How to Pass the Thermal Envelope Test:

Purpose of the Thermal Envelope Test
This test limits the infiltration of outdoor air into the home, especially during wind events. The primary focus is sealing penetrations in the drywall and reducing air leaks in exhaust systems.

Steps to Improve the Thermal Envelope

1. Seal Drywall Penetrations

  • Outlets: Remove outlet cover plates and seal gaps around wires inside the junction box with an approved sealant.

  • Smoke Detectors: Seal drywall penetrations behind smoke detectors using putty or expansive sealant.

  • Thermostats: Seal control wire penetrations behind thermostats with putty, foam, or grommets.

  • Plumbing Penetrations: Seal gaps where plumbing lines pass through drywall, especially under sinks, near water heaters, and other penetrations.

  • Recessed Lights: Verify gaskets are installed around the recessed lights. Verify that the drywall penetration is minimized to its fullest extent.

2. Weather Stripping

  • Attic Access: Apply weather stripping to the attic access lid or its frame to reduce airflow.

  • Exterior Doors: Seal all exterior doors (excluding overhead garage doors) with weather stripping around the edges.

  • Garage Access Door: Ensure the man door (3 feet by 7 feet) to the garage is sealed with weather stripping.

3. Sewer System Cleanouts

  • Ensure all sewer cleanouts are securely covered. Note: On septic systems, odors may not indicate missing covers, so verify during inspection.

4. Drywall Gaps Around HVAC Supplies, Returns, and Jump Ducts

Most homeowners are unfamiliar with this process, so here’s a detailed explanation:

  • Locate all HVAC supply registers in the home. These are the metal grills in your ceiling that push conditioned air into rooms.

  • Remove the metal grill entirely. You’ll see a rough edge between the drywall and a square or rectangular metal box called a "boot."

  • Seal the gap between the drywall and the boot with caulking.

  • Repeat this for all HVAC supplies, returns, and jump ducts. Returns are where filters are added, and jump ducts look like vents but don’t supply air.

5. Drywall Gaps Around Exhaust Fans

Many homeowners are unfamiliar with sealing exhaust fans. Here’s how to address this:

  • Locate fans in bathrooms and laundry rooms, which are used for reducing odors or humidity.

  • Remove the fan cover by pulling straight down. The cover is held in place by metal springs.

  • Seal the gap between the drywall and the exhaust fan boot with an appropriate sealant.

  • Replace the cover after sealing.

6. Sealing Around Recessed Lights

  • Inspect recessed lights for gaskets designed to prevent air leakage.

  • Ensure the gasket covers the entire drywall penetration. If gaps remain, use additional sealant to close them.

7. All other Drywall Penetrations

  • All homes are different, and they all have different features. Rather than list off 500 items, we are stopping the list here for drywall penetrations.

  • The majority of all drywall penetrations have been listed on this page. The remaining unique items, would been to be addressed while we are onsite.

Exhaust Fan Dampers

This item will likely need to be addressed by a mechanical contractor. Ensure that all exhaust fans have a damper installed to prevent unconditioned outdoor air from entering the home while allowing indoor air to be properly vented. Dampers can be installed in three locations: at the beginning, middle, or end of the exhaust line.

The Beginning

  • The damper closest to the exhaust fan is called an integrated exhaust fan damper. Many exhaust fans come with this type of damper pre-installed. Confirm its presence during installation, as it may be difficult for an inspector to verify before the blower door test.

The Middle

  • If an integrated damper cannot be installed, consider adding a butterfly damper along the duct line. To install, cut a section of the duct and splice in the damper.

  • Purchase a butterfly damper with the same diameter as the duct. Using the wrong size can restrict airflow or render the damper ineffective.

  • Note: Some ducts are insulated, making it difficult to measure their inner diameter. Check the duct's label for its size, which is typically 3 to 4 inches in diameter.

The End

  • For exhaust lines terminating at a wall, install a damper resembling a check valve or flapper at the end of the line. This ensures air can exit without re-entering the home. This method is typically not used for roof-penetrating exhaust lines.

By addressing these damper installations, you can ensure proper ventilation and reduce air infiltration, enhancing the home’s energy efficiency and comfort.