Type 11, 21, 22 or 33? How to choose steel panel radiator types by heat output, depth and room

What the type numbers actually mean

Every steel panel radiator carries a two-digit type designation: 11, 21, 22, 33 and so on. The digits are not a model code — they describe construction. The first digit is the number of water-carrying panels; the second is the number of convector fin sets (the corrugated steel finning welded to the back of each panel to increase surface area). A Type 22 therefore has two panels and two convector sets; a Type 11 has one panel and one convector; a Type 33 has three panels and three convector sets. More panels and more fins mean more heat-emitting surface packed into the same face dimensions — but also a deeper radiator that sits further off the wall. Understanding this single rule makes radiator selection far more predictable than picking by price or by picture.

Output and depth: the trade-off in one table

For a given height and length, output rises with type but so does depth off the wall. As a rough guide at EN 442 ΔT50 reference conditions, a Type 11 is the slimmest at roughly 55–65 mm deep and the lowest output; a Type 21 adds a second panel behind the first for more output at around 65–80 mm; a Type 22 adds a second convector set for a substantial output increase at around 90–110 mm; and a Type 33 stacks three panels and three convectors for the highest output at around 145–160 mm. The exact figures depend on the manufacturer's tested data, which should always be quoted at ΔT50 so specifications are comparable — see our explanation of EN 442 ΔT50 and ΔT30 for why the reference condition matters when you compare two suppliers.

Matching a type to a room

Start from the room's heat-loss calculation in watts, then read across the manufacturer's output tables to find a radiator whose ΔT50 output meets or slightly exceeds that figure at the height and length that physically fit the wall. Where wall space is generous, a taller or longer Type 11 or 21 keeps the radiator slim and unobtrusive. Where wall space is tight — under a short window, in a hallway, in a bathroom — a Type 22 or 33 delivers the required output in a compact face at the cost of protruding further into the room. For our detailed method on turning heat loss into a radiator size, see calculating radiator output per room. As a rule, prefer the slimmest type that meets the load: deeper radiators cost more, weigh more, and hold more water.

Low-temperature and heat-pump systems change the answer

The type numbers above assume traditional boiler flow temperatures. If the system runs at low temperature — as heat pumps do, typically 35–45 °C flow — the effective ΔT drops well below 50, and every radiator emits far less heat than its ΔT50 rating. In these systems the sizing logic flips toward the higher types: a Type 22 or 33 that would be oversized on a hot boiler becomes the sensible default because it recovers the lost output through sheer surface area. Buyers specifying radiators for heat-pump-ready or renovation projects should size at the actual design ΔT, not the catalogue ΔT50 figure. Our post on low-temperature radiators for heat pumps covers this in depth.

Getting it right at the specification stage

For B2B buyers and project specifiers, the type mix across a building is a procurement decision, not just a technical one. A residential block will typically need a spread of Type 11 through 33 depending on room size and glazing, and it is far cheaper to confirm the mix before production than to swap protruding radiators after handover. When you brief a factory, provide the per-room heat loss and the design flow temperature, and ask for ΔT50 output data plus depth for each proposed type so the fit and the output are both verifiable. Our products page lists the panel ranges available for specification, and our FAQ covers minimum order quantities, lead times and documentation for project orders.

About the manufacturer

Jiuding Radiator (Tianjin Jiuding Sunshine HVAC Equipment Co., Ltd.) is a family-run manufacturer producing steel panel and column/designer radiators in Tianjin, China since 2002, with export to Europe, Russia, and Central Asia. Products hold CE / EN 442 certification (CPR Declaration of Performance assessed by a notified body), ISO 9001 and ISO 14001 certification, and comply with GOST requirements for the Russian market. For wholesale inquiries, specifications, and samples: www.jdradiator.com | lunan@jdradiator.com / kevin@jdradiator.com | +86-22-69189950.