How does a Type 21 double panel single convector radiator actually heat a room, and why might it suit a hallway or landing?

Type 21 radiators heat mainly by convection: an internal row of fins warms the air inside the panel and lets that warm air escape through vents at the top. That slimline double-panel with one convector gives a good heat output without a bulky depth, so it's ideal for narrow hallways and landings where you need warmth but have limited wall space. The convector fins boost circulation, so you get quicker room warming than a plain single-panel radiator of the same width.

What size should you pick for your room and how can the BTU filters help?

Use the BTU Output filter to match radiator capacity to your room's heat loss; the site groups outputs from about 1,000–1,999 up to 9,000–9,999 BTU (Delta 50), so pick a range that fits your room. For a small cloakroom or narrow hall you might choose the 1,000–2,000 BTU band and a compact size such as 600 x 400mm, while a medium living room often needs 3,000–6,000 BTU and sizes like 600 x 1200mm or 600 x 1600mm. If you're unsure, check the BTU band first and then select a width and height from the many options available (widths range from about 400mm up to 2,000mm).

Can you use these radiators in tall, narrow spaces or under windows?

Yes. There are horizontal models that suit under-window positions and vertical or horizontal-or-vertical options for tall, narrow walls. Our range includes vertical configurations. Heights range from around 300mm up to 900mm (and some taller models like 2,000mm for special lines), while widths start at roughly 400mm, so you can usually find a slim profile to fit between features or beneath a sill. A 400 x 1400mm or a vertical 450 x 2000mm style can work well where floor-space is tight.

What finishes and styles are available and which will suit a modern or traditional room?

Brands shown include Stelrad, K‑Rad and Solaro, with colour and style choices such as matt black, anthracite and models with a lined cover for a cleaner, decorative face. A matt black or anthracite Type 21 makes a contemporary statement in a modern scheme, while the lined-cover options give a tidier, more finished look that sits well in a traditional hallway. You can also choose from compact ranges (K Rad Kompact) or more premium lines (Stelrad Elite or Solaro P+) depending on the look and budget you want.

Are Type 21 double panel single convectors suitable for larger rooms, or should you look at other types?

Type 21 radiators are optimised for small to medium rooms, giving efficient convection in a slim depth, but very large rooms may need more output than a single convector can provide. If your room needs outputs toward the top of the site's BTU ranges (for example above 6,000 BTU), you can select wider or taller Type 21s, or consider radiators with extra convectors (Type 22 or Type 33) for higher capacities. For instance, a large open-plan living area often benefits from a Type 22 or multiple Type 21s placed around the space to deliver even heat.

Double Panel Plus Radiators - Type 21 (One Internal Convector)

If you have a small to medium room you’d like to heat up, then a double panel single convector radiator is an excellent choice. Convector radiators are slightly different to other radiators in that they don’t solely rely on pipes or tubes, they heat the room by way of convection. The way convector radiators work is that they heat up a row of fins arranged in certain ways inside your radiator, with the fins heating the body of air within the radiator and allowing it to escape through the vents at the top. The slimline design of these radiators is a great option for hallways and landings with its reduced width, without sacrificing the excellent heat output it gives.

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k-rad-kompact-type-21-double-panel-radiator-600-x-1300mm

K Rad Kompact Type 21 600 x 1300mm Radiator - Double Panel Single Convector

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k-rad-kompact-type-21-double-panel-radiator-600-x-1600mm

K Rad Kompact Type 21 600 x 1600mm Radiator - Double Panel Single Convector

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k-rad-kompact-type-21-double-panel-radiator-600-x-1000mm

K Rad Kompact Type 21 600 x 1000mm Radiator - Double Panel Single Convector

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k-rad-kompact-type-21-double-panel-radiator-600-x-1200mm

K Rad Kompact Type 21 600 x 1200mm Radiator - Double Panel Single Convector

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k-rad-kompact-type-21-double-panel-radiator-600-x-1500mm

K Rad Kompact Type 21 600 x 1500mm Radiator - Double Panel Single Convector

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Stelrad LST i Plus P+ Type 21 800 x 650mm Double Panel Radiator Single Convector - 145264

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K Rad Kompact Type 21 600 x 1400mm Radiator - Double Panel Single Convector

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stelrad-compact-p-radiator-450mm-x-2000mm-double-panel-single-convector-143710

Stelrad Compact P+ Type 21 450 x 2000mm Double Panel Radiator Single Convector - 143710

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K Rad Kompact Type 21 400 x 1600mm Radiator - Double Panel Single Convector

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Stelrad Compact P+ Type 21 600 x 2000mm Double Panel Radiator Single Convector - 143776

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K Rad Kompact Type 21 600 x 800mm Radiator - Double Panel Single Convector

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K Rad Kompact Type 21 600 x 500mm Radiator - Double Panel Single Convector

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Stelrad Compact P+ Type 21 600 x 1400mm Double Panel Radiator Single Convector - 143773

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Stelrad Compact P+ Type 21 450 x 1100mm Double Panel Radiator Single Convector - 143705

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Double Panel Plus Radiators - Type 21 (One Internal Convector)

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K Rad Kompact Type 21 600 x 1300mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 600 x 1600mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 600 x 1000mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 600 x 1200mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 600 x 1500mm Radiator - Double Panel Single Convector

Stelrad LST i Plus P+ Type 21 800 x 650mm Double Panel Radiator Single Convector - 145264

K Rad Kompact Type 21 600 x 1400mm Radiator - Double Panel Single Convector

Stelrad Compact P+ Type 21 450 x 2000mm Double Panel Radiator Single Convector - 143710

K Rad Kompact Type 21 400 x 1600mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 900 x 600mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 600 x 600mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 400 x 1400mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 600 x 1100mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 750 x 800mm Radiator - Double Panel Single Convector

Stelrad Compact P+ Type 21 600 x 2000mm Double Panel Radiator Single Convector - 143776

Stelrad Compact P+ Type 21 600 x 700mm Double Panel Radiator Single Convector - 143767

K Rad Kompact Type 21 600 x 700mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 500 x 1200mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 600 x 900mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 600 x 800mm Radiator - Double Panel Single Convector

Stelrad Compact P+ Type 21 450 x 1000mm Double Panel Radiator Single Convector - 143704

Stelrad Compact P+ Type 21 450 x 1400mm Double Panel Radiator Single Convector - 143707

Stelrad Compact P+ Type 21 300 x 2000mm Double Panel Radiator Single Convector - 143659

Stelrad Compact P+ Type 21 450 x 600mm Double Panel Radiator Single Convector - 143700

K Rad Kompact Type 21 600 x 500mm Radiator - Double Panel Single Convector

Stelrad Compact P+ Type 21 600 x 1400mm Double Panel Radiator Single Convector - 143773

Stelrad Compact P+ Type 21 450 x 1100mm Double Panel Radiator Single Convector - 143705

K Rad Kompact Type 21 750 x 500mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 750 x 1000mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 500 x 1400mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 500 x 1600mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 750 x 600mm Radiator - Double Panel Single Convector

K Rad Kompact Type 21 900 x 500mm Radiator - Double Panel Single Convector

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