Whole house ventilation system (C) Daniel FriedmanWhole House Ventilation Design Guide

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Whole house ventilation systems:

This article explains how to design, buy, and use a whole house ventilation system to improve indoor air quality in homes.

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Whole House Ventilation Strategies for Improving Indoor Air Quality

Venmar heat recovery ventilatior installed in a home (C) InspectApedia There are a number of strategies for providing whole-house ventilation, which vary in cost, complexity, and effectiveness. All strategies, however, can be categorized as either exhaust-only, supply-only, or balanced.

Below we provide Table 7-1 - Whole House Ventilation Strategies.

The Venmar HRV heat recovery ventilator shown here is discussed in detail at VENTILATION, BALANCED [Click to enlarge any image]

Guide to Sizing House Ventilation Systems - How Many CFM of Vent Fan Capacity are Needed?

As detailed in Best Practices Guide to Residential Construction:

ASHRAE Standard 62-1989 recommends a minimum ventilation rate in houses of 15 cfm per person, or .35 air changes per hour (ACH), whichever is greater. Based on the ACH method, a three-bedroom house of 1,500 sq ft with 8 ft ceilings would require:

(1,500 x 8) x .85 x .35 / 60 = 60 cfm

Multiplying the volume by .85 accounts for partitions and exterior wall thickness.

Using the per person method and assuming two people in the master bedroom and one in each other bedroom, the rate is also 60 cfm.

The revised ASHRAE standard 62.2, released in 2003, uses the formula of 7.5 cfm per person (based on the number of bedrooms plus one) plus an factor of .01 cfm for each square foot of house area. For example, based on the new ASHRAE standard, the same three-bedroom, 1,500-square-foot house would require:

(7.5 x 4) / (1,500 x .01) = 45 cfm.

As these calculations show, a low ventilation rate is adequate if run on a continuous basis. A higher continuous rate would be advisable for a home with higher-than-average moisture levels or pollutant sources such as smoking. Intermittent ventilation can also work as long as the total daily ventilation rate is equivalent, but is most effective when the system is timed to operate when people are home breathing air and generating pollutants.

A two-speed or variable-speed fan provides flexibility, allowing the ventilation rate to be raised when needed, for example when painting a room or during a party. More important than the precise number of cubic feet per minute, however, is a well-designed system that is quiet, reliable, and low- maintenance, ensuring it will actually be used.

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TABLE 7-1 Whole House Ventilation Strategies

Table of whole house ventilation strategies (C) J Wiley, Steven Bliss

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Installation Tips for Whole House Ventilation Systems

Whole-house ventilation systems should be installed by people familiar with the equipment. Since they normally operate at 100 to 200 cfm rather than the much larger fans found in air handlers, they are less forgiving of errors. Numerous field studies have found heat-recovery ventilators performing poorly due to installation errors and poor maintenance.

For good performance with whole-house ventilation systems, follow these general guidelines:

Watch out: many indoor contaminants are simply too small to see, or are not particles at all but rather gases or chemicals. See ENVIRONMENTAL HAZARDS - INSPECT, TEST, REMEDY for our full list of environmental hazard identification and remedy related to buildings.

-- Adapted with permission from Best Practices Guide to Residential Construction.


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