Heat Gain
Heat gain is the rate at which a building takes in thermal energy from its environment in summer, expressed in BTU per hour at design conditions. Heat gain has more components than heat loss: conduction through hot envelope surfaces, infiltration of warm humid air, solar gain through windows (proportional to SHGC), and internal gains from people, lights, and appliances. Sizing cooling equipment requires accounting for both sensible and latent (moisture) heat gain.