When helping customers choose their radiators we will often ask ‘How old is the boiler?’. This will quite likely have an impact on the final style and size of the radiator the customer ends up buying. Often the answer is that ‘It is quite old. But runs ok. But we have been told that we need to change it by our plumber/builder’.

Here at The Radiator Centre, we are not fans of getting rid of perfectly good equipment and incurring unnecessary costs, if it can be helped.

In a lot of situations, older boilers can be considered far superior to their modern counterparts. They tend to have thick cast-iron heat exchangers, minimal electronics and few moving parts, save from an external pump. Whereas modern condensing boilers are usually constructed using thin stainless-steel/aluminium heat exchangers and are packed with electronic controls and circuit boards. It is usually the circuit boards where the problems start and if you manage to go longer than 5 years without some expensive repairs you have defied current estimates.

Our advice is to keep existing older boilers regularly serviced and running for as long as possible. Any noticeable fuel savings as a result of installing a modern condensing boiler may well be negated by repair costs and a shorter working-life.

However, when sizing a radiator the age of the boiler does become an important factor.

Boilers pre-2007 will most probably be heating the water to a greater degree resulting in hotter ‘flow’ and ‘return’ temperatures. As you would expect, the more heat that gets put into a radiator, the more heat it emits.

This specification is known as known as DeltaT or ∆t, and represents the correlation between the flow and return temperatures when subtracted from an industry standard room temperature of 20ËšC.  With an older boiler the calculation would be such;

Flow temperature 85ËšC + Return temperature 75ËšC = 150ËšC

160ËšC / 2 = a mean temperature of 80ËšC

Mean temperature 80ËšC minus an average room temperature of 20ËšC

Equals a temperature difference of 60˚C. Or DeltaT 60 (∆t60)

Newer condensing boilers work at their most efficient when operating at DeltaT 50 (∆t50). This is usually calculated in the following way;

Flow temperature 75ËšC + Return temperature 65ËšC = 140ËšC

140ËšC / 2 = a mean temperature of 70ËšC

Mean temperature 70ËšC minus an average room temperature of 20ËšC

Equals a temperature difference of 50˚C. Or DeltaT 50 (∆t50).

A radiator will appear to have a higher output if it is quoted at DeltaT 60, than it would do if quoted at DeltaT 50. It will appear to be more efficient; possibly even smaller than similar styles of radiator as it would suggest it needs less water to generate the necessary heat.

All current heating products should be quoted at DeltaT 50 in line with European regulations on energy conservation. However some manufacturers and merchants still continue to publish old data and you have to ask why. In reality, “If it appears too good to be true, it probably is!”

All the products are displayed with a specific DeltaT figure, so customers have an accurate understanding of what the heat output from a particular radiator is likely to be (for our range of efficiency radiators, we even quote outputs at DeltaT30 to take into consideration more energy-efficient air-source and ground-source heat pumps).

If you have any questions about the specific DeltaT value a product is being quoted at give The Radiator Centre a call and we would be only too happy to help.


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