Five homes were tested by tracer gas and blower door to assess infiltration caused by leaks in air distribution systems. These homes are not a random sample and therefore may not give an accurate representation of Florida housing. Techniques used to determine the amount of return leak and the amount of infiltration caused by duct leaks are described.

Average infiltration with the air handler running was 1.42 air changes per hour (ach), while with the air handler off, it averaged only O. 14 ach, The infiltration rate with the air handler running is equivalent to an average 290 cubic feet per minute (cfm) (0.1369 m³/sec). Return leaks much larger than supply leaks in all five homes. The return leak fraction averaged 21.6%, or an average of 263 cfm (0.142 m³/sec). Blower door tests found average air changes per hour at 0.20 in H₂0 (50 pascals [Pa]) (ach50) to be 11.79 and the duct system represented 19 of the total leak area in three houses.

Return plenums were repaired and the tests were repeated. Infiltration with the air handler on dropped from 1.42 ach to 0.31 ach. The return leak fraction dropped from 21.6% to 2.6%. Duct system ELA was determinedfor only three homes. While only 43% of the duct leak area or 8% of the house ELA was sealed, the reduction in infiltration when the air handler was running was nearly 80%.

After the repairs were made, tests were performed to assess the impact of closing interior doors on the infiltration rate of the home. When the interior doors were closed, and the air handler was running, infiltration jumped from an average 0.31 ach to 0.91 ach.