20 BI7LLETIX 891, U. S. DEPARTMENT OE AGRICULTURE. 
temperature, Telocity of air over coils, and steam pressure to be used. 
These being known, the heating surface required to raise the satu- 
rated air from the lowest dew-point temperature to the maximum 
entering air temperature may be determined. To this must be added 
the heating surface required to offset heat losses due to type of con- 
struction, climatic conditions, etc. 
The maximum temperatures desirable in the kiln vary, according 
to the product being dried, from 120° F. for thick, refractory stock to 
180° F. for the more easily seasoned woods. 
Table 2.- — Maximum final temperatures for various species. 
Character of wood. Product and species. 
Maxi- 
mum 
tempera- 
ture. 
Very refractory woods Heavy stock — oak for vehicles 120 
Do ' Ordinary thicknesses — swamp oaks and woods of the same ' 130 
■ : class. 
Eefracrory woods Highland oak and woods of t e same class 145 
Average woods Maple, mahogany, walnut, ash, elm, beech . tupelo, syca- 160 
more, hickory, cherry, redwood, and cypress. 
Easily seasoned woods Birch, gum, chestnut, poplar, basswood, butternut, etc.. 180 
spruce, pine. fir. hemlock, etc. 
1 and 2 inch softwoods Douglas fir, pine, fir, etc 200-230 
Where four kilns or less are installed, sufficient heating surface 
should be provided to heat the kilns to the highest maximum tempera- 
ture suitable for the most easily seasoned woods used by the plant. 
Where more than four kilns are built, it would probably be economical 
to design part of the installation for high temperatures for easily dried 
woods and the rest for low temperatures for slow-drying heavy stock. 
The velocity of the air over the coils, the water sprays being located 
and the water pressure maintained as recommended in this bulletin, 
may be assumed to be about 80 feet per minute at 43 pounds water 
pressure at the spray heads, 
Careful consideration should be given the problem of heat loss, the 
following factors being borne in mind and it being assumed that the 
battery of kilns is built in the open and unprotected by surrounding 
buildings : 
1. A single kiln is exposed on all sides, but in a battery of kilns the 
end compartments have exposure on one side only. 
2. The exposure at the ends of the kilns should be provided for in 
excess of the regular heating coil. 
3. The heat loss through the roof should be provided for by a 
special ceiling coil. 
4. There will be some loss of heat through the floor of the kiln 
below the coils, which must be provided for. 
