Appendix F SPECIFICATION FOR INSPECTION OF DUCT AIR LEAKAGE Specification for Inspection of Duct Air Leakage A detailed inspection of the existing air a different material, such as flexduct. Leaks are distribution system will be performed in often caused by circumferential joints that are existing housing units that will retain the unsealed or that are initially sealed with only system. The purpose of this inspection is to fabric duct tape, which deteriorates (see evaluate the condition of the system relative to Fig. F.1). Joints also may be poorly sealed or continued long-term use (verify that it is unsealed at the junction between the heating and economical to retain the current system) and to cooling system and the supply trunk. identify the location and type of major duct Junction boxes are fabricated of sheet metal leaks that need to be sealed during revitalization. or ductboard to divide supply air into two The purposes of a visual inspection of the separate branch flows at the end of a supply air distribution system are as follows: trunk. Leaks at junction boxes can occur at the seams of the box if duct tape is the only sealant. • to evaluate the need to replace all or parts of Also, duct connections to the box can leak if the system because of general deterioration they are unsealed or sealed only with fabric duct of the system; tape. • to determine whether the localized damage Connections at supply registers often leak that is responsible for excessive duct because of a poor seal between the branch leakage can be repaired; ductwork and the connecting “boot.” Poor seals • to determine whether improper materials or between the connecting boot and the register supports are present; and itself also contribute to leaks. Figure F.2 shows • to evaluate whether duct insulation is a leak that occurs when a connecting metal boot adequate for continued use of the system. is incorrectly installed to the supply register. Lack of a mechanical fastener often Inspection for leaks is based on visual contributes to the formation of joint leaks. A observation enhanced by depressurizing the mechanical fastener is especially needed to housing unit with a blower door (or pressurizing connect flexduct to supply registers to ensure a the ducts with a fan) to allow detection of leaks long-lasting seal. Plastic ties, especially if used through observation of airflow with a synthetic in a hot attic, can become loose and slip off the “smoke” source. boot connection. Connecting boots fabricated from ductboard BACKGROUND may have poor seals where they slip over the supply register. Supply System Leaks in the supply ducts of the air Return System distribution system are important because Leaks in return ducts are often more conditioned air is directly lost through them common than leaks in supply ducts. Return before it can be delivered to the house. Also, leaks are important because they pull hot or cold dominant supply leakage can result in air and pollutants into a house from attics and depressurization of a house, increasing the other unconditioned locations. Also, dominant infiltration rate of the house whenever the return leakage can result in pressurization of a system operates. house, increasing the loss of conditioned air Main supply ducts are often fabricated from through leaks in the building envelope. sheet metal or ductboard, with branches to individual registers fabricated from the same or SPECIFICATION FOR INSPECTION OF DUCT AIR LEAKAGE F-1 (a ) (b ) (c ) (d ) Fig. F.1. Circumferential joints in ductwork often deteriorate and leak if they lack mechanical fasteners and were initially unsealed or sealed only with fabric tape. F-2 SPECIFICATION FOR INSPECTION OF DUCT AIR LEAKAGE Fig.F.2. A sheet metal boot in a newly installed duct system is improperly installed, creating a 1/2-in. gap between the boot and the supply register. The importance of return leakage was not metal and ductboard, or building cavities are recognized in the past, general thinking being often used. Return ducts constructed from that return leaks were a way to provide “fresh” traditional duct materials are prone to the same air to a house. Therefore, it has been common leaks described for supply ducts. A common practice to downplay the importance of problem is the connection of a return duct to the constructing airtight return systems. Unsealed heating or cooling system or a junction box at cavities in the building structure—walls, floor the unit (see Fig. F.4). joists, stud bays—have often been used as parts Building cavities used as part of the return of the return “ductwork.” system are often leaky and are inappropriate Return grills are common leak locations substitutes for dedicated ducts. Examples when gaps are left between the grill and the include panned floor joist cavities formed by wall, ceiling, or floor to which it is mounted. Air attaching sheet metal between floor joists, stud can be sucked into the return from the outside, bay cavities formed by wall studs and drywall, attic, or other unconditioned spaces through the and floor truss cavities formed within floor wall, ceiling, or floor cavity. Figure F.3 shows a trusses. Joints and penetrations in these cavities leak to a wall cavity behind a wall-mounted grill. are typically not sealed, allowing unconditioned Return ducts that connect the return grill to air to be drawn into the return from all parts of the heating and cooling system are usually the housing unit and the outside. These leaks constructed from duct materials such as sheet can also allow return air to be drawn from SPECIFICATION FOR INSPECTION