Provide for pressure balancing between bedrooms and the rest of the house.
- Install ducted returns or a combination of ducted returns, transfer grilles, jump ducts, and/or door undercuts in bedrooms to allow pressure balancing between bedrooms and the rest of the house in homes with ducted heating and cooling systems by providing a path for stale air to return to the return side of a central air handler.
- ENERGY STAR Certified Homes requires that the dedicated return ducts, transfer grilles, jump ducts, and/or door undercuts provide 1 square inch of free area opening per 1 CFM of supply air, as reported on the contractor-provided balancing report. Or, that the dedicated return ducts, transfer grilles, jump ducts, and/or door undercuts together achieve a Rater-measured pressure differential of ≤3 Pascals (0.012 inch water column) with respect to the main body of the house when bedroom doors are closed and the air handler is operating.
- If dedicated return ducts are installed in each bedroom, 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.
- If transfer grilles or jump ducts are used, refer to the balancing report provided by the HVAC contractor for the bedroom air flows to size the grilles or ducts. Ensure that both openings have the required free area. Seal all seams, gaps, and holes in the ducts and connections.
- If door undercuts are used, framers should cut the bottom of the doors to approximately ¾ inch above the finished floor.
- Test the pressure differential with the bedroom doors closed.
See the Compliance Tab for related codes and standards, and criteria to meet national programs such as ENERGY STAR Certified Homes, DOE’s Zero Energy Ready Home program, and EPA’s Indoor airPLUS.
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
- Before ceiling drywall is installed, determine a location between the ceiling rafters in each room. Install the registers and insulated flex duct.
- 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.
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.
No climate specific information applies.
ENERGY STAR Certified Homes (Version 3/3.1, Revision 08), Rater Field Checklist
6. Duct Quality Installation
6.2 Bedrooms pressure-balanced using any combination of transfer grills, jump ducts, dedicated return ducts, and / or undercut doors to achieve a Rater-measured pressure differential ≤ 3 Pa with respect to the main body of the house when all bedroom doors are closed and all air handlers are operating. See Footnote 34 for alternative.34
(34) Item 6.2 does not apply to ventilation or exhaust ducts. For an HVAC system with a multi-speed fan, the highest design fan speed shall be used when verifying this requirement. As an alternative to the 3 Pa limit, a Rater-measured pressure differential ≤ 5 Pa is permitted to be used for bedrooms with a design airflow ≥ 150 CFM. The Rater-measured pressure shall be rounded to the nearest whole number to assess compliance.
ENERGY STAR Revision 08 requirements are required for homes permitted starting 07/01/2016.
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. 2002. AABC National Standards for Total System Balance 2002. The manual details the minimum standards for total system balance.
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.
This topic is not specifically addressed in the 2009 IECC.
This topic is not specifically addressed in the 2009 IRC.
This topic is not specifically addressed in the 2012 IECC.
This topic is not specifically addressed in the 2012 IRC.
Jump Ducts = Comfort Crossover Vent