Finned tubular heaters — air heating elements for forced and natural convection

Air heaters vs water heaters — watt density limits

Air heaters use the same tubular construction as immersion heaters but operate under a fundamental constraint: air is a poor heat-transfer medium. The maximum safe watt density for a bare heater in forced air is 5–7 W/cm² (32–45 W/in²), compared to up to 15 W/cm² for water. Exceeding this limit causes the sheath to overheat and fail.

Two engineering solutions exist: reduce watt density by making the heater longer, or increase the convective surface area by adding fins — allowing a higher kW rating within the same immersion length.

Bare (unfinned) tubular air heater

A bare air heater is constructed identically to a water heater but rated for air service. It is available in all 10 standard formed shapes — straight, hairpin, L, M, paddle, symmetric double-arm, zigzag, ring, spiral and double-plane hairpin. A threaded fitting can be added for fixed mounting. Non-standard shapes are available to drawing.

Bare air heaters are well suited to ovens, furnaces and drying cabinets where air is contained and flow velocity is low. At higher velocities they are also used in duct heating and air curtains.

Marking example: TEN 215 A 12/3.5 K 220 R22 f4 nM18×1.5 — air heater, M-shape (f4), heated length 215 cm, cold length 40 mm, Ø 12 mm sheath, 3.5 kW, air at 6 m/s, 220 V, bend radius 22 cm, fitting M18×1.5.

Finned tubular heater — construction and performance

A finned heater is designed for rapid heating of large moving air volumes. A continuous metal strip is spiral-wound tightly onto the sheath and furnace brazed, bonding the fins to the sheath for maximum thermal contact. The fins greatly increase the convective surface area in contact with the airflow.

The result: a finned heater can be rated 3–5× higher than a bare tube of the same length. Instead of a 1 kW bare element, a 2–3 kW finned element fits in the same space — the higher surface area keeps sheath temperature within safe limits even at elevated power. Standard fin density is 4–5 fins per inch (FPI); higher density (7–8 FPI) is available for lower sheath temperature requirements.

Marking example: TENR 66 A 13/2.0 O 400 f1 fins 580 — finned heater, heated length 66 cm, cold length 40 mm, carbon steel sheath Ø 13 mm, 2 kW, forced air at 6 m/s, 400 V, straight (f1), fin length 580 mm.

Voltage and power

Any voltage from 12 V to 600 V can be specified, though low voltages limit achievable power due to high current requirements. Standard industrial voltages: 220 V, 230 V, 380 V, 400 V. High-power industrial installations (50 kW+) sometimes use 600 V to reduce cable cross-section.

Available power steps: 100 W increments from 100 W. From 1 kW, 100 W steps. Most common air heater ratings: 0.5 · 1 · 1.5 · 2 · 3 · 5 · 6 · 9 kW.

Sheath materials

Air heater sheaths are typically stainless steel (AISI 304, 430) or carbon steel (C10). Stainless tolerates higher temperatures and moisture. Above 450 °C sheath temperature, Incoloy 800/825 or Inconel 600/625 (stable to 900–1000 °C) are required. Food and pharmaceutical applications require AISI 316L or 321.

Mounting and terminals

Air heaters do not require liquid-tight sealing at the mounting point. A threaded fitting (BSP or metric) is the most practical way to locate a formed heater in equipment. Standard thread sizes:

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

Straight (shape 1) heaters typically do not require a fitting — they are retained by flanges, brackets or welded supports. Terminal options: M4–M6 cold pins (standard); heat-resistant lead wires; quick-connect push-on; flat tab ("flag") terminals for panel mounting.

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.