HVI's Fresh Ideas Home Ventilation & Indoor Air Quality Guide Articles
Continuous Whole-House Ventilation
Fans and heat or energy recovery ventilators work continuously to improve indoor air quality.
In the early 1980s, continuous whole-house ventilation systems were developed to meet the indoor air quality needs of the tight, well-insulated homes being developed at that time. Continuous whole-house ventilation can be provided by single and multiport exhaust and supply fans, balanced ventilators, and heat or energy recovery ventilators (HRVs or ERVs).
One or more fans can be combined to supply fresh air and exhaust stale air to provide a continuous level of general ventilation throughout the home. These fans are typically very quiet (less than 1.5 sones) or are remotely located to reduce the perceived sound level in the home. Sometimes it is possible to upgrade a bathroom exhaust fan to a very quiet fan that operates all the time to provide both local bathroom exhaust and continuous whole house ventilation.
The HVI-Certified Products Directory located on the HVI website provides information on a variety of products that can be used for continuous whole-house ventilation. It is important to choose a system appropriate for your climate. Balanced systems with both supply and exhaust air can generally be used in any climate. Exhaust-only systems are appropriate for temperate to cold climates, while supply-only systems are more appropriate for hot climates.
Heat and energy recovery ventilators
Heat and energy recovery ventilators (HRVs and ERVs) bring in fresh air from the outdoors while exhausting stale air from the home. Both HRVs and ERVs moderate the temperature of the fresh air by conducting heat from one air stream to the other. Additionally, ERVs modify the humidity content of the fresh air through the transfer of water vapor from one air stream to the other. Since HRVs and ERVs combine both exhaust and fresh air intakes, we describe them as balanced systems. The continuous fresh air that is provided conditions and improves the indoor air quality, thus increasing occupant comfort, especially for those who suffer from allergies and respiratory ailments.
How they work
The HRV or ERV is a combination of fans, controls and heat-recovery elements that exhaust stale air from the home, bring fresh air in from outdoors and transfer heat energy from one air stream to the other. A continuously running HRV or ERV provides a steady supply of fresh air to the home, while recovering a portion of the energy normally lost through non-heat-recovery ventilation.
In the winter, heat from the stale exhaust air is captured by the heat recovery core and transferred to the cold incoming air. In the summer, the outgoing, air conditioned exhaust air cools, the incoming air.
HRVs and ERVs filter the fresh outside supply air, minimizing the entry of pollen, dust and insects into the home, and are intended to operate year-round. Models suitable for extremely cold climates are equipped with automatic defrost mechanisms, allowing continuous operation throughout the winter.
HRVs and ERVs are available as stand-alone units with independent ductwork or they may be connected to existing forced-air heating and cooling systems. Properly selected, installed, operated and maintained, an HRV and ERV will:
- Exhaust indoor pollutants and help to maintain good indoor air quality
- Provide a continuous supply of fresh, filtered and tempered outdoor air throughout the home
- Recover heat from the exhaust air in winter
- Control excess indoor humidity when outdoor humidity levels are lower
- Cool incoming air in summer when the house is air-conditioned
- Provide an energy-efficient means for reducing acute indoor air-pollutant problems such as radon, formaldehyde, excess moisture or odors.
ERVs can reduce the moisture content of the fresh incoming air reducing the load on the air-conditioning system.
Many ERVs look and operate very similarly to HRVs. An ERV not only conducts heat but also allows water vapor to pass from one air stream to the other. In cold weather, moisture is transferred from the exhaust air stream to the fresh air stream. In warm, humid summer weather, the ERV transfers moisture from the fresh air stream into the exhaust air stream, which the air conditioner has cooled. In both cases, this moderates the humidity from the extreme levels found outdoors.
Selecting a model
There are many different models of HRVs and ERVs, each with its own advantages and uses. To select the right model for your application, consult HVI's Certified Home Ventilating Products Directory, which contains performance-testing reports for HVI-Certified HRVs and ERVs.
Airflow is an important consideration when selecting an HRV or ERV, as the unit's first function is ventilation. It is critical to select a unit suitable for use in the climate in which it will be installed. In cold climates, the unit's frost protection must be sufficient to ensure that ventilation will continue throughout the winter.
Other factors to consider include sensible heat-recovery efficiency, controls, type of defrost system, and power consumption.
To determine the best choice for your area, contact HVI member companies, which have many years of experience with HRVs and ERVs.
The controls for continuous ventilators range from simple to complex. Controls are available that permit variable ventilation rates, automatic high-speed operation (when bathrooms are in use, for example), automatic operation to control excess humidity, timed or proportional operation, and even air-quality-sensing. HVI member companies can provide detailed information to guide your selection process.