BTU Radiator Sizing - Does size reallllly matter..?

Hi Guys,

I just wanted some advice asap if we can.

Today i have taken my order from Plumb base ready for my plumber to start work Sat morning... The rads all look very small to what i was expecting.

All rooms have been measured correctly and to their furthest points (into the back of fitted wardrobes and alcoves etc) and we have used the BTU Calculators to give us the figures and bought rads that were a little higher than required.

Rads are all Quinn Warmstyle, for the smallest bedroom for eg:
W 2.7
L 4.4
H 2.4

a W and L wall are external with cavity insulation and a single DG window, uninstalled garage below and loft space above with 100mm or more insulation (will be more when i top it up)

I work out that we need 3557 BTU (at calc set to warm and 3222 at normal) and so we have a Quinn Warmastyle Radiator White Single Convcector Radiator 600mm X 1100mm Q11611CW
that on spec produces... Oh, as it happens these are under specced, we was basing the figures off Purmo rads but was told they dont have stock and these are the same... none the less, the output of the above rad is 3355.

My Question is this, do i trust these figures and work my rads out to close to the BTU requirements or over size my rads? we like to feel warm but also like to save money.

My worry is that in my last house it was always so damn cold and now that we have the chance to do it all right with a complete new system, we want it to be spot on.

Why did you not let your plumber do the heat loss calculation, some of the online calcs are not accurate.

You need to calculate heat loss through floors, walls, ceilings, windows, doors.
Also need to consider temperature differentials and air change.

Hi this is one of those threads that can run and run because everyone has their own take on it.

In theory with a condensing boiler the rads need to be quite well sized so the system stays on for long periods and does not cycle on and off as the most efficient use is to have the boiler running at optimum temperature almost constantly to condense fully. The temperatures that the Eco boffins say are comfortable are quite low for me and the Mrs so the stat is often cranked up higher than the 70deg or whatever it is supposed to be.
My personal home choice is slightly over size and rely on thermostatic valves to deal with any rooms that are too hot, which also gives a quicker warm up, but let's see what others think eh!

If you over-size the radiators you can run the boiler at a lower temperature to achieve the required heat and hence have a better chance of it condensing whilst also losing less heat to pipeways etc. All assuming of course that your boiler has a modulating burner control system.

Thanks all.

Anymore thoughts

boiler is a Vaillant 624 System

Over size and use rads that best fit available spaces - I know it's old fashioned but a single panel is more efficient than a double - but people don't like whole walls covered in rads

Nige F said:

a single panel is more efficient than a double.

Click to expand...

Why is that?

How do you define "efficient"?

I'd always oversize if you can fit it into the space with it still looking good. It's great to have the house heat up nice and quickly when you get in.

And double panel will shed a lot more heat a lot more quickly so is worth it.

In my house, with big radiators I leave the heating off until I am 30 mins from home. I turn the heating on from my phone when I'm at the station and by the time I get home the house is roasty toasty. I'm saving money by not having to have the heating on until I need it.

Thanks captains! i think i will get these rads swapped over then. rather the house be over supplied and use TRV's if needed rather than having the heating on for yonks to keep it warm.