Jump Ducts

Please Register or Login to Provide Feedback.

Climate

No climate specific information applies.

Please Register or Login to Provide Feedback.

Description

For central “forced air” furnace and air conditioning systems to operate properly, the HVAC distribution system should be designed with adequate supply and return registers to provide conditioned air to all parts of the house and return stale air to the furnace for reconditioning. Most HVAC distribution systems are designed with at least one supply register in each room; however, typically only a few larger return registers are installed in a home—usually one on each floor level in a central location such as a central hallway floor or ceiling. To ensure that “stale” air is able to return to these central returns from rooms such as bedrooms or offices that have closeable doors, builders will often rely on door undercuts. These can be inadequate for providing enough air flow, especially when carpet is installed. Inadequate return air pathways can cause pressure imbalances from room to room, which can cause drafts and temperature differences between rooms or floors, leading to comfort complaints. These imbalances can overly pressurize closed rooms forcing conditioned air into exterior walls, which could result in condensation issues in wall cavities and can cause the furnace and air conditioning equipment to work harder than necessary. One option is to install a return air duct in each room. Other options include installing jump ducts or transfer grilles in the rooms that are often closed. A jump duct is a short piece of insulated flex duct (typically 10-inch-diameter duct) installed in the attic and attached to ceiling registers in the closed room and a common space to provide a return air pathway between the two areas.

Jump ducts may be installed by the HVAC installer. This task should be included in the contract for the appropriate trade depending on the workflow at specific job sites.

How to Install a Jump Duct

  1. Before ceiling drywall is installed, determine a location between the ceiling rafters in each room. Install the registers and insulated flex duct.
  2. After ceiling drywall is installed, seal the registers to the ceiling drywall with caulk. Seal the duct to the register boots with mastic or plastic or metal ties and approved metal tape, not duct tape.

Installing jump ducts from room to room is one way to balance pressures 

Figure 1 - Installing jump ducts from room to room is one way to balance pressures  Reference

A jump duct is installed in the ceiling to connect a closed room with an open area to provide a passive air pathway to the central return air register

Figure 2 - A jump duct is installed in the ceiling to connect a closed room with an open area to provide a passive air pathway to the central return air register  Reference

 

Ensuring Success

Duct blaster testing equipment can be used with a pressure pan as part of HVAC commissioning to determine pressure differences at each supply register and to determine whether adequate pathways exist for air to return to centrally located returns.

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

Pressure Balancing Bedrooms

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 grills during framing. Both openings of the transfer grill 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 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.

Additional Information
For additional information and specific duct testing protocols please refer to RESNET Chapter 8 (Standard for Performance Testing and Work Scope: Enclosure and Air Distribution Leakage Testing).

Training

Right and Wrong Images

Presentations

None Available

Videos

None Available

CAD Images

None Available

Compliance

ENERGY STAR Version 3, (Rev. 07)

HVAC System Quality Installation Rater Checklist, Duct Quality Installation. This 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.

Air Conditioning Contractors of America

Air Conditioning Contractors of America. 1995. Manual T Air Distribution Basics for Residential and Small Commercial Buildings. Manual T provides details on selecting, sizing, and locating supply air diffusers, grilles and registers, and return grilles.

Associated Air Balance Council

Associated Air Balance 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.

2009 IECC

This topic is not specifically addressed in the 2009 IECC.

2009 IRC

This topic is not specifically addressed in the 2009 IRC.

2012 IECC

This topic is not specifically addressed in the 2012 IECC.

2012 IRC

This topic is not specifically addressed in the 2012 IRC.

More Info.

Case Studies

  1. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: December 2009

    Case study about new home construction in the hot-humid climate, optimizing thermal enclosure, HVAC, water heating and lighting measures.

  2. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: April 2012

    Case study about design and testing 10 high-performance homes in Farmington, Connecticut.

References and Resources*

  1. Author(s): Baechler, Gilbride, Hefty, Cole, Williamson, Love
    Organization(s): PNNL, ORNL
    Publication Date: September 2010

    Report providing builders in marine climates with guidance for building homes that have whole-house energy savings of 40% over the Building America benchmark with no added overall costs for consumers.

  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): BSC
    Organization(s): BSC
    Publication Date: May 2009

    Information sheet about transfer ducts and grilles.

Last Updated: 08/15/2013

Mobile Field Kit

The Building America Field Kit allows you to save items to your profile for review or use on-site.