Calculating radiator size for awkward room
 

I posted a while ago with requests for help about insulating the sloping
roof of my daughter's bedroom - thanks for all the help: plasterer
finished yesterday and all looks hunky dory (hopefully so will my gas
bill next spring).

Anyway - now I need to install a new, appropriately-sized radiator.
Trouble is I've tried a few "calculators", however they don't cover the
complex shape structure of the room; cross-section looks like this
(except the slopey bits are shallower than this):

________
/ \
/ \
/ \
| |
|____________|

Also there's a dormer window built into one side of the room.

For example:

- The slopey ceiling is made up of 2mm plaster/9mm plasterboard/50mm
polystyrene/50mm Kingspan/0 sarking/clay tiles.

- Flat ceiling is 20mm lath-and-plaster/200mm Rockwool

- Vertical external walls are 2mm plaster/9mm plasterboard/50mm
polystyrene/50mm Kingspan/200mm solid brick

I'm sure your average heating engineer would just eyeball the room and
fit any old rad he knew would be at least OK, however I'd like to get it
reasonably right! How do I go about this?

Thanks
David

Calculating radiator size for awkward room
 

On Thu, 14 Sep 2006 07:08:09 GMT, Lobster
wrote:

|I posted a while ago with requests for help about insulating the sloping
|roof of my daughter's bedroom - thanks for all the help: plasterer
|finished yesterday and all looks hunky dory (hopefully so will my gas
|bill next spring).
|
|Anyway - now I need to install a new, appropriately-sized radiator.
|Trouble is I've tried a few "calculators", however they don't cover the
|complex shape structure of the room; cross-section looks like this
|(except the slopey bits are shallower than this):
|
| ________
| / \
| / \
| / \
| | |
| |____________|
|
|Also there's a dormer window built into one side of the room.
|
|For example:
|
|- The slopey ceiling is made up of 2mm plaster/9mm plasterboard/50mm
|polystyrene/50mm Kingspan/0 sarking/clay tiles.
|
|- Flat ceiling is 20mm lath-and-plaster/200mm Rockwool
|
|- Vertical external walls are 2mm plaster/9mm plasterboard/50mm
|polystyrene/50mm Kingspan/200mm solid brick
|
|I'm sure your average heating engineer would just eyeball the room and
|fit any old rad he knew would be at least OK, however I'd like to get it
|reasonably right! How do I go about this?

Put one twice the size you think would be right, and fit a TRV.
--
Dave Fawthrop dave hyphenologist co uk Google Groups is IME the *worst*
method of accessing usenet. GG subscribers would be well advised get a
newsreader, say Agent, and a newsserver, say news.individual.net. These
will allow them: to see only *new* posts, a killfile, and other goodies.

Calculating radiator size for awkward room
 

On Thu, 14 Sep 2006 07:08:09 +0000, Lobster wrote:

I posted a while ago with requests for help about insulating the sloping
roof of my daughter's bedroom - thanks for all the help: plasterer
finished yesterday and all looks hunky dory (hopefully so will my gas
bill next spring).

Anyway - now I need to install a new, appropriately-sized radiator.
Trouble is I've tried a few "calculators", however they don't cover the
complex shape structure of the room; cross-section looks like this
(except the slopey bits are shallower than this):

________
/ \
/ \
/ \
| |
|____________|

Also there's a dormer window built into one side of the room.

For example:

- The slopey ceiling is made up of 2mm plaster/9mm plasterboard/50mm
polystyrene/50mm Kingspan/0 sarking/clay tiles.

- Flat ceiling is 20mm lath-and-plaster/200mm Rockwool

- Vertical external walls are 2mm plaster/9mm plasterboard/50mm
polystyrene/50mm Kingspan/200mm solid brick

I'm sure your average heating engineer would just eyeball the room and
fit any old rad he knew would be at least OK, however I'd like to get it
reasonably right! How do I go about this?

Thanks
David

You can calculate it by hand (or on a spreadsheet) adding up for each
surface its areas * U value of the material * temperature differnce
across it; then add the volume of the room * no of air changes per hour *
temperature difference (inside - outside) * 0.36.

