SPECIFICATION FOR INSPECTION OF DUCT AIR LEAKAGE by fxb21275

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									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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