Water and oil immersion heaters — tubular electric heating elements

What is a tubular immersion heater

A tubular immersion heater (also called a tubular electric heating element or "direct-immersion element") is designed for direct immersion in water, oils, fats and similar liquids. The construction is essentially unchanged since the 1950s and consists of five components:

• Metal sheath tube — copper, stainless steel or carbon steel;
• Resistance wire (nichrome Ni80Cr20 or FeCrAl) — the heat source;
• MgO (magnesium oxide) insulation — compacted powder filling the annular space between wire and sheath, electrically insulating yet thermally conductive;
• Terminal pins (cold ends) — conducting terminal rods exiting from the element ends;
• Ceramic end seals — dielectric closures at the terminal exits.

A threaded fitting (screw plug) or plate flange is added where the element passes through the vessel wall. A screw plug element is the standard choice for domestic and light-commercial boilers; a multi-element flanged assembly for higher powers and industrial tanks.

Water vs oil — watt density limits

Water is the ideal immersion heating medium. It has high thermal conductivity, removes heat from the sheath rapidly, and cannot exceed 100 °C at atmospheric pressure. Watt density can reach 15 W/cm² (97 W/in²) for stainless steel sheaths in clean water.

Oil is fundamentally different. Thermal conductivity is poor. At watt densities above 3 W/cm² (19 W/in²) the oil film at the sheath surface begins to carbonise — the coke layer acts as additional insulation, sheath temperature climbs further, and the element fails. To prevent this, oil heaters are designed at 1.5–3 W/cm² (10–19 W/in²). A higher-power oil heater needs a longer heated length, not a higher watt density — a 4 kW oil heater may exceed 2 m in immersion length.

Voltage and power

Any voltage from 12 V upward can be specified. Standard supply voltages: 110, 220, 230, 380, 400 V; maximum 600 V. Running a heater below its rated voltage reduces power as the square of the voltage ratio — a 2 kW / 220 V element on 110 V delivers only 0.5 kW.

Available power steps: 100 W increments from 100 W (150, 200, 250 W…). From 0.5 kW, 0.1 kW steps. Most common ratings: 0.5 · 1 · 1.2 · 1.5 · 1.7 · 2 · 2.5 · 3 · 4 · 5 kW.

Sheath materials (GOST 13268-88 codes)

Sheath material is selected by medium and temperature. GOST 13268-88 identifies each material/medium combination with a single letter code used in the model number:

Example: TEN 90 A10/1.3 P 230 f7 — code P identifies carbon steel sheath for water (pH 7–9).

Additional materials: AISI 316L, AISI 321 (food and pharmaceutical), Incoloy 800/825 (above 450 °C sheath temperature), titanium and PTFE-coated (aggressive media including acids).

Fittings and terminals

Screw plug (threaded fitting) sizes — sheath diameter determines the maximum available fitting:

• BSP thread: G 1/2", G 3/4", G 1", G 1 1/4", G 1 1/2", G 2"
• Metric thread: M14×1.5, M16×1.5, M18×1.5, M22×1.5, M24, M26, M28

Electrical terminals are M4–M8 threaded cold pins (diameter constrained by sheath size). Additional options: heat-resistant lead wires with sealed junction; quick-connect push-on terminals; flat tab ("flag") terminals.

Note for refrigeration applications: defrost heater wire-to-pin joints must be sealed against condensate — specify "sealed junction" when ordering.

Order worldwide

Custom-manufactured to drawing — from 3 days, from 1 piece. Worldwide shipping via DHL, FedEx, SDEK. 1-year warranty on all products. In business since 2010. To order, Send us a sketch, a photo of an existing heater, or describe your requirements — we will work out the specifications and provide a price within 15 minutes during business hours.

Certification: GOST 13268-88, on request — DIN, IEC, ASTM. TEN-Miass, ul. Shota Rustaveli 82a, Tashkent, Uzbekistan 100000. Phone: +998 50 090 19 24.