Building Codes Assistance Project

The air within homes can become stale from moisture, odors, and pollutants that penetrate the residence or are generated internally by human activity and out gassing from building materials and furnishings. A steady supply of fresh outdoor air can increase indoor air quality and improve occupant comfort. Historically, residential buildings have not had specific requirements for ventilation because leakage in envelope components and natural ventilation was considered adequate. As envelope construction practice has improved, the need to control air quality in the home has risen.

Any mechanical ventilation system will not reach its performance potential if components are poorly manufactured or installed improperly. Several factors contribute to poor performance including long duct lengths and compression in flexible ducts, resulting in a loss of ventilation rate and a significant increase in power and energy consumption by HVAC systems.

There are many new and innovative mechanical ventilation products available that are not specified by the model codes that can save energy, decrease utility bills, enhance thermal comfort, and improve indoor air quality. For more information, visit www.BuildingGreen.com.

The following section provides examples of these types of code improvement language or methodologies in these areas.

Policy Options

• More stringent requirements for ventilation fans, pollution or moisture-based source-point ventilation, and whole-house ventilation systems

  • Vermont Residential Building Energy Code Handbook, Edition 2.0 (September 2004)
    Section 2.1d -- Fan Requirements. Fans installed as part of a whole-house ventilation system must meet the following requirements (fans installed as local exhaust do not need to meet these requirements:
    • Durability: Fans must be rated for "continuous duty."
    • Efficiency: Efficiency: Single-port fans (those with only one connection to the conditioned space) must not exceed 50 watts as listed by the manufacturer. This refers to fan power only; it does not include power used for lights, heaters, nightlights, timers, etc. This power limit does not apply to multiport fans that have more than one connection to the living space.
    • Sound: Sound: Whole-house ventilation equipment located less than 4 feet from louvers, grilles or openings must have a sound rating no greater than 2 sones. Fans meeting the EPA ENERGY STAR® standard for household ventilation equipment are considered to meet the three requirements above.
    Section 2.1e Capacity. Whole-house ventilation systems that are not tested must be able to provide the minimum rated flow rates listed in Table 2.1. Alternatively, flow rates can be tested on site, using approved methods (i.e., a flow hood or a calibrated orifice combined with a digital manometer). If the system is tested, it does not need to meet the capacity requirements of Table 2.1, but it must provide a minimum of 15 cubic feet per minute (CFM) plus 15 CFM for each bedroom. (Consult link above for Table 2.1).

• Requirement for automatic controls or systems capable of being set remotely for continuous operation

  • Vermont Residential Building Energy Code Handbook, Edition 2.0 (September 2004)
    Section 2.1f -- Controls. The ventilation system must have an automatic control or be capable of being set remotely for continuous operation. Intermittently operated systems must have an automatic control capable of operating the system without the need for occupant intervention, such as a time switch. Twist or crank-style timers are not acceptable as controls for the whole-house system. Continuously operated systems must have a remotely mounted (i.e., not in the living space) on/off switch that is appropriately labeled. Continuously operated systems cannot have any local controls unless such controls affect the speed only and cannot turn the system off.