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A four-unit prototype heat exchanger was installed and tested in a 12,000-bird commercial broiler house to determine if an improved design of a flat-plate air to air counterflow heat exchanger could increase heat recovery and fuel savings, and improve feed conversion and bird quality. Heat recovery, fuel use, feed conversion and bird quality data were compared to results from previous and continuing studies in original test House #1 with a similar two-unit flat-plate heat exchanger installed in 1983. The prototype 1.22 m x 12.2 m (4 ft x 40 ft) heat exchanger units, utilizing three different variable speed fans, were ceiling mounted along the exhaust fan (rear) wall of the 13 m x 61 m (42 ft x 200 ft) broiler House #4. The heat exchanger surface to floor area ratio is 1:5.8. Heat recovery ratio (HHR) for four test flocks averaged 0.71 with a range of 0.67 to 0.74 for the prototype heat exchanger compared to 0.615 average with a range of 0.61 to 0.62 for the original test house. Calculated heat recovery ranged from 11 073 to 31 151 W (37,791 to 100,776 Btu/h) depending on number of units operating at various airflow rates; yielding an LP-Gas equivalent of 2.04 L to 5.49 L (0.54 gal to 1.45 gal) per hour. LP-Gas used per heating degree day (HDD) averaged 1.61 L/HDD,C (0.236 gal/HDD,F) in the prototype House #4 or 50% less than the original test House #1. Feed conversion was the same in both test houses at 1.85 kg(lb) feed/kg(lb) gain with bird weight of 1.65 kg (3.64 lb) compared to 1.87 kg(lb) feed/kg(lb) gain with bird weight of 1.64 kg (3.62 lb) for 11 control flocks in three other houses. Feed conversion in both test houses for a total of 19 flocks in House #1 and four flocks in House #4 was 1.85 kg(lb) feed/kg(lb) gain compared to 1.90 kg(lb) feed/kg(lb) gain for 32 control flocks in previous years. Bird quality as measured by the processor included percent livability, percent Grade A, condemnations, leukosis, septicemia, tumors, bruises, air sac, contamination, and cadavers. Overall bird quality was higher in the heat recovery houses than the control houses and substantially higher than the U.S. average data for the October 1987 to February 1988 period.