Engineer Talk

Surface Heaters - an Overview

by Jerry Sain

As the name suggests, a surface heater is a device that raises the temperature of a surface. Now in the world of heaters, surface heaters aren’t really very sexy - they often consist of little more than a few pieces of mica and some wire.  But throw in a thermocouple or a diode and some creative geometry, and they can get down-right interesting.  Tutco-Farnam Custom Products creates a vast array of surface heaters serving a multitude of industrial needs.  Surface heaters are generally constructed of flat pieces of mica cut (with a CNC machine) to a specified size and shape and wrapped with resistance ribbon.  The ribbon is selected to produce the wattage and voltage required for the particular application.  The wound core is then ‘sandwiched’ between two (2) mica covers to complete the heater.  Additional pieces of mica are sometimes utilized to mount a thermocouple or to provide additional strength or insulation.  An assembled surface heater is usually less than 0.060” thick.

Sizes and shapes
Surface heaters vary greatly in size - from smaller than 4” X 4” up to as large as a full sheet of mica  (38” X 46”).  Tutco-Farnam produces surface heaters in numerous shapes; most are square or rectangular, but they may be round, or even irregular in shape.  The real beauty of these heaters is that the mica can be cut to any shape required to conform to the surface that the application specifies.  Surface heaters have even been created to line the inside of a cylindrical form by using flexible mica - a surface heater in 3-D, so to speak!  

The lead wires used to connect surface heaters normally exit the heater on the sides, but their placement varies to accommodate the heater application.  Lead wire may exit flat (in the plane of the heater) or perpendicular to it, or at pretty much any orientation that best suits the application.

Common Uses
Tutco-Farnam surface heaters are utilized predominantly in the food service industry and in laboratory uses, but any application that requires a heat source in a limited space may benefit from a surface heater.  In the food service industry these heaters provide concentrated, focused heat for warming plates or heating enclosures.  In laboratories made-to-order heat for hot plates is available in a large variety of sizes and shapes.  Applied to the sidewalls and/or bottom of a container or enclosure, surface heaters will effectively heat the product or material inside.  Another industry application which uses surface heaters almost exclusively is heat transfer presses. 

Electrical Ratings
A wide range of heater ratings are possible with surface heaters.  Most Tutco-Farnam surface heaters are built at 120 or 240 VAC, but heaters as low as 24 volts or as high as 600 volts have been constructed.  It’s even possible to design for DC voltages in a surface heater.  Dual voltage surface heaters are available as well, built with a series/parallel circuit with three leads.  Wattages in surface heaters are as varied as the applications - limited largely by the surface area.  100W - 1500W are available in heaters up to 10” x 10”, and larger surface heaters may produce 4500W, or more.

Heat Distribution
In most surface heaters, the heat is evenly distributed across the mica surface.  However, in some applications the heat concentration is required to be ‘zoned’ into regions of warmer and cooler areas.  For example, a warming shelf with sides exposed to cooling air might need to have more heat concentrated along the sides and less in the middle (where it might over-cook or dry out the food held there).  Tutco-Farnam Custom Products specializes in designing heaters to meet the specific parameters required for any application.

Mounting Considerations
Tutco-Farnam surface heaters can be mounted in any position without adversely affecting the performance of the heater.  When attached they are pressed firmly against the surface they are to heat.  Spaces (air gaps) between the heater and the surface make the heater less effective and can cause hot spots which may result in failure.  The reverse side of the surface heater should be well insulated for optimum efficiency.  It goes without saying that mica supported electrical devices and water are not compatible, so adequate steps are required to keep moisture away from the heater.

Tutco-Farnam Custom Products is proud to provide custom designed surface heaters for a wide variety of applications.  If you have an unusual area, a limited space, or just any surface that you need heated, give us a call.  We’ll be glad to work with you to create a heater of the exact size, shape and rating to fit your specific application.