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Technical:  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.

Specific Applications
For specific applications, substitute the Basic Heat Formulas (A, B, or C above) into the following:

To Heat Liquids
Wattage for initial heat-up = (a) + (b)
                                                  2

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)
                                                                                                 2

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)
                                      3

Problem 1:  Basic Heating and Heat Loss.

Problem 2:  Paraffin melting