Radiator Size?

Fit TRVs set them properly, they will turn down automatically.

 

Over sizing rads isnt a problem, apart from cost, and the visual aspect, on the whole. Obviously this is dependant on the system that you have.
TRV's are a plumbers dream, over size and control via the trv.
You see people will never complain about being to hot.
I spent many a day sizing rads or convectors, when trv's were not about.

 

it better to use single panels where possible because they spread the heat more evenly.

Oversexed rads allow a lower flow temperature and greater condensing efficiency.

Tony

 

Sorry to sound thick but what does that mean?

Radiator outputs depend upon the difference in temperature between the radiator (flow temperature) and room temperature. traditionally this was assumed to be 60C. The output or flow temperature of a boiler was about 86C.

With condensing boilers, they work at greatest efficiency at a much lower flow temperature of 55C. This is probably too low for any radiator system to work so you have to compromise. The compromise is a flow temperature of 75C and a smaller temperature difference of 50C.

If you over rate the radiators then you can drop the thermostat back a bit and the boiler will spend more of its time in condensing mode. Even on a normal boiler dropping the thermostat a bit reduces fuel bills.

The best way to achieve a bigger reduction in flow temperature is to have more radiators but smaller. So instead of just one big one you have two (or three) smaller ones. The sum of these adding up to more than the big one. What this does is couple the thermal energy in the radiators into the room more effectively and allows better comfort at a lower room temperature.

The downside, of course, is more cost, more piping, could be difficult to balance and more wall space taken up with radiators. Since in most houses wall space is often at a premium this option is not often used.