Calculating radiator size

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slider45

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In the process of redecorating our main bedroom now & replacing the woefully undersized and badly positioned radiator.

Are there any calculator program type things which would help us choose the best size rad for the room?

Very approximately 4m square insulated cavity walls. 2.4m window.
Unheated garage below (insulated bedroom floor). Loft above (insulated loft floor).
Layout as below

bedroom.jpg


Cheers!
 
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Its difficult to imagine any room which is so well insulated that cannot be heated adequately by virtually any size rad!

There are many programs but I would expect that 1.5 kW will be about right.

Its better to use a longer single panel as that spreads out the heat evenly.

Tony
 
You have not really given enough info to work out accuratley.

Assuming your ceiling height is 2.4M and room is 2 x 2 and as it is a bedroom @18C and you have cavity insulation then with
1 outside wall = 560Watts
2 outside walls = 640 Watts

If you do not have cavity insulation then 630 watts and 760 watts respectivley.
 
I'm no expert but looking at the picture I think he meant 4 metres squared (ie 4x4) not 4 sq metres, which might make a diff to gas4you's calculation???

Anyway there's a very rough calculator on B&Q's website which other people have found helpful.

Regards.
 
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gas4you said:
You have not really given enough info to work out accuratley.

Assuming your ceiling height is 2.4M and room is 2 x 2 and as it is a bedroom @18C and you have cavity insulation then with 2 outside walls = 640 Watts
Click to expand...

Apologies - I wasn't expecting to have given enough info firsat time round!

The room is 4m square not 4sq M (ie 4m long by 4m wide).
3 External walls with cavity insulation. Double glazing.

You'd be amazed at how cold it got in there with a double 1.2m long radiator last winter. Radiator was sited by the door on a stud wall separating our ensuite shower cubicle.

I blame it on the drafty garage below. But that'll be fixed by this winter.

So - a single 2m long radiator under the window ...... sound good? Bigger? Her indoors must be kept warm!
 
Agile said:
Its difficult to imagine any room which is so well insulated that cannot be heated adequately by virtually any size rad!
Click to expand...
Well the OP has imagined it, and he's not the "professional" that you are. :rolleyes:

There are many programs but I would expect that 1.5 kW will be about right.
Click to expand...
Is your Wild-Stab-In-The-Dark™ method approved by the IPHE?

Its better to use a longer single panel as that spreads out the heat evenly.
Click to expand...
Except that the mass of air reaching the ceiling, for a given length of rad, will be less with a SC rad. I don't know how you've worked out which is better. Perhaps you haven't, and you're just guessing.
 
calculators I've found online mostly point towards a 6K BTU rating. Though they all seem very superficial.

The only calculator I found which even asked how many external walls I have (3) raised the limit to 10ooo BTUs :eek:

This is all pointing towards a twin radiator something like 2.4m long (same size as window opening).

Stelrad Elite P+ or something along those lines..... Don't need anything 'stylish'!
 
Fabric heat loss = 2.37kW
Ventilation heat loss = 0.259kW

Required heat = 2.6kW

According to my calculations anyway :LOL:
 
Thanks all for pointing out room size correctly. I think I read it too quickly :oops:

Recalculated and for a bedroom temp of 18C it comes out to be 1.7 Kw (Mears calculator) if it is north facing I would add approx 10% ;)
 
slider45 said:
Very approximately 4m square insulated cavity walls. 2.4m window.
Click to expand...

If you require a very approximate size then you can see the replies above but as this subject is often taken very seriously more information is required for a considered opinion. i.e.-

Is the window 2.4sqM or 2.4 W x ? H.
Dbl or Sng glazed.
The internal wall separates what sort of room/space beyond?
4M.sq so is that 2.4M (window wall) x 1.7M? If so what is the length of the internal wall?

This would tell you the heatloss of the room and required heat out put from the radiator, the size, type and position is then your choice.

Regards

now even greener BG
 
slider45 said:
You'd be amazed at how cold it got in there with a double 1.2m long radiator last winter.

So - a single 2m long radiator under the window ...... sound good? Bigger? Her indoors must be kept warm!
Click to expand...

600 x 1200 Stelrad Compact K2 should be more than ample. Based on water temp of 50C this gives just over 2KW. Did your old rad have 2 sets of fins on it or just double panel?

If I was fitting this I would go for the 600 x 1600 P+, even more oversized but cheaper to buy and thinner on the wall. Put it under the window, (natural cold spot) You would also probably need one in en-suite. Unless you have a new condensing boiler you are probably running at around 70C waer temp so this will give even more heat output than quoted.

I allowed for double glazing etc etc. You need to get your insulation and drafts sorted though. Mears is the industry standard for sizing rads and is known to be slightly over generous as well!
 
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