How to mitigate heat transfer for better building efficiency

The Energy Drain of Buildings

Buildings use 75% of all the electricity consumed in the U.S. each year, with residential buildings alone consuming more than 33%. Energy efficiency is not only the most cost-effective way to meet the growing power demands, it is a crucial factor in keeping energy costs lower for everyone. A key contributor to high electricity bills is the amount of energy used to maintain a comfortable indoor environment, which can be significantly impacted by different forms of heat transfer.

Understanding Heat Transfer

Heat transfer in buildings occurs in three primary ways: conduction, convection, and radiation. Below are practical tips for how to reduce heat transfer and examples for each type to help inform your building practices.

Conduction

Conductive heat transfer occurs when heat moves through adjacent materials, such as walls, floors, and ceilings.

Examples:

• Heat loss through poorly insulated walls and roofs.
• Cold floors due to heat escaping through the ground or uninsulated floors.
• Thermal bridging due to pathways within the building’s envelope.

Tips to Mitigate:

• Use advanced insulation materials and approaches: Exterior rigid foam and blown-in blanket insulation can provide better thermal resistance than traditional fiberglass batts.
• Use insulated concrete forms: These provide superior thermal insulation and can also improve the structural integrity of the building.
• Eliminate thermal bridges: Use structural thermal breaks, such as thermally broken window frames and insulating spacers in walls, to prevent heat from escaping through structural elements.
• Add or improve floor insulation: Use insulated underlayment under floors to prevent heat loss to the ground.

Convection

Convective heat transfer involves the movement of heat through liquids or gasses, but more typically in buildings, convection occurs through air.

Examples:

• Forced-air heating and cooling systems moving heat through the ductwork.
• Warm air leaking from the ductwork or building enclosure through gaps in the ducting or air barrier.
• Spot ventilation, such as a kitchen stove vent or bathroom fan, unintentionally removing heat and vapor.
• Opening upstairs or second-story windows to use the stack effect for cooling the home, also known as night flushing.

Tips to Mitigate:

• Implement effective air sealing: Use an effective air sealing checklist that includes sealing all building penetrations, framing material connections, and top plates to ventilated attics, before insulating exterior walls. Evaluate the effectiveness of your approach with a blower door, then improve future projects accordingly.
• Improve duct sealing: Apply nickel-thick mastic to seal duct joints and connections and prevent air leaks.
• Use heat recovery ventilators and energy recovery ventilators: These systems recover heat from exhausted air to pre-warm incoming air, significantly reducing heating and cooling loads.
• Install smart thermostats and HVAC systems: Smart systems can adjust airflow dynamically based on occupancy and real-time temperature readings, which can help optimize heating and cooling efficiency.
• Balance ventilation systems: Ensure the ventilation system is balanced to maintain neutral pressure, and reduce the risk of air infiltration and exfiltration.

Radiation

Radiation transfers thermal energy through electromagnetic waves. Mitigation strategies help moderate the interior surface temperature of a building to improve comfort.

Examples:

• Heat gain through windows from direct sunlight.
• Heat transfer from people’s bodies.
• Heat loss from the building envelope during the night.

Tips to Mitigate:

• Install energy-efficient windows: Use double- or triple-pane windows with low-emissivity (Low-E) coatings to reduce heat gain and loss. This is achieved by moderating the surface temperature inside so occupants radiate less heat to those surfaces, increasing comfort.
• Use reflective roofing materials: Materials that reflect more sunlight (e.g., lighter-colored shingles) help reduce heat absorption and keep the building cooler in the summer.
• Incorporate passive solar design: Position windows, walls, and floors to collect, store, and distribute solar energy as heat in the winter—and reject solar heat in the summer.
• Use window treatments: Blinds, shades, or films can help control the amount of solar radiation entering the home.
• Design overhangs and awnings: Use these features to help shade windows from direct sunlight in the summer while allowing solar gain in the winter.
• Properly insulate walls: Ensure wall insulation meets adequate R-values for your climate and is properly installed, avoiding gaps, voids, and compression. This helps occupants feel warmer, so the air temperature inside doesn't have to be as high to be comfortable.

Dive Deeper into Energy Efficiency

Eager to learn about implementing these energy-efficiency strategies and applying them to your projects? Visit our on-demand trainings that cover the "what," "why," and "how" of practical installation techniques and approaches to ensure your projects meet high standards of energy efficiency.

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