Frequently Asked Questions

1 What does P1, K1, P+, K2 & K3 mean?

P1 also known as Type 10, is a type of radiator with 1 radiator panel and no convection fins.

K1 also known as Type 11, is a type of radiator with 1 radiator panel and 1 set of convection fins.

P+ also known as Type 21, is a type of radiator with 2 radiator panels and 1 set of convection fins.

K2 also known as Type 22, is a type of radiator with 2 radiator panels and 2 sets of convection fins.

K3 also known as Type 33, is a type of radiator with 3 radiator panels and 3 sets of convection fins.

2 When do I need to use Low Surface Temperature radiators?

LST radiators are an ideal choice wherever high efficiency heating is required, yet where safety demands a low surface temperature i.e. where people may injure themselves if left in contact with a standard radiator. The range of Stelrad LST radiators reach a maximum 43°C and are ideal for residential homes, hospitals, schools, nurseries and children’s bedrooms.

3 How do I calculate the heating requirements of a house/room?

It is an important and sometime complex calculation when determining what size radiator is required to heat a room to the correct level. STARS (Stelrad Technical Advanced Radiator System) heatloss calculator offers a simpler way to get sizing of radiators right, first time. Both fabric heat loss and ventilation heat loss is also calculated in order to establish the radiator output and size required.

Stelrad measure output in Btu/hr, British Thermal Unit per hour which is the standard measurement used to state the amount of output of any heat generating device. Heat output can also be measured in Watts, 1 watt is equivalent to 3.412 Btu/hr.

4 Where can I find Stelrad BIM products?

Stelrad has invested in several core ranges designed in the format for Building Information Model (BIM). Specifying Stelrad has never been so easy, simply select the product, drag into your document and drop.

5 How can I order a radiator brochure?

You can download the full Stelrad Radiator book from the downloads page. You can also contact us to request a hard copy brochure.

6 What is your product warranty?

Most horizontal steel panel radiators come with a 10 year warranty; all other radiators have a 5 year warranty. The warranty covers any defect that is attributable to a manufacturing, assembly or material fault, further details available on request.

7 Which radiators come in colour?

Stelrad radiators are available in white as standard with a 60% gloss finish; the white is RAL 9016. RAL is a European wide colour matching system.

Each Stelrad radiator is subjected to a multi stage cleaning process before the paint is applied. This involves several rinsing stages, including an iron phosphate and demineralisation rinse. The first coat of paint is applied by electrophoresis and the radiator is then stoved and cooled. The second powder coat is applied and the radiator goes through a final curing stage. It is then allowed to cool, prior to packaging.

Stelrad also offers specific radiators in a variety of colours. Please note that once ordered, coloured radiators cannot be cancelled.

The colours shown on this website and in the Stelrad Radiator Book are reproduced as accurately as the process will allow and can be made to order on the identified products only. To request a colour chart please email

8 Where can I buy Stelrad Radiators, spare parts and touch up paint from?

Stelrad supplies these products to all major plumbers’ merchants, but are not available to buy direct.

9 Do you bend radiators to fit a room?

Stelrad does not bend radiators, and if this is done your warranty will be invalidated.

10 What does Δt mean and should I use Δt50?

Δt refers to the difference in temperature between the water circulating in the central heating system and that of the ambient temperature. It is important to use the correct Δt when selecting your radiators, as the same radiator will have different outputs at different water temperatures due to the heat source.

Δt50 is the UK standard for domestic gas boilers, however Stelrad also quotes at Δt30 and Δt40 for lower water temperature systems, such as renewable systems.

11 What clearances should I leave around my radiator to ensure maximum efficiency and air flow?

Stelrad recommends clearances of 100mm either side, 50mm above and 150mm minimum from the floor to the base of the radiator. This allows adequate airflow when the radiator is placed on the bracket.

12 Which LSTs come with a TRV and lockshield valve?

The LST Plus Vertical and LST iPlus all come with the TRV and lockshield valve factory fitted, as standard.


13 What does TBOE/BOE mean?

TBOE / BOE refers to which position the pipes are connected to the radiator, OE means opposite end i.e. 1 pipe on each side, TB is top bottom i.e. 1 pipe is connected to the top and 1 to the bottom, B is both pipes connected to the bottom.

14 What pressure are your products tested to?

All models are high pressure tested to withstand 152.3 psi (10.5 bar). Strictly controlled independent laboratory testing ensures that all Stelrad radiators are guaranteed to perform to a maximum working pressure of 116 psi (8 bar) at a maximum temperature of 95°C. All Stelrad radiators conform to BS EN 442 – the European Standard for radiators.

15 What connections do your radiators have?

Each radiator has 4 x 1/2 inch connections as standard. A 3/4 inch valve adaptor is also available, providing a 3/4 inch connector option to the valve without reducing performance. Please note that the Concord and Radical have different connections.

16 What is included in the radiator packaging for installation?

Everything required for installation can be found within each radiator’s packaging. Brackets are of a strong design, with open top and deep slots, which facilitate easy and secure installation. Plastic inserts seat the radiator precisely on the bracket, minimising expansion and contraction noise.

The neat nickel-plated plug and vent provide a watertight joint, whilst complementing the superior finish. To facilitate easy one off replacement, nickel-plated brass extension pieces are also available, complete with sealing washer, in 20mm, 30mm and 40mm options.

17 Which of your products can I fit feet on?

All steel panel type radiators, including Classic Column and Concord have optional feet, however these must be specified when ordering.

18 What tappings options are available for my chosen radiator?

Most radiators have tapping different options.  Please download the piping options sheet for illustrations which demonstrate options for panel type radiators.