Type 10, 11, 21, 22: what the numbers mean
Every steel panel radiator sold in the UK is described by a two digit type number. The first digit is the number of panels (the flat steel water-filled sheets) and the second digit is the number of convector fin sets (the zig-zag steel welded to the back of the panels that pulls air through and adds heat).
| Type | Also called | Panels | Fin sets | Kartell K-Rad name | Typical use |
|---|---|---|---|---|---|
| Type 10 | Single panel, no convector | 1 | 0 | - | Rarely sold now; very slim but low output |
| Type 11 | Single panel single convector (SPSC) | 1 | 1 | K1 | Bedrooms, hallways, cloakrooms, new builds |
| Type 21 | Double panel single convector, "P+" | 2 | 1 | P+ | Mid-sized rooms where depth matters |
| Type 22 | Double panel double convector (DPDC) | 2 | 2 | K2 | Living rooms, kitchens, older homes, narrow walls |
"Compact" radiators, such as Kartell K-Rad Kompact and Eastbrook Compact, have factory fitted grilles on the top and covers on the sides, so you do not see the fins. That is the standard white radiator most UK homes have.
Type 11 vs 21 vs 22 at the same size
Here is the same 600mm high, 1000mm wide white Kartell K-Rad Kompact radiator in all three types. Outputs are Kartell's published figures at Delta T50, the BS EN 442 rating that matches a modern condensing boiler.
| 600 x 1000mm, white | Type 11 (K1) | Type 21 (P+) | Type 22 (K2) |
|---|---|---|---|
| Heat output, Delta T50 | 950 W / 3,241 BTU | about 1,415 W / 4,830 BTU | 1,835 W / 6,260 BTU |
| Heat output, Delta T60 | 1,217 W / 4,152 BTU | about 1,810 W / 6,190 BTU | 2,350 W / 8,020 BTU |
| Output compared with Type 11 | - | about 49% more | about 93% more |
| Panel depth | about 56mm | about 70mm | about 105mm |
| Guarantee | 10 years | 10 years | 10 years |
| PlumbXtra price | £48.00 | £55.98 | £112.00 |
Two things stand out. A Type 22 gives nearly double the heat of a Type 11 the same size, so it is the way to get more warmth without a bigger radiator. And the Type 21 sits in the middle on output but is about 35mm slimmer than a Type 22, which matters behind curtains, doors and furniture.
What size panel radiator do I need?
Work out the heat the room needs, then pick the type and width that meets or slightly exceeds it. A quick method published by Viessmann UK: room length x width x height in metres, multiplied by 108 for a double glazed bedroom or 135 for a double glazed living room. Allow more for single glazing, north facing rooms or two outside walls.
| Room | Size (m) | Heat needed | Type 11, 600mm high | Type 21, 600mm high | Type 22, 600mm high |
|---|---|---|---|---|---|
| Small bedroom | 3 x 3 x 2.4 | 2,330 BTU | 800mm (2,592) | 500mm (about 2,410) | 400mm (2,504) |
| Hallway | 5 x 1.5 x 2.4 | 1,940 BTU | 600mm (1,944) | 500mm (about 2,410) | 400mm (2,504) |
| Double bedroom | 4 x 3.5 x 2.4 | 3,630 BTU | 1200mm (3,889) | 800mm (about 3,860) | 600mm (3,756) |
| Living room | 4 x 4 x 2.4 | 5,180 BTU | 1600mm (5,185) | 1100mm (about 5,310) | 900mm (5,634) |
| Large living or kitchen diner | 6 x 4 x 2.4 | 7,780 BTU | 2400mm (7,778) | 1800mm (about 8,690) | 1300mm (8,138) |
Outputs in brackets are BTU at Delta T50. Notice how the width shrinks as you go from Type 11 to Type 22: in the living room the same heat needs a 1600mm Type 11 or a 900mm Type 22. In a big room it is often better to split the heat across two radiators on different walls.
Enter the room and we will work out the heat it needs and the narrowest 600mm high Type 11, 21 and 22 that covers it.
Method: room volume x 108 (bedroom) or 135 (living room) BTU per cubic metre for double glazing, as published by Viessmann UK, with uplifts for single glazing and exposed walls. Widths use Kartell K-Rad Kompact 600mm high outputs at Delta T50: Type 11 3,241 BTU and Type 22 6,260 BTU per metre of width (Kartell data); Type 21 about 4,830 BTU per metre (from Kartell's published 600 x 1100mm and 600 x 1300mm outputs). This is a sizing estimate; your installer should confirm with a heat loss calculation.
Type 21 or Type 22: which should I buy?
Type 22 is the most searched panel radiator in the UK (2,900 searches a month against 1,900 for Type 21, Google Keyword Planner) because it gives the most heat from the least wall. Type 21 is the better buy in a few specific cases.
| Type 21 | Type 22 | |
|---|---|---|
| Choose when | The radiator sits behind a door, curtains or furniture and depth is tight; the room is mid-sized; you are replacing a Type 21 like for like | Wall space is short; the room is a living room, kitchen or open plan; the house is older or poorly insulated; you have a heat pump or low temperature system |
| Output, 600 x 1000mm | about 4,830 BTU | 6,260 BTU |
| Depth | about 70mm | about 105mm |
| Price, 600 x 1000mm white | £55.98 | £112.00 |
If the calculator puts you at the top end of a Type 21, buy the Type 22. A slightly oversized radiator heats the room sooner and the thermostatic valve throttles it back; an undersized one never gets the room to temperature.
