Radiator types

1 How the number works

The European radiator maker Kermi explains the convention. The type refers to depth, with the first number counting water-conducting heating plates and the second counting convector plates¹. A UK range from the maker Myson is listed in Type 11, Type 21 and Type 22 profiles, using the same labels³.

Vaillant describes the parts in plainer terms. The panel is the radiator itself and the convector is the row of fins on the back, and it notes that older radiators might have no convector at all².

This table applies Kermi's rule to the three types in Myson's range¹³. No figure comparing the output of each type was read from a page that could be checked, so none is given here.

2 Other kinds of radiator

Vaillant's glossary says sectional radiators are the original form and are now only found in old buildings, and that tubular radiators followed them, also serving as towel dryers⁴. Baxi points out that a heated towel rail is often the highest radiator in a system, so air may collect there first⁵.

Material matters for corrosion. Ideal says aluminium radiators do not suffer iron oxide sludge if there is no steel in the system⁶.

3 Replacing a radiator

Vaillant says to match the number of panels and convectors for a direct replacement, as the wrong choice could leave a radiator unable to heat the room. It also says to keep the same pipe centres, because moving pipes is difficult, and it generally does not recommend changing radiators without a reason, as that disrupts the system².

GOV.UK says adding extra radiators may need building regulations approval⁷. Afterwards the system will need balancing again, which Viessmann says must always follow work on the system⁸.

4 Radiator size and lower temperatures

Lower running temperatures can call for bigger radiators. England's Approved Document L sets a 55 °C flow temperature design limit for new or fully replaced wet systems, and it names too little room for larger radiators as a reason that limit may not be feasible⁹. A boiler swap that keeps the old radiators sits outside that paragraph.