Window Heat Gain Calculator
Solar + conduction gain through glazing from SHGC, U-value and incident solar.
Solar dwarfs conduction: 4 m² of SHGC-0.6 glass in evening sun gains 1.2 kW — a third of a ton of AC for one window. Films and shading fix SHGC cheaply.
Formula
Window Heat Gain Calculator is a free window heat gain for HVAC designers, technicians and energy auditors — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Window Heat Gain Calculator
Solar + conduction gain through glazing from SHGC, U-value and incident solar. The calculation implements Q = A·SHGC·I + A·U·ΔT (NFRC ratings; ASHRAE fenestration chapter). Solar dwarfs conduction: 4 m² of SHGC-0.6 glass in evening sun gains 1.2 kW — a third of a ton of AC for one window. Films and shading fix SHGC cheaply.
How to use Window Heat Gain Calculator
- 1Enter Glass area in m².
- 2Enter SHGC (Single clear 0.82 · double 0.70 · low-E solar 0.25).
- 3Enter Incident solar irradiance in W/m² (West glass on a summer evening: 500–700).
- 4Enter Glass U-value in W/m²K.
- 5Read Total gain, Solar share instantly — no submit button needed.
- 6Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Window Heat Gain Calculator?
- ✓Implements the standard formula — Q = A·SHGC·I + A·U·ΔT
- ✓Reference cited on-page: NFRC ratings; ASHRAE fenestration chapter
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Window Heat Gain Calculator use?+
It computes Q = A·SHGC·I + A·U·ΔT, per NFRC ratings; ASHRAE fenestration chapter. The formula is displayed under the result.
What should I keep in mind when using this calculator?+
Solar dwarfs conduction: 4 m² of SHGC-0.6 glass in evening sun gains 1.2 kW — a third of a ton of AC for one window. Films and shading fix SHGC cheaply.
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the Window Heat Gain Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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