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

  • VENTILATION, WHOLE HOUSE STRATEGIES - CONTENTS: Key strategies for whole house ventilation & Fresh Air Intake. How to choose the size & type of whole house ventilation system. Table comparing different house ventilation systems. Removing or keeping out indoor contaminants. Best methods for cleaning & filtering indoor air
  • POST a QUESTION or READ FAQs about how to buy, install, use & maintain a whole house ventilation system & ventilation system impacts on indoor air quality
  • REFERENCES

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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

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).

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.

TABLE 7-1 Whole House Ventilation Strategies

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

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:

  • Size the whole house ventilation system correctly. Oversizing will increase heating and cooling costs.
  • Choose quiet, efficient fans in the house ventilation equipment
  • Keep HVAC or ventilation duct runs as short and straight as possible.
  • Locate fresh air intakes away from pollution sources such as cars, pesticides, and outlets from HVAC equipment or exhaust fans.
  • Seal all ducts and insulate where required. Examples: Insulate intake ducts that run though a hot attic or exhaust ducts that pass through a cold, unheated space.
  • Integrate spot ventilation in bathrooms or provide separately.
  • Use separate spot ventilation in kitchens due to grease.
  • Place supply registers high on walls and away from beds, sofas, chairs, and other places likely to cause occupant discomfort.
  • Keep controls as simple and automatic as possible.
  • Educate homeowners about the system and maintenance requirements.

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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