Calculating radiator size for awkward room
 

- The slopey ceiling is made up of 2mm plaster/9mm plasterboard/50mm
polystyrene/50mm Kingspan/0 sarking/clay tiles.

- Flat ceiling is 20mm lath-and-plaster/200mm Rockwool

- Vertical external walls are 2mm plaster/9mm plasterboard/50mm
polystyrene/50mm Kingspan/200mm solid brick

It won't need a very big one, unless the room is huge. You didn't state
dimensions.

Christian.

Calculating radiator size for awkward room
 

"Dave Fawthrop" wrote

Put one twice the size you think would be right, and fit a TRV.
--
That's pretty much our plumbers strategy. It makes sense to me.

H

Calculating radiator size for awkward room
 

On Thu, 14 Sep 2006 11:02:50 +0100, HLAH wrote:


"Dave Fawthrop" wrote

Put one twice the size you think would be right, and fit a TRV.
--
That's pretty much our plumbers strategy. It makes sense to me.

Price of steel these days it's better to calculate it and get it right.
Often I've been suprised how small (and sometimes how large) a rad needs
to be for a given room.

Calculating radiator size for awkward room
 

Lobster wrote:
I posted a while ago with requests for help about insulating the sloping
roof of my daughter's bedroom - thanks for all the help: plasterer
finished yesterday and all looks hunky dory (hopefully so will my gas
bill next spring).

Anyway - now I need to install a new, appropriately-sized radiator.
Trouble is I've tried a few "calculators", however they don't cover the
complex shape structure of the room; cross-section looks like this
(except the slopey bits are shallower than this):

________
/ \
/ \
/ \
| |
|____________|

Also there's a dormer window built into one side of the room.

For example:

- The slopey ceiling is made up of 2mm plaster/9mm plasterboard/50mm
polystyrene/50mm Kingspan/0 sarking/clay tiles.

- Flat ceiling is 20mm lath-and-plaster/200mm Rockwool

- Vertical external walls are 2mm plaster/9mm plasterboard/50mm
polystyrene/50mm Kingspan/200mm solid brick

I'm sure your average heating engineer would just eyeball the room and
fit any old rad he knew would be at least OK, however I'd like to get it
reasonably right! How do I go about this?


You don't mention size, but what you have is better insulated than most
of my upper rooms and a kilowatt sorts those out.


Thanks
David

Calculating radiator size for awkward room
 

John Stumbles wrote:
On Thu, 14 Sep 2006 11:02:50 +0100, HLAH wrote:


"Dave Fawthrop" wrote

Put one twice the size you think would be right, and fit a TRV.
--
That's pretty much our plumbers strategy. It makes sense to me.

Price of steel these days it's better to calculate it and get it right.
Often I've been suprised how small (and sometimes how large) a rad needs
to be for a given room.

TBH I suspect that the cost difference between my largest
"guesstimated" rad wouldn't be vastly different to the ideal size, so
that's not my main motive - would just rather keep it neat and not clog
up the room with more hardware than required.

Anyone know of a Noddy guide to calculating U-values? Once tried doing
it from first principles before, without a software calculator, and
came unstuck!

For the purpose of rad sizing/U-value calcs, does it matter whether the
sloping area is considered as "wall" or "ceiling"?

(BTW floor area is (IIRC) something like 3.5 x 3m (I'm not at home now)
but the flat area of the ceiling is probably half that?)

Thanks
David

Calculating radiator size for awkward room
 

Lobster wrote:
John Stumbles wrote:
On Thu, 14 Sep 2006 11:02:50 +0100, HLAH wrote:

"Dave Fawthrop" wrote
Put one twice the size you think would be right, and fit a TRV.
--
That's pretty much our plumbers strategy. It makes sense to me.
Price of steel these days it's better to calculate it and get it right.
Often I've been suprised how small (and sometimes how large) a rad needs
to be for a given room.

TBH I suspect that the cost difference between my largest
"guesstimated" rad wouldn't be vastly different to the ideal size, so
that's not my main motive - would just rather keep it neat and not clog
up the room with more hardware than required.

