Ventilation: A Ventilation Guide from HVI - HealthyHouseInstitute.com

When energy was inexpensive, tight houses were rare. Mechanical ventilation systems were not usually necessary except for spot ventilation in bathrooms and kitchens to expel water vapor, odors, fumes, and smoke.

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As homes became tighter to conserve energy, the quality of the indoor air became an increasingly important factor for the health and comfort of the occupants.

Closing the door on the outside world, in effect, closed the occupants into a chamber filled with pollutants, some of which are known carcinogens and many of which are harmful to the occupants over the longterm. Most of these pollutants cannot be seen and many can’t be smelled or sensed naturally by humans.

Bad air has the greatest effect on the youngest occupants and others who are particularly susceptible to the effects of polluted air. Limiting the sources of pollution and controlling ventilation rates are both required to effectively improve the indoor air quality.

HVI supports ventilation rates for indoor air quality (IAQ) based on mechanical ventilation and not reliant upon occupant behavior or natural air flows.

Using ventilation to improve IAQ is a process of dilution, based on the premise that the outdoor air is cleaner than the indoor air. The home’s ventilation system mixes the cleaner outdoor air with the dirtier indoor air, with the more polluted inside air being exhausted to the outside. Because the materials and the occupants in the house continue to add contaminants to the indoor air, the dilution process needs to be continuous to keep the air in the home as clean as possible.

Ideally, the rate of mechanical ventilation will be exactly right to counter the generation of pollutants in the home. Because of the enormous variations in homes, their locations, and how their occupants choose to live, it is difficult to select a uniform ventilation rate that will suit all homes under all conditions.

ASHRAE Standard 62.2-2007 - A Minimum Requirement

HVI recognizes American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Standard 62.2-2007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings, as the U.S. ventilation standard, and the minimum acceptable ventilation rate. This rate takes into account a combination of mechanical fans and air leakage (infiltration) into the home. Infiltration varies from home to home and changes with weather conditions, therefore HVI recommends using mechanical fans (not infiltration) to ensure the minimum ASHRAE ventilation rate.

The ASHRAE Standard 62.2-2007 sets minimum ventilation rates for continuous, whole house ventilation as well as for “spot” ventilation from the bathroom and kitchen. It also addresses many other ventilation issues such as attached garages, transfer air between rooms, filtration and air inlets. The whole building ventilation rate in ASHRAE Standard 62.2-2007 is stated in formulas as 1 cfm (cubic feet per minute) per 100 square feet of floor area plus 7.5 cfm per bedroom, assuming two people in the first bedroom and one person in each additional bedroom. Note that these rates include an “infiltration credit” for ventilation provided by infiltration of 2 cfm/100ft2 of occupiable floor space. As noted earlier, infiltration cannot be relied upon for consistent ventilation rates.

This is calculated as:

Master bedroom = 7.5 cfm x 2
Other bedrooms = 7.5 cfm each
Plus 1 cfm per 100 square feet of home
Sound level: less than or equal to 1.0 sone

Build Tight, Ventilate Right

Building scientists recognized that if a house is built tightly, the rate of ventilation can be more easily controlled, the occupants are more comfortable, and the cost of operating the home decreases.

In addition to whole-house ventilation, HVI recommends the following rates as minimum, intermittent exhaust airflow rates for residential ventilation.

Bathroom:

1 cfm (cubic feet per minute) per square foot for bathrooms up to 100 square feet

For larger bathrooms, HVI recommends sizing the ventilation by the appliances:

Toilet 50 cfm
Shower 50 cfm
Bath Tub 50 cfm
Jetted Tub 100 cfm

Kitchen:

For hoods located against a wall 40 to 100 cfm per linear foot of cooktop
For “island” hoods 50 to 150 cfm per linear foot of cooktop

These are “spot” ventilation rates using ventilation systems that are located at the source of the “pollutant”, like a space suit that treats the air pollutants where they are generated. It is unlikely these fans will be running for hours so their ventilation rates are primarily recommended to remove the pollutants quickly and effectively. To optimize the performance of all fans, HVI recommends designing a duct run as short as possible with a smooth inner surface duct, like galvanized pipe (for remote mounted fans or HRVs/ERVs a section of insulated flexible duct is recommended for preventing transmission of vibrations). Additionally, all exhaust fans must terminate on the outside of the building envelope, and they should be sloped to allow any condensation inside the duct to run to the outside.

Types of Ventilation Systems

Continuous ventilation can be accomplished with mechanical exhaust or supply only, or “balanced” ventilation. In effect, all ventilation systems are “balanced” since the amount of air moving into the house has to equal the amount of air moving out of the house. Balancing the system mechanically assures that the air will come in and go out where it is needed. Tight houses allow for very effective IAQ control. By exhausting air at the source of pollution, the pollutants have the least effect on the overall air in the home. Adding fresh air to bedrooms will help people breathe more comfortably while they are sleeping.

There are three types of integrated, balanced ventilators: Heat Recovery Ventilators (HRV) and Energy Recovery Ventilators (ERV), and Integrated Supply and Exhaust Ventilators (ISEV). An HRV recovers the heat or the cold from the exhaust air stream transferring it to the supply air stream without mixing the two streams. An ERV also recovers the heat or the cold from the exhaust air but it also transfers moisture to the drier air stream. In climates that require a lot of air conditioning an ERV reduces the amount of moisture brought into the house, limiting the air conditioning load. In a heating season, an HRV more effectively reduces moisture in the home. An ISEV will remove indoor air and supply outdoor air, which may be achieved with or without heat or moisture recovery.

Indoor environmental quality includes not only the quality of the air in the home but also the sound levels of mechanical equipment. HVI recognizes that ventilation systems operating at lower sone (a detailed measurement of sound) levels are more likely to be used and improve the quality of the ambient environment.

Other Ventilation Guidelines

There are many new green building initiatives. All of these initiatives have ventilation components, most of them based on ASHRAE 62.2. The U.S. Environmental Protection Agency’s (EPA) Energy Star with Indoor Air Package program is a leader in green building through education, product guidelines and building guidelines. While Energy Star building guidelines may vary by state as the guidelines are adopted by state energy and building programs, Energy Star product guidelines are standard and have become recognized worldwide.

HVI Certification

Energy Star recognizes HVI as the authority on residential ventilation and incorporates the Certified Home Ventilating Products Directory® as the guideline for cfm/watt and sones. The HVI-Certified Ratings Program was created to provide a fair and credible method of comparing ventilation performance of similar products. Not only are products certified, but a random verification program ensures that those products still meet their original performance.

All testing for certification and verification is performed by laboratories independent of any manufacturer. The test standards utilized for testing are, in most cases, developed by HVI using national and international consensus methods. In a few cases, test standards previously developed by other agencies are recognized and adopted by HVI. A complete list of HVI-Certified products and manufacturers can be found in the HVI-Certified Products Directory.

HVI Certification has been accepted and recognized as the method of performance assurance by many agencies including: