@RedMango,

Yes it means rads larger than current heat loss calcs would prescribe.

Radiator sizing apps, catalogues and charts currently use a 50° deltaT (difference in temperature) between the desired room temperature and the mean (average) water temperature in the radiator.

This is based on gas boiler having a flow temp of 80° and a return temp of 60° (20°deltaT).

1. water entering rad = 80°

2. Leaving rad = 60°

3. Mean water temp in rad = 70°

4. Desired room temp = 20°

5. DeltaT between 3 & 4 above = 50°

To make better use of condensing boilers and reduce energy wastage / burning of gas, green issues, through partL building regs, aims to lower the flow temps of boilers to 55° with a return temp of 35°.

Using the method above (1-5) gives a result thus...

5. DeltaT = 25°

Which is half of what radiators are currently designed and sold at.

In simple terms you do a heat loss calc for a room, choose a rad that has the appropriate KW output for that room (which will be based on a deltaT of 50°) then you double the KW output and make a new selection from the catalogue based on that, to see what dimensions/type of rad will deliver that output, thus heating the space to the desired temp using the lower flow temp of 55°.

As for whether you need to comply or not, it would be in your best interest to do so now, during this opportunity of a new install, because in @10 years time (sooner if law changes) you will need a new heat source in your forever home and by then, it's pretty certain you will not be able to achieve flow temps of more than 55°, thus rendering your heating system insufficient.