Buying guide
Type 21 vs Type 22 Radiator
Choose Type 21 when a shallower projection matters and its verified output meets the room requirement. Choose Type 22 when more output is needed from a similar wall width and the additional depth fits.
Both normally have two water panels; Type 21 has one convector fin and Type 22 has two.
Calculate the output my room requires
| Feature | Type 21 | Type 22 |
|---|---|---|
| Water panels | Two | Two |
| Convector-fin sets | One | Two |
| Depth | Usually shallower | Usually deeper |
| Output at the same height and width | Lower for comparable models | Higher for comparable models |
| Useful when | Projection and circulation space are tight | Wall width is limited but more output is required |
What the type number means
The first digit represents the number of panels and the second the number of convector-fin sets in the common naming convention.
Product ranges can use extra letters or different casing details, so verify the maker's cross-section rather than relying only on a retailer title.
Output and wall space
The additional convector surface lets a Type 22 deliver more heat from a similar visible width. It may avoid needing a much longer radiator, but it projects farther into the room.
Check skirting, curtains, doors, furniture and the installed valve depth—not just the bare radiator.
Exact output still matters
Type is not a capacity. Height, length, water temperatures and model construction still determine watts.
Purmo's official technical table lists different outputs for Type 21 and Type 22 products at stated temperatures. Compare the exact row that matches the model.
Lower-temperature systems
Extra surface area can help at lower flow temperatures, but a Type 22 label does not guarantee suitability for a heat pump. Apply the manufacturer's lower-temperature output or correction factor, and check pipework and flow.
Energy Saving Trust notes that double or triple panels can increase surface area without necessarily consuming more wall width.
Start with what size radiator do I need?, use the radiator calculator, then read Delta T explained.
Final selection and installation should be checked by a competent heating professional.
Check the installed projection
Retailer dimensions may describe the radiator body without valves, wall brackets or the clearance behind it. Ask for a dimensioned drawing and calculate how far the complete installation reaches into the room.
In a narrow route, behind a door or beside furniture, a few centimetres can change whether Type 22 is practical.
Do not assume that the deeper option is less efficient. Efficiency is not established by panel type alone, and the heating system still supplies the heat.
The useful question is whether the emitter can deliver the required output at the chosen water temperatures while fitting the room and allowing air to circulate.
When Type 21 may suit
- The calculated output is comfortably met at the design Delta T.
- Projection into a walkway or furniture zone is tightly limited.
- A longer wall is available, allowing width rather than depth.
- The exact model, valves and brackets fit the intended position.
When Type 22 may suit
- More verified output is needed from a restricted wall width.
- Lower design temperatures require additional emitter surface.
- The greater depth does not obstruct doors, curtains or furniture.
- Pipework and flow are adequate for the selected emitter.
Cleaning access can also differ because an extra convector creates more internal surface. Check whether the casing or grilles can be removed as the instructions describe and whether the installed position leaves room to do so.
Compare exact products at the same height and length when evaluating the effect of type. If the sizes differ as well, the result reflects several changes, not simply the move from Type 21 to Type 22.
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