Are Residential Whole House Mechanical Ventilation Systems Reliable Enough to Mandate Tight Homes?

As residential building codes and above-code programs move toward tighter homes with whole-house mechanical ventilation the reliability and homeowner use of ventilation systems become extremely important. As an example of building code direction and concerns, implementation of the 2014 Florida Building Code requirements for whole-house mechanical ventilation and air tightness testing were delayed by the state legislature. The 2014 Florida Residential Code requires whole-house mechanical ventilation be provided for any home with tested air leakage, expressed in air changes per hour at 50 Pascals (ACH50), of < 5, which is also the air leakage upper limit. Similar requirements from the IBC are being implemented in other states (air tightness requirements are stricter in cooler climates). Thus in most states that have adopted the IBC, new homes will be required to have mechanical ventilation systems. What happens when a system fails? Do occupants repair it? Are failures a common enough problem that this is a concern? If failures are a problem, are there steps code bodies can take to minimize risk to health and safety? Toward answering the above questions the Florida Solar Energy Center (FSEC), a research institute of the University of Central Florida, conducted a 21-home field study investigating the failure rates of whole-house mechanical ventilation systems installed in Florida homes over the last 15 years (12 of the 21 systems were installed in the last 3 years). Researchers conducted a survey to assess homeowner ventilation system awareness and maintenance practices. They also inspected and tested the ventilation system to assess its operational status, level of ventilation provided and likely reason(s) for any issues discovered. Homeowners surveyed felt ventilation was important for health, but many were unaware of how their ventilation system operated. Testing found only three of the 21 study homes (14.3%) had ventilation air flow close to the design level with the type of system specified. In two of these homes, the ventilation systems were turned off by the homeowner, so only one of 21 homes (4.8%) was actually receiving the expected ventilation as found. Only 12 of the 21 homes (57.1%) were found to have ventilation systems capable of operating. Issues identified included failed controllers and dampers, partially disconnected or crushed ducts, dirty filters, and poor outdoor air intake locations. The paper provides a summary of the study findings along with a discussion of the results and recommendations for improving whole-house ventilation system performance and reliability.