Undercut Doors

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Description

Ensuring Success

Scope

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

Duct Quality Installation

Option A.

Bedrooms pressure-balanced using any combination of transfer grilles, jump ducts, dedicated return ducts, and/or undercut doors to provide 1 square inch of free area opening per 1 CFM of supply air, as reported on the contractor-provided balancing report:

  1. Refer to the balancing report provided by the HVAC contractor for the bedroom air flows to size the transfer grilles and/or jumper ducts.
  2. Install and seal properly sized transfer grilles during framing. Both openings of the transfer grille must have the required free area.
  3. If transfer grilles are not used, install and seal jumper ducts during framing. Both openings and ducts must have the required free area.
  4. ENERGY STAR recommends that doors are undercut to approximately 3/4 inch above the finished floor.

Option B.

Bedrooms pressure-balanced using any combination of transfer grilles, jump ducts, dedicated return ducts, and/or undercut doors to achieve a Rater-measured pressure differential <= 3 Pa (0.012 in. w.c.) with respect to the main body of the house when bedroom doors are closed and the air handler is operating

  1. ENERGY STAR recommends that transfer grilles, jumper ducts or dedicated returns be installed and doors undercut to approximately ¾ inch above the finished floor.
  2. Test the pressures of each bedroom.
Rooms supply air flow
Free area opening required Height required for 10 in. wide transfer grille* Height required for 12 in. wide transfer grille* Height required for 14 in. wide transfer grille* Jumper duct diameter
CFM in2 in in in in
50 50 6.7 5.6 4.8 8
75 75 10 8.3 7.1 10
100 100 13.3 11.1 9.5 12
125 125 - 13.8 11.9 14
150 150 - - 14.3 14
175 175 - - - 16
200 200 - - - 16

* Assumes the net free area of the transfer grille as .75 in.

Option C.

Bedrooms pressure-balanced using any combination of transfer grilles, jump ducts, dedicated return ducts, and/or undercut doors to achieve a Rater-measured pressure differential <= 3 Pa (0.012 in. w.c.) with respect to the main body of the house when bedroom doors are closed and the air handler is operating

  1. ENERGY STAR recommends that transfer grilles, jumper ducts or dedicated returns be installed and doors undercut to approximately ¾ inch above the finished floor.
  2. Test the pressures of each bedroom.
Rooms Pressure (PA) with Respect to Main Body
Bedroom 1  
Bedroom 2  
Bedroom 3  
Bedroom 4  
Bedroom 5  
Bedroom 6  

 

ENERGY STAR Notes:

This checklist item does not apply to ventilation ducts. For HVAC system with multi-speed fans, the highest design fan speed shall be used when verifying this requirement.

Pressure Relief Tips

  • ENERGY STAR recommends that HVAC contractors install transfer grilles, jumper ducts, or dedicated returns.
  • ENERGY STAR recommends that framers undercut doors to approximately ¾ inch above the finished floor.
  • If transfer grilles are used, contractors must install and seal properly sized transfer grills according to the load calculation.
  • If jumper ducts are installed, contractors must seal all seams, gaps, and holes of the ducts and connections.
  • If return ducts are installed, contractors must seal all seams, gaps, and holes of the return duct system with mastic and seal the return box to the floor, wall, or ceiling with mastic, caulk, and/or foam.

Pressure Testing Tips

  • Prior to testing pressures:
    • Verify all supply and return terminations are unrestricted.
    • Turn the HVAC system on to cooling mode. If there is no cooling mode, set it to heating mode.
    • Verify air is blowing out of the supply terminations.
  • Verify the reference pressure is measuring the outdoor pressure.
  • Test all pressures by placing the pressure measuring device in each bedroom with the door shut.

Training

Right and Wrong Images

Presentations

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Videos

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CAD Images

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Compliance

ENERGY STAR Version 3, (Rev. 07)

HVAC System Quality Installation Rater Checklist, Duct Quality Installation. This checklist item does not apply to ventilation ducts. For HVAC system with multi-speed fans, the highest design fan speed shall be used when verifying this requirement.

Associated Air Barrier Council

Associated Air Barrier Council 2002. AABC National Standards for Total System Balance 2002. The manual details the minimum standards for total system balance.

National Environmental Balancing Bureau

National Environmental Balancing Bureau (NEBB) Section 15990 – Testing, Adjusting, and Balancing. NEBB is a certification association whose members perform testing, adjusting and balancing (TAB) of heating, ventilating, and air-conditioning systems and commission and retro-commission building systems. This document is the TAB procedural standards.

More Info.

Case Studies

None Available

References and Resources*

  1. Author(s): Associated Air Barrier Council
    Organization(s): Associated Air Barrier Council
    Publication Date: January 2002

    Standards book discussing changes, additions and enhancements over the 5th edition of the AABC National Standards for Total System Balance.

  2. Author(s): EPA
    Organization(s): EPA
    Publication Date: June 2013

    Standard document containing the rater checklists and national program requirements for ENERGY STAR Certified Homes, Version 3 (Rev. 7).

  3. Author(s): National Environmental Balancing Bureau
    Organization(s): National Environmental Balancing Bureau
    Publication Date: January 2005

    Standard that includes testing, adjusting and balancing (TAB) to produce design flows for air and hydronic systems.

Last Updated: 08/15/2013

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