How to Meet Code when Specifying Ceiling Exhaust Fans for Multifamily Projects

In accordance with ASHRAE 62.2, recent changes to IECC and the ENERGY STAR® Multifamily New Construction (MFNC) program have increased minimum ventilation rates. To meet code, mechanical exhaust and whole-unit ventilation performance must be measured, verified, and documented. The inability to meet the mandatory airflow rate can result in costly alterations to mechanical systems, fan capacities, and ductwork installations in multifamily construction.

What factors affect airflow (CFM)?

In a study conducted by Steven Winter Associates, Inc., a clear association was found between ductwork configurations and increased levels of static pressure. Figure 1 below shows that while the ideal installation (A) resulted in a static pressure of 0.15 in. wg, the other installations more reflective of common scenarios (B-G) ranged from 0.30 to 0.45 in. wg.

Figure 1: Impact of Duct Configuration on Static Pressure (Source: Steven Winter Associates, Inc.)

Residential-grade bathroom exhaust fans are specified on rated performance at 0.1 in. wg as the industry standard, or 0.25 in. wg for ENERGY STAR® fans. This testing is conducted using an ideal installation scenario, which results in performance ratings that may not accurately reflect the actual static pressure levels found in real-world installations. In some cases, this discrepancy between testing in ideal situations and evaluation in real-world scenarios can result in the fan’s failure to meet code.

When specifying bathroom exhaust fans, care should be taken to schedule accurate static pressures based on known length to termination and termination type, a potential oversight that can result in failure to meet code compliance. A well-drawn detail on the drawings giving clear direction on the ducting requirements will further protect the design intent and reduce the possibility of faulty installation.

Code-Compliant-Verified Solutions

Greenheck ceiling exhaust fans have been designed, tested, and certified to perform at 0.40 in. wg, exceeding ENERGY STAR® requirements, and delivering the airflow needed in common installation scenarios to meet today’s stringent codes and eliminate costly callbacks. The fans are powered by an electronically commutated (EC) motor with constant CFM adaptive, variable speed technology programmed to overcome increased static pressure by increasing speed to ensure the fan maintains the installation’s airflow requirements.

Demand-Controlled Whole-House Ventilation

The most advanced ventilation fan on the market, Greenheck’s SP-AP fans include plug-and-play sensor options (humidity, motion, and CO2), 50-80-110 high-speed airflow settings, and 0-60 minute time delay. The EC motor can be controlled with a built-in Precision Airflow Selector, which allows you to dial in the airflow required to match your design or code requirements. SP-AP fans are compatible with Greenheck CRD-300WT UL 263-certified Ceiling Radiation Dampers, a critical safety component in wood-framed multifamily buildings. Available in lighted and non-lighted models.

Greenheck SP-AP0511W-1

Low-Profile Local Exhaust or Whole-House Ventilation

The SP-LP series is one of the most powerful low-profile fans on the market, featuring airflow up to 110 cfm. With a 3-1/2” housing depth, the low profile is ideal for wall or ceiling installations, fitting easily into a 2x4 stud bay. An integrated humidity sensor and two-speed operation upgrades are available. SP-LP fans are also compatible with Greenheck CRD-300WT UL 263-certified Ceiling Radiation Dampers. Available in lighted and non-lighted models.

For more information on Greenheck ceiling exhaust fans, click here or contact your nearby Greenheck representative.