Wattage Calculation Formulas
Wattage Calculation Data
Basic Heat Formulas
The following formulae can be employed in determining wattage capacity
required for different materials.
Formula A: Wattage required for heat-up =
Weight of material (lbs) x Specific Heat x Temperature Rise°F
3.412 x Time (hours of fraction thereof)
For specific heat and weights of each material
being heated, see -
Formula B: Wattage
losses at operating temperature = Wattage loss/sq.ft. x Area in sq.ft.
See curves - Guide for Heat Losses
Formula C: Wattage for
melting or vaporizing =
Weight of material (lbs) x Heat of fusion or vaporization (BTU/lb)
3.412 x Heat-up time (hours of fraction thereof)
When the specific heat of a material changes at
some temperature during the heat-up, due to melting (fusion) or evaporation
(vaporation),perform Formula A for heat absorbed from the initial temperature up to the
temperature at the point of change, add Formula B, then repeat Formula A for heat absorbed
from the point of change to the final operating temperature. For heats of fusion and
vaporization and temperatures at which these changes in state occur see Tables 1, 2 and 3 as refered to under Formula A.
For specific applications, substitute the Basic Heat Formulas (A, B, or C above) into the
To Heat Liquids
Wattage for initial heat-up = (a) + (b)
Wattage for operating requirements = (a)
for new material added + (b)
To insure adequate capacity, add 20% to final wattage figures. This will compensate for
added heat losses not readily computed.
To Melt Soft Metals
Wattage for initial heat-up = (a) to melting point + (c) to melt (a) to
heat above melting point + (b)
Wattage for operating requirements = [(a) to
melting point = (c) to melt + (a) to heat above melting point] for added material + 11. To
insure adequate capacity, add 20% to final wattage figures. This will compensate for added
heat losses not readily computed.
To Heat Ovens
Wattage = (a) (for air) + (a) (all material introduced into oven) + (b)
Add 25% to cover door heat losses
Forced Air Heating
Wattage = C.F.M. x temperature rise (°F)
Problem 1: Basic Heating and Heat Loss.
Problem 2: Paraffin melting