratio to reduce area for frames and dividers.
  6. Adjust default SHGC and shading for rapid row entry.
  7. Review results, then export with Download CSV or Download PDF.

Example Data Table

Name Width Height Area Irradiance Incidence° SHGC Shade Glazing Ratio Qty Unit System Note
South Living 1.5 1.2 700 25 0.55 0.90 0.85 2 Metric Clear midday conditions
West Kitchen 1.1 220 40 0.40 0.80 0.90 1 Imperial Irradiance in BTU/hr·ft²

FAQs

The Solar Heat Gain Coefficient is the fraction of solar radiation admitted through glazing. Typical products range 0.25–0.70; lower values reduce gains, higher values increase passive solar gains.

Radiation striking at an angle is less effective per unit area. We multiply irradiance by cos(θ), where θ is measured from the surface normal (0° is perpendicular).

A multiplier from 0 to 1 representing additional reductions due to blinds, overhangs, films, or nearby obstructions. Use 1 for no extra shading beyond the SHGC rating.

Use on-site measurements, a local weather station, or reliable clear-sky estimates for the chosen surface. Be consistent with units and orientation; adjust incidence angle to approximate orientation effects.

Solar heat gain quantifies radiant energy admitted by glazing. U‑value conduction accounts for thermal flow due to temperature differences. Both impact loads but originate from different mechanisms.

Reference SHGC & Glazing Properties

Typical product ranges for quick assumptions. Use manufacturer data when available.

Glazing Type Typical SHGC Range Visible Transmittance (VT) Notes
Single clear 0.80 – 0.90 0.85 – 0.90 High solar gain, poor insulation.
Double clear 0.65 – 0.80 0.70 – 0.85 Common in mild climates.
Double Low‑E 0.25 – 0.45 0.55 – 0.70 Balanced efficiency for many projects.
Triple Low‑E 0.20 – 0.35 0.45 – 0.65 Lower gain, best insulation.
Spectrally selective 0.25 – 0.40 0.50 – 0.70 Blocks infrared, good daylighting.
Ranges are indicative; verify with product datasheets and certification labels.

Approximate Exterior Irradiance Benchmarks

Use these ballpark figures to seed inputs when local data is unavailable.

Condition / Orientation Irradiance (W/m²) Notes
Clear sky, sun perpendicular 850 – 1000 Near solar noon, minimal clouds.
Clear sky, 30° incidence 700 – 850 Approx. E·cos(θ) reduction.
Partly cloudy 300 – 700 Highly variable with passing clouds.
Overcast daylight 50 – 200 Diffuse sky, no direct beam.
Shaded by overhang/adjacent 50 – 150 Mostly diffuse and reflections.
Low winter sun, clear 300 – 700 Lower altitude reduces beam intensity.
Always prefer site measurements or trusted weather datasets for design decisions.

Notes & Tips

  • Set Incidence Angle to 0° for perpendicular beam conditions.
  • For frames/muntins, reduce Glazing Ratio below 1.0.
  • Interior shades reduce gains; combine SHGC and shading factor.
  • North-facing windows generally experience lower beam gains midday.
  • For hourly profiles, repeat with different irradiance and angles.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.