Replacing an old radiator
- Match height and width first. Compact panel radiators connect at the bottom corners, so a new radiator the same width and height usually lines up closely with your existing valves. Changing width means moving pipework or fitting new valve tails.
- Going from Type 11 to Type 22 in the same space gets you close to double the heat with no change to the width. The radiator sits further off the wall, so check the valves still line up and that curtains and doors clear it.
- Old imperial sizes. Older radiators can be slightly off modern metric sizes. Choose the nearest standard width that fits between your valves, and allow for new tails or extensions.
- Brackets and fixings are supplied with Kartell K-Rad Kompact radiators. Fix into brick, block or timber, never plasterboard alone: a 600 x 1000mm Type 22 weighs about 31kg empty and holds about 6 litres of water.
- Valves are sold separately. If you are swapping the radiator, it is a good time to fit new thermostatic radiator valves.
- Delivery only. We supply radiators for delivery; we do not fit. A like for like swap is a straightforward job for a plumber.
How much do panel radiators cost?
PlumbXtra prices for white Kartell K-Rad Kompact radiators, including VAT, at the time of review. Delivery is calculated at checkout and varies by item and supplier.
| Radiator | Output, Delta T50 | Price |
|---|---|---|
| Type 11, 600 x 400mm | 1,296 BTU | £32.48 |
| Type 11, 600 x 1000mm | 3,241 BTU | £48.00 |
| Type 21, 600 x 400mm | about 1,930 BTU | £36.00 |
| Type 21, 600 x 1000mm | about 4,830 BTU | £55.98 |
| Type 22, 600 x 400mm | 2,504 BTU | £58.60 |
| Type 22, 600 x 600mm | 3,756 BTU | £79.34 |
| Type 22, 600 x 1000mm | 6,260 BTU | £112.00 |
| Type 22, 600 x 1200mm | 7,512 BTU | £135.00 |
| Type 22, 600 x 1400mm | 8,764 BTU | £157.00 |
Want something other than white? Eastbrook Compact panel radiators come in matt anthracite and matt black, from £85.26 for a 600 x 400mm Type 22 in anthracite. Browse all 600mm high radiators or white panel radiators.
Three we recommend most often
Kartell K-Rad Type 22 (K2), 600mm high, white300mm to 3000mm wide. 6,260 BTU at Delta T50 for the 1000mm. The most heat per metre of wall. 10 year guarantee.from £58.60View radiator
Kartell K-Rad Type 21 (P+), 600mm high, white400mm to 2200mm wide. About 4,830 BTU at Delta T50 for the 1000mm, about 35mm slimmer than a Type 22. 10 year guarantee.from £36.00View radiator
Eastbrook Compact Type 22, 600mm high, matt anthracite400mm to 1800mm wide. The standard panel radiator shape in a designer colour. 10 year manufacturer warranty, conditions apply.from £85.26View radiatorCommon questions
Is a Type 22 radiator better than a Type 21?
It gives more heat for its size: about 30% more at 600 x 1000mm (6,260 BTU against about 4,830 BTU at Delta T50). It is also deeper, about 105mm against about 70mm, and costs more. Better depends on the room: Type 22 where you need the heat, Type 21 where you need the slimmer profile.
Can I replace a Type 11 with a Type 22 of the same size?
Yes. With the same height and width, the connections at the bottom corners usually line up closely, so it normally swaps onto the existing valves, sometimes with a small adjustment to the tails because it sits further from the wall. You will get close to double the heat.
What does K1, K2 and P+ mean?
They are Kartell's names for its K-Rad Kompact range: K1 is Type 11, P+ is Type 21 and K2 is Type 22. Other brands use the type numbers or the initials SPSC (single panel single convector) and DPDC (double panel double convector).
Are Type 22 radiators good with a heat pump?
They are the usual choice because they give the most output per metre of wall. Size them for the lower water temperature: at Delta T35 a radiator gives about 63% of its Delta T50 output, and at Delta T30 about half. A room needing 5,000 BTU would need a radiator rated about 8,000 BTU at Delta T50 at Delta T35.
Is a double panel radiator more expensive to run?
No. A radiator only gives out the heat the boiler puts into it, and the thermostatic valve shuts it down once the room is warm. A correctly sized Type 22 does not use meaningfully more energy than a Type 11 heating the same room to the same temperature; it simply gets there more easily.
What guarantee do panel radiators come with?
Kartell K-Rad Kompact radiators carry a 10 year guarantee and are certified to BS EN 442. Eastbrook Compact radiators carry a 10 year manufacturer warranty with conditions. Guarantees cover manufacturing defects and assume the system is correctly inhibited.
Not sure which type or width?
Call our heating team on 01282 429061, Monday to Friday 7:30am to 5pm and Saturday 8am to 2pm. Tell us the room size and the radiator you have now, and we will tell you which one to order.
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