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Balanced Supply plus Exhaust

Installed correctly, a whole-house fresh air system helps ensure a healthier indoor environment.

Preparation
The flow rate any of existing bath exhaust fans shall be tested. If the flow rate does not meet the target ventilation rate specified below, if fan noise is excessive, or if the bath fan is not present, a bathroom exhaust fan shall be installed according to the Home Improvement Expert Checklist: Bathroom Exhaust Fan.
For continuous operation, the target ventilation rate for the home shall be based on house size as follows: 50 cfm for up to 1,500 ft², 70 cfm for 1,501 to 2,500 ft², and 100 cfm over 2,500 ft². For intermittent operation, the average air flow shall meet the minimum target ventilation rate specified above (e.g., if the controller operates the air handler fan for a minimum of 20 minutes each hour, then three times the target ventilation air flow is needed).
An outdoor air intake location shall be selected that is close to the return plenum of the central air handler and will provide a short, straight, unobstructed path from the air intake to the return plenum to provide unrestricted air flow. The equivalent length of the duct run should be as short as possible. "Equivalent length" shall be calculated in accordance with ANSI/ACCA Manual D Residential Duct Systems.
The air intake should open to the outdoors, not to an attic, basement, garage, or crawlspace. The location should be away from garages or parking areas; at least 10 feet from any exhaust termination; and accessible from the ground for cleaning and maintenance, but well above the snow level. The air intake should be equipped with an air filter that is MERV 11 or better. The pressure drop across the filter shall be measured and verified to match equipment capabilities.
If the HVAC air handler has a PSC (permanent split capacitor) motor, the PSC motor shall be replaced with a variable-speed ECM or BPM motor.
A controller shall be selected that is compatible with the existing air handler and control system.
Installation
Outdoor air intakes shall be equipped with screens to keep out insects and debris, integrated with siding and flashed properly to prevent water intrusion, and caulked where the edges of the duct meet the exterior walls or ceilings to limit the infiltration of exterior air into the home.
The balancing damper and the controller shall be adjusted so that the specified amount of outdoor air is introduced into the system at the desired schedule.
The outside termination of any exhaust ducts shall be covered with louvers, a screen, or a grille.
All duct seams and connections shall be sealed with mastic or UL 181 tape.
Ducts installed outside of the thermal envelope shall be insulated to a minimum of R-8.
Commissioning
The ventilation rate shall be measured using a flow hood, flow grid, or anemometer, in accordance with test procedures listed in ANSI/RESNET/ICC 380-2016, to ensure that the fan is providing the minimum ventilation rate specified above.
All operation and maintenance procedures shall be reviewed with the homeowner (e.g., how and when to clean the intake screen).
At the completion of the work, a radon test kit shall be provided to the homeowner to measure post-retrofit radon levels and remediate if radon levels exceed EPA limits.

BASC Guides

Guide describing how to evaluate existing ventilations systems before performing home upgrades.

Guide describing how to select and install whole-house ventilation systems for existing homes.

Guide describing how to install continuously operating exhaust fans.

Tips to Sell Quality Installed Home Improvements

Home Improvement Expert (HIE) is a valuable tool for organizations committed to quality installed work. The following tips help optimize the value of this tool when selling home improvements:

  • Be the Expert: Take advantage of Building America Solution Center comprehensive guidance on ‘Existing Home’ retrofits.
  • Earn Trust: Inform homeowners how your work conforms to U.S. Department of Energy (DOE) world-class expert guidance and recommend homeowners visit the DOE website as evidence these are indeed official best practices.
  • Clarity with Contrast: Tell prospective homeowner clients to compare your expert recommended best practices with other contractors.
  • Ensure Equivalent Pricing: Tell prospective homeowner clients to insist other bids also include DOE checklists to ensure equivalent quality work.
  • Translate Value: Note your company uses DOE HIE Checklists based on world-class expert recommendations for home improvements on all your public-facing communication including websites, advertising, and signage.
  • Create Emotional Experiences: Provide visual evidence contrasting the difference between poor and high quality work such as infrared images for good and bad insulation and air sealing; pre- and post-energy bills following quality installed work; short and long warranties for standard and high-efficiency equipment; and charts showing amounts of contaminants in homes that can be reduced with effective fresh air systems.

Balanced Supply plus Exhaust Background

Air handler controller

Contaminants in homes can trigger asthma and allergy attacks as well as other health problems. Whole-house fresh air systems effectively dilute these contaminants. Balanced systems provide effective ventilation by bringing fresh air into the home through dedicated fresh air ducts equipped with filters rather than through unknown sources like cracks in the building envelope. This intake air is balanced with electronically controlled exhaust fans to maintain even air pressures throughout the home. Electronic controls are used to operate the air handler fan of the central heating and cooling system to periodically draw a set amount of fresh air into the home throughout the day, even when the thermostat is not calling for heating and cooling.