Anyone know of a Noddy guide to calculating U-values? Once tried doing
it from first principles before, without a software calculator, and
came unstuck!

For the purpose of rad sizing/U-value calcs, does it matter whether the
sloping area is considered as "wall" or "ceiling"?

(BTW floor area is (IIRC) something like 3.5 x 3m (I'm not at home now)
but the flat area of the ceiling is probably half that?)


I cvan tell you instantly by comparison with here, that something
around a kilowatt (3500 BTU/h) will be ample. TRV it of course to make
sure you do not overheat.

I have less good insulation and the one room my 1.2KW isn't quite enough
is about 5x3 meters, north facing, with not much heat coming up from
below as its over a guest area thats not in use often.

I'd say one meter length of double radiator would be ample. Or two
smaller if it fits better aesthetically. I hate radiators..I fitted hot
air blowers instead. Yes they whirr, but a kilowatt is a 18" square
panel in the wall..

Anyway, pick whatever suits from e.g. here

http://www.screwfix.com/app/sfd/cat/...01444&ts=37431



Thanks
David

Calculating radiator size for awkward room
 

On Thu, 14 Sep 2006 05:17:55 -0700, Lobster wrote:

TBH I suspect that the cost difference between my largest
"guesstimated" rad wouldn't be vastly different to the ideal size, so
that's not my main motive - would just rather keep it neat and not clog
up the room with more hardware than required.

Anyone know of a Noddy guide to calculating U-values?

Google :-)

There are a few standard U values used in the calculators and you can pick
up some others online

Here are some I made up earlier :-)

Surface Construction U source
Wall Brick 220 + plaster 13 2
Brick 335 + plaster 13 1.6
Block heavy 200 + air 25 + pboard 10 1.8
Block heavy 200 + air 25 + exp poly 25 + pboard 10 0.79
Block light 200 + air 25 + exp poly 25 + pboard 10 0.46
brick + cavity + brick 1.68 Warmfill
brick + cavity + concrete block 1.55 Warmfill
brick + cavity + clinker block 1.4 Warmfill
brick + cavity + insulation block 1.05 Warmfill
brick + bead-filled cavity + brick 0.49 Warmfill
brick + bead-filled cavity + concrete block 0.47 Warmfill
brick + bead-filled cavity + clinker block 0.45 Warmfill
brick + bead-filled cavity + insulation block 0.42 Warmfill

Windows Wooden SG 5
Wood/uPVC DG 2.9
Low-emissivity Double Glazed 1.9 Pilkington 12mm gap, Pilkington 'K' glass
Argon filled/low-e glass DG 1.6 Pilkington
Aluminium, no thermal break, single 6.4
Aluminium, no thermal break, double 4.3
Aluminium, thermal break, single 5.8
Aluminium, thermal break, double 3.7

Floor Suspended, 1 air brick, bare 0.61
Suspended, 1 air brick, covered 0.59
Suspended, 1 air brick, bare 0.82
Suspended, 1 air brick, covered 0.68
Solid on earth 0.36

Roof uninsulated 0.7 guess
fibre 60mm 0.55
fibre 80mm 0.43
fibre 100mm 0.36
fibre 60mm + sarking underlay 0.51
fibre 80mm + sarking underlay 0.4
fibre 100mm + sarking underlay 0.34
fibre 60mm + felt on sarking board 0.48
fibre 80mm + felt on sarking board 0.39
fibre 100mm + felt on sarking board 0.32


For the purpose of rad sizing/U-value calcs, does it matter whether the
sloping area is considered as "wall" or "ceiling"?

Nope

Calculating radiator size for awkward room
 

John Stumbles wrote:
On Thu, 14 Sep 2006 05:17:55 -0700, Lobster wrote:

TBH I suspect that the cost difference between my largest
"guesstimated" rad wouldn't be vastly different to the ideal size, so
that's not my main motive - would just rather keep it neat and not clog
up the room with more hardware than required.

Anyone know of a Noddy guide to calculating U-values?

Google :-)

There are a few standard U values used in the calculators and you can pick
up some others online

Here are some I made up earlier :-)


[snipped U's]

Thanks a lot John - I'll fire up Excel over the weekend and have a play!
David