A benefit of lower window U-factor is:

The U-factor (or U-value) measures the rate of non-solar heat transfer through a window assembly. A lower U-factor indicates a slower rate of heat flow, meaning the window has better insulating properties. This superior insulation reduces heat loss during the winter and heat gain during the summer. As a result, the building's heating, ventilation, and air conditioning (HVAC) system does not need to work as hard to maintain a comfortable indoor temperature, leading directly to reduced energy consumption and lower utility bills.

A. Increased visibility is primarily determined by a window's Visible Transmittance (VT), not its U-factor.
C. Increased daylighting is a function of Visible Transmittance (VT), which measures the amount of visible light passing through the glass.
D. Reduced maintenance is related to the durability of window frame materials and hardware, not the window's thermal performance (U-factor).

1. U.S. Green Building Council. (2021). LEED v4.1 Homes and Multifamily Reference Guide. Washington, DC: U.S. Green Building Council. The guide's Energy & Atmosphere (EA) Prerequisite: Minimum Energy Performance section relies on ENERGY STAR standards, which set maximum U-factor requirements for fenestration specifically to ensure a baseline level of energy efficiency (p. 168-170).

2. U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy. (n.d.). Energy Performance Ratings for Windows, Doors, and Skylights. Retrieved from energy.gov. The document states, "U-factor is the rate at which a window, door, or skylight conducts non-solar heat flow... The lower the U-factor, the more energy-efficient the window, door, or skylight." This directly links a lower U-factor to energy savings.

3. National Fenestration Rating Council. (2020). NFRC 100-2020: Procedure for Determining Fenestration Product U-factors. The existence and purpose of this standard are to provide a uniform method for evaluating the heat transfer characteristic of fenestration, which is a critical component in calculating building energy loads. The entire rating system is predicated on informing consumers about energy performance.