CSLB C-20 HVAC ContractorPlanning and LayoutEasy
A single-story home in a California climate zone has identical-sized windows on both the east and west exterior walls. When performing a Manual J cooling load calculation, which orientation typically contributes the greatest solar heat gain load during peak afternoon design conditions?
- AEast-facing windows
- BWest-facing windows
- CNorth-facing windows
- DSouth-facing windows
Show answer & explanationAnswer & explanation
Correct answer: B. West-facing windows
West-facing windows receive direct, low-angle sun during late afternoon hours, which typically coincides with the peak outdoor design temperature used in Manual J cooling calculations, resulting in the highest solar heat gain contribution among common orientations.
Why the other options are wrong
- A. East-facing windows peak in solar gain during morning hours, not at the afternoon design peak.
- C. North-facing windows receive minimal direct solar gain in the Northern Hemisphere.
- D. South-facing windows receive more sun in winter but less intense direct gain at peak summer afternoon hours.
Window Orientation Solar Gain
Solar heat gain through windows varies by orientation and time of day; west-facing glass typically drives peak afternoon cooling loads.
- West windows peak with afternoon sun
- East windows peak in morning
- South gain is highest in winter, moderate in summer at low sun angle
Memory trick: West is worst for afternoon heat.