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Air handler platforms used as return air plenums can draw air from vented attics and crawlspaces through other connected framing cavities
Bedrooms pressure-balanced and provide 1 sq. in. of free area opening per 1 CFM of supply air or achieve a Rater-measured pressure differential ≤ 3 Pa
Bedrooms pressure-balanced and provide 1 sq. in. of free area opening per 1 CFM of supply air or achieve a Rater-measured pressure differential ≤ 3 Pa
Building cavities not used as supply or return ducts unless they meet Items 3.2, 3.3, 4.1, and 4.2 of this Checklist
Cavity used for return is not insulated and is not air sealed, which will pull in air from outside
Cavity was not air sealed
Compact duct design layout
Consider using a metal duct elbow instead of flex duct at boot connections to prevent compressions
Coordinate with other trades including framers, plumbers, and electricians to prevent needless looping of flex duct
Cut the duct to the length needed
Door has been undercut to allow for specified amount of air flow therefore contributing to pressure balancing
Door is not undercut therefore not contributing to pressure balancing
Duct is compressed
Duct is compressed
Duct is kinked in cavity
Duct is run straight and supoprted properly
Duct is run straight and supported properly
Duct to boot connection of jump duct is properly sealed with mastic
Duct to boot connection of jump duct not fastened and sealed
Ducts are run straight and supported properly
Ducts crammed into cavity, kinked and sharply bent
Ducts properly installed without compression and appropriately supported
Ducts properly installed without compression and appropriately supported
Ducts sagging because supports not installed at regular intervals
Ducts should not be located in exterior wall cavities
Ducts well supported
Ducts well supported
Ducts well supported
Ducts well supported by framing and straps as needed
Ensure that the air handler location does not conflict with duct routing
Example of an HVAC installer’s balancing report form
Excessive length of duct installed
Excessive length of duct installed causing sharp bends
Excessive length of duct installed causing sharp bends
Fan housing was oriented in the correct direction to allow proper exhaust duct installation
Fan housing was oriented in the correct direction to allow proper exhaust duct installation
Flex duct compressed by plumbing pipes
Flex ducts are compressed
Flex ducts may rest on ceiling joists or truss supports
Flexible Duct Materials & Assembly
Flexible ducts in unconditioned space not installed in cavities smaller than outer duct diameter; in conditioned space not installed in cavities smaller than inner duct diameter
Flexible ducts supported at intervals as recommended by mfr. but at a distance ≤ 5 ft
Floor joist cavities can make acceptable duct chases
Floor joist cavities can make acceptable duct chases
Framing allowed duct work to be properly installed without compression
Grill and duct size based on calculated requirements for net free area
Hanger straps should be at least 1.5 inches wide
HVAC duct layout
HVAC ducts, cavities used as ducts, and combustion inlets and outlets may pass perpendicularly through exterior walls but shall not be run within exterior walls unless at least R-6 continuous insulation is provided on exterior side of the cavity
If a dropped soffit is used to house a duct, the soffit space must equal the duct diameter plus the insulation thickness
If airflow must be limited to a supply register, use balancing dampers at the trunk line rather than looping duct to control airflow
If HVAC duct must be installed in an exterior wall, separate it from the exterior with at least R-6 of continuous rigid insulation
If wall registers are desired, install HVAC ducts in interior wall cavities
Inadequate amount of insulation installed with compression, misalignment, and voids
Install bottom layer of rigid insulation
Install ducts without excessive coils or loops
Install ducts without kinks or sharp bends
Install supply registers in floors or ceilings to avoid routing ducts through exterior walls
Install supports every 5 feet so that maximum allowable sag in flexible duct is no more than one-half inch per foot
Install supports every 5 feet so that maximum allowable sag in flexible duct is no more than one-half inch per foot
Lay out duct so that no radius of a bend or turn is less than the diameter of the airway
Mechanical damper installed
Metal strap is too small and is compressing duct
Metal strap is too small and is compressing duct
No insulation installed in cavity and not air sealed
No mechanical damper installed
Open floor trusses used as return air plenums can draw air from any place connected to that floor
Provide for pressure balancing between bedrooms and the rest of the house.
Pulling flex duct taut when installing greatly reduces the amount of friction caused by the ducting
R-6 flexible duct has 2 inches of insulation around the inner liner so a 12-inch duct requires a 16x16-inch chase
Recessed can light is compressing duct work
Return box has been properly sealed with mastic
Return box has not been sealed
Return duct has been properly sealed with mastic
Return has not been sealed
Run-out ducts are installed over partition walls
Some builders create pan joists by attaching a solid sheet good to the bottom of a floor joist to create a return air pathway
Straps are spaced too far apart causing the straps to compress the duct under its own weight
The drywall above the dropped ceiling duct chase extends beyond adjoining top plates for a continuous air barrier
There should be less than 2.5 inches per each five foot of duct length
Transfer grill not sealed
Transfer grill sealed with mastic
Twisting and compressing flex duct will block air flow
Well sealed duct lifted into raised ceiling chase
Wrong – Excessive bends in flex ducts
Wrong – Flex duct is coiled and looped
Wrong – Flex duct is pinched