Porous-inlet ventilation systems have been found to give satisfactory results in areas where winter temperatures drop to 0°C and below. An investigation was made on a large model building simulating the humidity and temperature conditions prevailing in animal housing during winter. Flax straw was employed as the material of the porous ceiling, since it is a material readily available in some areas. The ceiling porosity was reduced in various stages by placing perforated panels under the material. Tests were made with the naturally occurring convection, and also, comparative tests were made with an additional circulation fan installed.

The simultaneous heat and moisture transmission characteristics of the porous system were evaluated and compared with a similar but nonporous system.

It was shown that the porous ceiling inlet system performs better in conserving sensible heat than does the similar but nonporous system. The performance with naturally occurring convection is better than with additional forced convection.