Bath fans are increasingly asked to perform two functions. They provide spot ventilation, exhausting moist, odor-laden air from bathrooms so that it can be replaced by drier, fresher air from adjoining rooms. They can also provide whole-house ventilation, running round the clock to improve air quality throughout the home. Advanced bath fans incorporate features like multi-speed operation, high-efficiency motors, and built-in sensors that can make them effective in both roles.
Using a bath fan for whole-house ventilation is an “exhaust-only” strategy: the fan pushes stale air out, and outdoor air enters the house through gaps, cracks, and intentional openings. Other strategies are possible. Heat Recovery Ventilators (HRVs) and Energy Recovery Ventilators (ERVs) provide “balanced” ventilation, using fans both to exhaust house air and to bring in outdoor air. Ventilating dehumidifiers are an example of a “supply-only” approach. Outdoor air is drawn in and conditioned under fan power; this forced flow pressurizes the house and increases exfiltration (outward leakage) through gaps and cracks. These different ventilation strategies have been discussed at length on GBA (see Three Ways to Ventilate a Home and Three Types of Ventilation: Pros and Cons). In general, balanced and supply-only strategies provide better control of the source and distribution of fresh air, but at a significant cost in equipment and installation. An exhaust-only approach using a bath fan remains the most affordable—and most common—way to provide whole-house ventilation. (The 2021 International Residential Code (IRC) requires HRVs or ERVs in Climate Zones 7 and 8; in warmer zones, an exhaust-only strategy is allowed.)
Many products on the market
A huge number of bath fan models are available with different price points, airflow rates, and visual styles. Some double as overhead light fixtures, a handy feature, especially in small bathrooms. Bath fans with built-in electric heaters can be a great…
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