Advice · 4 min read · Updated 6 November 2026
8 mistakes people make when buying radiators online
Mistake 1: measuring the wrong thing
Radiators are sold by their body size, height and length, but the measurement that decides whether a straight swap works is the pipe centres. For a standard panel radiator with valves at each end, this is the distance between the centres of the two pipes coming up from the floor or out of the wall. Measure this and the height of the pipes from the floor before you order.
Standard panel radiator lengths step up in 100mm increments, but pipe centres for valves at each end are usually the radiator length plus around 50mm to 70mm, depending on the valves and fittings. If your existing centres do not match any standard size, an installer can usually bridge a small gap with offset valves or extended tails, but a big difference means moving pipes.
Some radiators have valve tappings underneath, in the middle or on one side. If the new radiator's connections are in a different place, pipework will need altering.
Mistake 2: comparing outputs at different Delta T
Radiator outputs are tested at a specific temperature difference between the water and the room. The European standard figure is Delta T50. Some retailers quote Delta T60, which gives a higher number for exactly the same radiator. Always compare like with like.
| Rating quoted | Effect on the stated output |
|---|---|
| Delta T50 | Standard figure for comparison |
| Delta T60 | Roughly 20 to 25% higher than Delta T50 |
| Delta T30 | Roughly half the Delta T50 figure, relevant for heat pumps |
A radiator that looks like a bargain because of a high output may simply be quoted at Delta T60.
Mistake 3: buying for looks without checking output
Designer, vertical and flat-fronted radiators often give much less heat than a standard double panel radiator of the same size. A slim vertical radiator might look perfect in a living room but be far too small to heat it. Work out the room's heat requirement first, then find a style that meets it.
The same applies to chrome towel rails, which give out noticeably less heat than painted rails of the same size. If a bathroom has no other heat source, a chrome rail chosen purely on looks can leave the room cold. Ask for the output at Delta T50 for the exact finish you are buying, because some retailers only list the output for the white version.
Mistakes 4 to 6: valves, brackets and fittings
- Valves are often sold separately, especially for designer and towel radiators
- Angled, straight and corner valves suit different pipe layouts, check which you need
- Brackets are usually included with panel radiators but not always with designer models
- Blanking plugs and bleed valves may need ordering for some radiators
- Chrome valves on a white radiator may not be what you pictured, check finishes match
If an installer is fitting the radiator, ask what valves and fittings they recommend before ordering. It saves a second trip or a delay on the day.
Also check the valve connection size. Most UK radiators have half-inch BSP tappings and connect to 15mm pipe, but microbore systems use 8mm or 10mm pipe and need matching valves or adaptors. Some European and designer radiators use different connections altogether.
Mistake 7: ignoring weight and wall type
Large double and triple panel radiators, and especially cast iron and column models, can be very heavy when full of water. Plasterboard stud walls may need extra support such as timber noggins or special fixings. Period walls with soft brick may need longer fixings. Some heavy radiators need floor feet as well as wall brackets.
Mistake 8: not checking delivery and damage
Radiators are easily dented and scratched in transit. Inspect them on delivery, before signing if possible, and report damage straight away. Do not throw away packaging until you are sure the radiator is undamaged and the right size. Some retailers will not accept returns once a radiator has been fitted or plumbed in.
Check the returns policy before ordering. Some sellers charge a restocking fee or collection charge, and made-to-order colours or sizes are often non-returnable. If you are not sure about the size, it is safer to confirm measurements with your installer first than to rely on being able to send it back.
A simple pre-order checklist
- Measure pipe centres and pipe height from the floor
- Check the room's heat requirement in watts or BTU
- Compare outputs at Delta T50
- Confirm the connection positions match your pipes
- Order the right valves, brackets and bleed fittings
- Check the weight against your wall type
- Inspect on delivery and keep the packaging
Frequently asked questions
What are radiator pipe centres?
Pipe centres are the distance between the centre of the flow pipe and the centre of the return pipe that connect to the radiator valves. For a like-for-like swap, matching this distance means the new radiator can connect to existing pipework with little or no alteration. Measure from pipe to pipe, not from valve body to valve body.
Should I buy the radiator or let the installer supply it?
Either can work. Buying yourself lets you choose exactly what you want and compare prices, but you carry the risk if the size or fittings are wrong. Letting the installer supply it means they take responsibility for compatibility. If you buy your own, send the installer the model details before ordering so they can check it.
Is a higher BTU radiator always better?
Not always. A radiator that is too large for the room can make it overheat and may waste energy if not controlled by a TRV. It is better to match the output to the room's heat loss, with a modest margin. If you plan to move to a heat pump in future, sizing larger for lower flow temperatures is a sensible exception.
buying radiators common mistakes pipe centres Delta T
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