OF DUCT AIR LEAKAGE F-3 (a) (b) Fig. F.3. A leak to a wall cavity located behind a wall-mounted grill (a). The joints in the ductwork behind the grill are also deteriorated and leaking (b). F-4 SPECIFICATION FOR INSPECTION OF DUCT AIR LEAKAGE Fig. F.4. Use of duct tape rather than mechanical fasteners to secure the connection of a return duct to a junction box at an attic-mounted evaporator allowed the joint to fail, forming a significant return leak. adjacent townhouse units, which increases the to be drawn into the return from all connected infiltration rate in the adjacent housing unit. spaces in the house and outside. Connections between ducts and these building cavities frequently are not sealed, and their Air Handlers failure creates large leakage areas (see Fig.F.5). Heating and cooling units located in a Leaks at air handlers are important because garage are frequently mounted on a plywood the positive (supply) and negative (return) box that is a return plenum. Units that are pressures at this location are the highest in the installed in an interior closet often use the entire system. Incorrectly matched equipment sections closet as a return plenum or sit upon a return and poor installation (frequently caused by tight plenum built using a raised floor and the closet quarters) can produce large leakage sites (see walls. These plenums and closets are often not Fig. F.7). Even small leakage areas such as sealed, allowing nonconditioned air to be drawn “knockouts” for wiring and equipment lines and into the return system. Figure F.6 shows a return cracks between panels can represent significant plenum built in a closet with unfaced interior leakage paths (see Fig. F.8). walls and penetrations for plumbing and electrical lines that allow air to be drawn from Supports for Ductwork the outside and attic. Ductwork can be hung from floor joists in Return plenums are frequently built behind crawl spaces and basements, and from roof the return grill, formed by spaces between floors trusses in attics. Metal straps or bands are used or under stairwells. Again, unsealed walls and to provide support for ductwork. If the supports penetrations serve as leakage sites, allowing air SPECIFICATION FOR INSPECTION OF DUCT AIR LEAKAGE F-5 Fig. F.5. The joint between a return duct and a building cavity used as a return duct was not sealed and mechanically fastened and, following failure, created a large leakage area. Fig. F.6. Unfaced interior walls and unsealed penetrations for plumbing and electrical lines in this return plenum allow unconditioned air to be drawn into the return from the attic or the outside. F-6 SPECIFICATION FOR INSPECTION OF DUCT AIR LEAKAGE Fig. F.7. An evaporator that is physically too large for and poorly mounted to the furnace created a large supply leak. Metal-faced duct tape used to seal the leak had deteriorated. are inadequate or fail, the duct can drop and installed without any insulation, even when open a leak at joints adjacent to the failure located in unconditioned spaces such as attics, location. crawl spaces, and unheated basements. Duct Insulation INSPECTION PROCEDURE All supply and return ductwork in Identify on the Duct Inspection Checklist unconditioned spaces should be insulated or the installation at which the unit is located. have insulation equivalent to current duct Assign a unique identification number to the insulation standards, nominally a level of at housing unit, or use the identification number least R-6. Older metal duct systems often were previously assigned to the housing unit if an SPECIFICATION FOR INSPECTION OF DUCT AIR LEAKAGE F-7 Fig. F.8. An unsealed “knockout” for wiring and refrigerator lines and a poorly fitting panel on this attic-mounted evaporator allow attic air to be drawn into the return system. energy inspection was performed by the A/E, a plenums and return ducts; and (4) location and blower-door inspection of the house was type of building cavities used in the duct performed, or the tightness of the ducts were system. The plan shall include attic, basement, measured. Document the address of the and living-level schematics as needed. The plan inspected unit, inspector, and inspection date. shall be used to indicate the location of any Prepare a schematic plan of the air repairable leaks found during the inspection. distribution system relative to the floor plan of The following diagnostics shall be the unit. The plan shall indicate the following performed to identify the location of repairable major features: (1) location of the heating and duct leaks: cooling equipment; (2) location of supply ducts and junction boxes; (3) location of return F-8 SPECIFICATION FOR INSPECTION OF DUCT AIR LEAKAGE 1. Prepare the house as follows for blower-door 8. Repeat steps 4-7 for each register in the testing: house. Move in a clockwise rotation in each room if more than one register is present. • Close all windows and outside doors. 