Basic Duct Sealing. By attending this session, participants will: Why do ducts need to be sealed?

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1 Basic Duct Sealing Lil Weston, Rappahannock Area Agency on Aging Fredericksburg, Virginia By attending this session, participants will: Identify health and safety issues involved with sealing duct systems; Gain a fundamental understanding of the importance of duct sealing; Identify different types of duct systems and design (flex, metal, duct board, floor panning, etc.); and Become familiar with the materials and tools necessary to properly seal duct systems. Why do ducts need to be sealed? The air in ducts is moved by a powerful fan. Duct leakage can create pressure imbalances in the building envelope, causing combustion safety issues and comfort issues. Duct leakage outside the building envelope decreases the efficiency of the entire HVAC system. Duct leakage can cause moisture and mold problems. Leaks in return ducts can draw in air from the attic, crawl space or attached garage.

2 Closed doors that prevent supply air from getting back to a return cause positive pressures in those rooms... meanwhile starving the return for air, causing negative pressures in the zone where the return is located Duct leakage can cause the same problems Supply Master Bedroom Bedroom Bath Utility Whole House Return in Hallway + Supply Supply + + Supply Supply Supply Living Room Supply Kitchen Supply Combustion Appliance Zone (CAZ) Air sealing or duct sealing may affect combustion-appliance venting by increasing house pressures or reducing the available supply of combustion air. After all weatherization materials have been installed, all crews or contractors must conduct worst-case draft testing and check the safety of all combustion appliances. Combustion Appliance Zone (CAZ) Return at furnace contributed to CAZ problem: -8 pa Gas water heater and clothes dryer in same room Replaced solid door with louver door CAZ went down to -4 pa

3 Air Leakage Requires All of the Following: Air Hole Pressure Difference 1 cfm in = 1 cfm out Air Moves from High Pressure Areas to Low Pressure Areas Air Moves through Ducts at a High Pressure Relative to the Outside of Ducts Ergo A hole in a duct leaks more air than the same size hole in the building envelope because the pressure difference across the hole in the duct is much greater. Conditions Necessary for Mold Growth: Mold Spores Present Available Nutrient Base Temperature Range: 35 to 120 F Relative Humidity of 70% or above at surface Duct leakage can increase the relative humidity inside the building envelope, crawl space, or attic enough to encourage mold growth.

4 Condensation at leaky duct/wall connection during cooling season Quantifying Duct Leakage The amount of duct leakage can be determined by using a calibrated fan such as the Duct Blaster. By itself, measures total duct leakage. Used with the blower door, can isolate duct leakage to outside, supply leakage, and return leakage. Finding Duct Leakage Pressure pan testing with the blower door will help to find the biggest leaks. Reversing flow on the blower door (pressurizing the house) is a good way to find leaks outside the building envelope. A digital camera or a seesnake is useful for looking inside the ducts.

5 Finding Duct Leakage Blowing smoke through a closed system helps to visually find duct leakage Prioritizing Duct Leakage Ducts located outside the thermal boundary or in a buffer zone like a ventilated attic or crawl space should be sealed. Leaks closer to the air handler are under higher pressure and are more important than leaks further away Prioritizing Duct Leakage - in relative order of importance Seal all return leaks in the combustion appliance zone to prevent this leakage from depressurizing the combustion zone and causing backdrafting. Plenum/air handler connection. Connections at branch takeoffs, especially the tabs. Joints in elbows. Connections to boots. Floor/wall/ceiling-to-boot connection

6 Prioritizing Duct Leakage - Beware! Floor and ceiling cavities used as return-air plenums. If possible, replace these with a duct and a filter grill or a grill straight off the furnace. Any building cavity used as a supply duct. If possible, replace these with a duct. These are nearly impossible to seal because you can hardly ever access all the framing details connecting these cavities to the outside. Sealing a building cavity used as a duct Entire cavity painted with mastic Sealing a building cavity used as a duct It s always good to have a tall skinny guy on the crew for those hard-toget-to places.

