TM 5-852-9/AFR 88-19, Vol. IX
Figure 4-3. Ductwork installed in a cold attic.
during the winter months. Icing and thawing have caused throwaway-type filters to get wet, collapse, and
jam the face and bypass dampers. Filter icing has completely choked off an opening in 8 to 10 hours of
operation.
(4) Insulation of ducts and pipes handling cold air. Pipes and ducts subjected to cold air must be
provided with insulation and sealed at the vapor retarder penetration. The ventilating unit should also be
insulated up to the heating coil, or to a point where a suitable mixed air temperature is achieved. Insulation
should be sufficiently thick to eliminate condensation on the room surface at the duct.
(5) Special ventilation requirements.
relative humidity should be between 30 and 40 percent. In cold weather, the outside air tends to be very dry
and cold. The use of outside air for ventilation results in the loss of heat and humidity, both of which must
be replaced to maintain healthy and comfortable living spaces. In very cold weather humidifiers may be
required to maintain humidity at acceptable levels. On the other hand, troops hanging large quantities of wet
clothes tend to provide temporary and localized areas of very high humidity which can cause condensation
problems.
4-8
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