The energy efficiency of double-hung windows and casement windows can vary depending on several factors, including the quality of the window, the materials used, and the design. Here are some factors to consider:

Air Leakage: Casement windows typically have lower air leakage rates than double-hung windows, as they are designed to seal tightly when closed. However, this may not be the case if the windows are poorly designed or installed.

Ventilation: Both types of windows can provide ventilation, but casement windows tend to allow more airflow when open.

Insulation: Double-hung windows tend to provide better insulation than casement windows, as they have two sashes that can trap air between them, helping to reduce heat transfer. However, this also depends on the quality of the windows and materials used.

Maintenance: Casement windows tend to be easier to maintain, as they have fewer moving parts that can break or wear down over time.

Overall, it’s difficult to say whether double-hung windows are more efficient than casement windows, as it depends on a variety of factors. However, both types of windows can be energy-efficient if they are of high quality, properly installed, and well-maintained. It’s important to consider your specific needs and situation when choosing between double-hung and casement windows, and to consult with a professional window contractor to determine the best option for your home.