The temperature of air in a tunnel-ventilated house increases as it travels from the inlet to the fans. The increase in air temperature is caused by the addition of heat coming from the building surfaces (i.e., curtain and ceiling) as well as from the birds. How much of a temperature difference a producer will see between the two ends of a tunnel-ventilated house depends on how much heat is added to the air as well as how many fans are operating. For instance, if a house has large birds producin...g a lot of heat and only a few fans are operating, a grower would expect a fairly large temperature difference (ten degrees or more). But, if a producer had small birds producing little heat and all the fans were operating, the temperature difference would be very small, less than a degree or two.