7 Sealing a building cavity used as a duct Entire cavity painted with mastic Panned return Panned Return

8 Prioritizing Duct Leakage Mobile Homes Base of furnace closet where furnace is seated over duct. End caps. Boot/duct and boot/floor connections. Crossover ducts in double-wide mobile homes. Branch lines. Ducts connecting outdoor unit for central cooling. Plumbing/electrical penetrations. Belly returns should be closed off. Typical Existing MH Furnace/Duct Connection Sealed (from inside) MH Furnace/Duct Connection

9 Sealed (from below) MH Furnace/Duct Connection MH End Cap - Leaky Mobile Home unsealed register

10 Mobile Home sealed register with boot Prioritizing Duct Leakage Small MultiFamily Party walls and between-floor joist spaces are usually very connected to the outside, so duct leaks in those areas are difficult to seal. Ducts are often run in drop ceilings and soffits, but those are often open or connected to the outside.

11 Prioritizing Duct Leakage Small MultiFamily This whole closet is the return plenum Would you want to circulate what is in this closet throughout the apartment? Prioritizing Duct Leakage Small MultiFamily Note condensation from line that runs to outside HVAC unit The zonal pressure in this cavity is 42 pa Prioritizing Duct Leakage Small MultiFamily Panned supply ducts in crawl space Pressure Pans 39.5 pa

12 Prioritizing Duct Leakage Small MultiFamily Register in upstairs apartment-gap between duct and wall Pressure pan pa Prioritizing Duct Leakage Small MultiFamily This is the duct Sealing Ducts - Materials Joints should rely on mechanical fasteners to prevent joint movement or separation. Tape should never be expected to hold a joint together nor expected to resist the force of compacted insulation or joint movement. Aluminum foil or cloth duct tape are not good materials for duct sealing - their adhesive often fails after a short time.

13 Sealing Ducts - Materials Duct mastic is a preferred duct sealing material because of its superior durability and adhesion. Apply at least 1/16-inch thick and use reinforcing mesh for all joints wider than 1/8 inch or joints that may experience some movement. Using mastic to seal ductwork Using mastic to seal ductwork

14 Using mastic to seal ductwork Using mastic to seal ductwork Return in ceiling Using mastic to seal ductwork Return in ceilingsealed

15 Sealing Ducts - Materials Two-part foam may be used to seal ducts in unconditioned areas. Two-part foam insulates as well as seals, saving time. Crew should wear respirator when applying two-part foam in poorly ventilated areas. Sealing Ducts - Materials Using two-part foam to seal ductwork Using two-part foam to seal ductwork

16 Sealing Ducts - Materials Using two-part foam to seal ductwork one product to seal and insulate ducts and walls Sealing Ducts - Materials Sealing Ducts - Materials Take care to get total coverage when using two-part foam to seal ducts sometimes it is better to use mastic to seal when the hand fits and the foam gun won t go.

17 Sealing Ducts Duct Chases If chase opening is large, seal with a rigid barrier such as firerated foam board, plywood or drywall, and seal the barrier to ducts with caulk or foam. Smaller cracks between the barrier and surrounding materials may be foamed or caulked. Sealing Ducts Flex-duct-to-metal joints: Apply mastic to the metal sleeve Clamp the flex-duct s inner liner over this strip of mastic with a plastic strap, using a strap tensioner. Clamp the insulation and outer liner with another strap. Support ducts with duct hangers to take the weight off the joints. Using mastic to seal flexduct Take-offs/connectors should be mechanically fastened to trunk

18 Using mastic to seal flexduct Mastic should be applied to connector, then the duct slipped over the connector Using mastic to seal flexduct Duct should be secured with a strap. Fiberglass mesh tape should be used on connections with a wide gap or junctions which may experience movement. Using mastic to seal flexduct Mastic may applied using a brush or by hand

19 Using mastic to seal flexduct Insulation may then be pulled down, then secured with another strap Sealing Ducts - Panned returns (or supplies) Mechanically fasten pan to joist if needed. Seal all edges and seams of panning material, including connections to ducts, or main trunk. Seal top of joist where it connects to the sub-floor. Gaps in the sub-floor must be sealed if present. Seal all accessible seams and connections from the return inside the house. That s all folks! Thank you for coming! Duct Demonstration in Exhibit Hall Block 5 Wednesday, 2:00-3:30pm Block 8 Thursday, 10:15 11:45 am