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102.jpg (3709 bytes)  Fiber Insulated Heater Type RDI

Fiber Insulated Heaters Type RDI combine a heat source with thermal insulation in one convenient package giving furnace designers a lightweight alternative to conventional dense refractory supported heaters. These units are designed to heat furnaces to a maximum temperature of 1300C (2372F) with power densities to 2200 w/ft2. They can also deliver power densities up to 4800 w/ft2 for extended periods at 700C (1292F).

RDI Fiber Insulated Heaters utilize powder metallurgy based, helically wound Fe-Cr-Al coil elements and rigid refractory bonded ceramic fiber insulation. Heating elements are positioned in open grooves in the insulation, allowing it to freely radiate. This minimizes the difference between the element and chamber temperature allowing it to operate at higher temperatures and longer periods than units with fully imbedded heating coils.

Alumina-Silica Insulation Type AXHTM is used to support the coils and insulate the heater. It is 100% organic free and will not smoke or outgas. Low thermal conductivity and mass allows the material to withstand extreme thermal cycling.


Thermal Response

Fiber Insulated Heaters Type RDI, like Type FIH, provide rapid heating while consuming little power. The data shown is for a test furnace composed of a custom cylindrical FIH Heater (6in. ID x 10in. OD x 6in. L, 1200W, 120V)  with 2in. thick Alumina Silica Insulation Type AXL discs on each end.


Safe Operation Zone

Fiber Insulated Heaters Type RDI are designed to operate at power densities up to 2200 watts/ft2 at 1300C. They may, however operate at significantly higher power densities at lower temperatures and still provide long life.



Close up view of two different coils in a flat panel RDI Fiber Insulated Heater. The smaller bottom element delivers ~2200 watts @  while the  larger top element delivers ~6650 watts. Both operate at 480 V.

This full cylinder RDI Heater is 2" ID X 6" OD X 12" long. It supplies ~1200 watts at 240 V and is used inside a rapid cycle Heater Module Type HTMOD operating at 1300C (2372F).


Heating source and primary thermal insulation in low mass furnaces, analytical instruments and industrial process equipment operating to 1300C (2372F).


RDI Fiber Insulated Heaters are produced on a custom basis. Typically they are manufactured to customer specification, but ZIRCAR can design and construct units to satisfy a range of heating needs. 

Standard tolerance as shown for Alumina-Silica Insulation Type AXHTM is generally applied to the insulation and  +/-5% to the element resistance. Type "A" uninsulated double twisted lead wires, 9" long are typically supplied and positioned as indicated.

Flat Panel



N & T = 2" M = 2", T = 1" M = 2"

The following figures show a range of possible heater styles and lead locations.  

FIH Flat Panel Leads

Semicylinder FIH

FIH Cylinders 1

FIH Cylinders 2

Flat panel heaters are typically produced up to 36" wide x 48" long x  6" thick. Custom heaters and shapes smaller than a few cubic inches and larger than several cubic feet have been produced.

Cylindrical heaters typically produced have 1" to 24"ID, 1" to 4" wall thickness and are up to 12" long. Custom cylindrical units and shapes smaller than a few cubic inches, larger than several cubic feet, weighing up to 100 pounds, with IDs of 1/2" to 36", wall thickness of 1/2" to 6" and lengths to 48" can be produced.

Custom panels, cylinders, shapes and preparations are available on request. See Fiber Insulated Heater Type FIH for the range of the shapes and sizes that are possible. Our forming processes, large inventory of custom tooling and state of the art machining techniques allow a wide variety of sizes and shapes to be made. Special geometries such as disks, rings, custom bore (round corner square, hexagonal, oval, etc.) cylinders, staved cylinders, troughs, channel, angle, custom-machined shapes and others can be fabricated. Custom machining, compositional variations and the application of surface rigidizers and hardening agents are available.

Please contact us with your special requirements. We are pleased to contact you if you would like more information or want to discuss custom product availability and pricing. Our Fiber Insulated Heater Questionnaire is an excellent tool to use to convey the requirements of a custom RDI Heater.

To Order

Custom RDI Heaters: specify quantity and description (by supplying drawings, sketches, written descriptions or material specifications).

Copyright 2002 ZIRCAR Ceramics, Inc.