9. Depressurize the house to 25–30 Pa. • Close the damper and outside air supply 10. Visually inspect the duct system for leakage to the fireplace (if present). using a source of synthetic “smoke” to aid • Close and secure the attic access hatch. in detecting leaks. Document the location of • Turn off all air handler and exhaust fans. repairable duct leaks on the Duct Inspection • Open all supply and return registers (if Checklist and the duct schematics. Indicate present). the magnitude of the duct leak on the duct • Remove filters from the air distribution schematic using the following key: system (if present). X—small leak, XX—medium leak, and • Turn off all combustion appliances. XXX—large leak. • Close doors to unconditioned utility 11. Turn off the blower door and return the closets or other unconditioned spaces. house to its original condition. • Open all interior doors (except for closets) so that all interior conditioned The airtightness of the duct system should space is connected, including have been previously measured following a conditioned basements. separate procedure. If the leakage rate of the ducts is less than 150 cfm at 50 Pa, then few 2. Install a blower door on the house following repairable duct leaks should be expected. The the manufacturer’s recommendations. pressure readings made in Step 6 help guide the 3. Depressurize the housing unit to 50 Pa. visual inspection to identify the primary 4. Working on one register at a time, create a locations for duct leakage by identifying the temporary airtight barrier across the register leakiest ducts. The higher the pressure opening by placing a “pressure pan” over difference, the greater the amount of duct the register or using temporary (masking or leakage expected in that leg of the duct system. painter’s) tape applied over the face of the Pressure differences of less than 2 Pa indicate grill. little duct leakage. 5. Place a pressure gauge near the register to be The following points shall be considered in tested, and level and zero the gauge. determining if a duct leak should be identified 6. Measure the pressure difference across the as repairable: cover (the difference in pressure inside the duct relative to the house) by connecting the • Leaks closest to the air handler are gauge to the pressure pan or inserting a important as the pressure driving forces are small probe through the duct cover. Record greatest at the air handler. the pressure difference on the Duct • Leaks in return ducts located in the same Inspection Checklist. zone as combustion equipment should 7. Remove the temporary barrier across the almost always be sealed to prevent possible register, and leave the register open. backdrafting of combustion appliances. SPECIFICATION FOR INSPECTION OF DUCT AIR LEAKAGE F-9 MILITARY FAMILY HOUSING: DUCT INSPECTION CHECKLIST Housing unit ID: __________ Installation: Unit address: Date: Inspectors: Duct pressure (Pa)a Room Floorb Supplyc Returnc Comments Foyer Living Dining Kitchen Family Bath No. 1 Master Bdrm. Bath No. 2 Brdm. No. 2 Bdrm No. 3 Bdrm. No. 4 Bath No. 3 Hallway No. 1 Hallway No. 2 Utility a With unit depressurized to 50 Pa and duct sealed. b Main, 2nd, 3rd, basement. c If more than one register, list data in clockwise rotation from main entrance to room. F-10 SPECIFICATION FOR INSPECTION OF DUCT AIR LEAKAGE DUCT INSPECTION CHECKLIST — SUPPLY LEAKS House ID:____________ Duct Duct Duct Joint seal/ Number Leak Comments and functiona typeb locationc reinforcementd of leaks Leak locations sizee recommendationsf a ST—supply trunk; SB—supply branch; JB—junction box; SR—supply register; HU—HVAC unit. b Duct types: DB—ductboard, SM—sheet metal, FD—flexduct, X—other. c Location: A—attic, B—basement, C—crawl space, G—garage, X—other. d Joint sealant/reinforcement for circumferential joints: M—mastic; MT—metal-faced tape; FT—fabric tape; MS—metal screws; MB—metal band; PB—plastic band; N—none. e Leak size: width and length of gap, inches. f Cause of leak—damaged duct, deteriorated seal, unsealed penetration, other. Repair recommendation—replace duct, repair joints or penetrations. DUCT INSPECTION CHECKLIST — RETURN LEAKS House ID:____________ Duct Duct Duct Joint seal/ Number Leak Comments and functiona typeb locationc reinforcementd of leaks Leak locations sizee recommendationsf a RG—return grill; RD—return duct; RP—return plenum. b Duct types: DB—ductboard, SM—sheet metal, FD—flexduct, SR—sheetrock, X—other. c Location: A—attic, B—basement, H—hallway, C—crawl space, G—garage, X—other. d Joint sealant/reinforcement for circumferential joints: M—mastic; MT—metal-faced tape; FT—fabric tape; MS—metal screws; MB—metal band; PB—plastic band; N—none. e Leak size: width and length of gap, inches. f Cause of leak—damaged duct, deteriorated seal, unsealed penetration, other. Repair recommendation—replace duct, repair joints. DUCT INSPECTION CHECKLIST — BUILDING CAVITIES House ID:____________ Duct Cavity Duct Number Leak Comments and functiona typeb locationc Joint seald of leaks Leak locations sizee recommendationsf a RD—return duct; RP—return plenum. b Cavity types: SB—stud bay, FT—floor truss, PFT—panned floor truss, F—floor. c Location: IW—interior wall, EW—exterior wall, B—basement, C—crawl space, G—garage, X—other. d Joint sealant: M—mastic; MT—metal-faced tape; FT—fabric tape; N—none. e Leak size: width and length of gap, inches. f Cause of leak—damaged duct, deteriorated seal, unsealed penetration, other. Repair recommendation—replace duct, repair joints. DUCT INSPECTION CHECKLIST — INSULATION AND SUPPORTS House ID:____________ Duct Duct Duct Insulation Insulation Duct Support functiona typeb locationc typed conditione supportf failureg Comments a ST—supply trunk, SB—supply branch, RD—return duct, RP—return plenum, JB—junction box. b Duct types: DB—ductboard, SM—sheet metal, FD—flexduct, X—other. c Location: A—attic, CB—conditioned basement, UB—unconditioned basement, C—crawl space, G—garage, H—hallway, X—other. d Batt, R=___; Blanket, R=___; Ductboard, R=___; Flexduct, R=___; Other, R=___; Other, R=___; None. e Good—no repair; Fair—minor repairs; Degraded—replace. f A—adequate support, I—inadequate support (>10 ft span). g L—loose attachment, B—broken support, N—none.
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