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Best position for a radiator

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Best position for a radiator

Postby Henry » Sat Mar 05, 2011 10:20 pm

Hi,

What's the best position in a room for a radiator? I.e. on an external wall, under a window, away from these areas etc? Also how come you never see several small radiators in a room instead of one big one. Wouldn't this heat a room more evenly?

Thanks

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Re: Best position for a radiator

Postby WELSHMAN » Sun Mar 06, 2011 12:08 am

This is a really good question. When I studied environmental studies I was taught that the radiator should always be fixed to an internal wall, this to aid heating the next room. In reality the radiator is usually fixed to an external wall to help reduce damp, more often than not underneath a window, of which would be the least efficient place to put a radiator. I will be interested to read comments on this.
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Re: Best position for a radiator

Postby Angib » Sun Mar 06, 2011 12:15 pm

The traditional place to put radiators was under windows, at least until the 70s/80s. The logic was that rising column of hot air coming off the radiator would counteract the falling stream of cool air cooled by the (of course, then single-glazed) window. The worst place was considered to be opposite the window where the rising column over the radator and across the ceiling would combine with the falling stream down the window and across the floor to create a continuous air loop - meaning those sitting in the room would be in A Cold Draught (a much-feared condition that at the very least gave you continuous colds and in the elderly caused instant death).

Then the heating engineer's fashion (and that's what much of this really is) swung to compact heating systems - this was said to be to minimise water volume to give quick heat-up but I think it was no coincidence that it also reduced installation costs and so increased profits. This was the advice when I installed my central heating system and I have several rooms with radiators opposite windows. I've never noticed this dreaded draught. Indeed I suspect it may be a good idea to set up an air circulation in rooms so that all parts of the room reach a fairly even temperature - static air means that it will be hotter near the ceiling and cooler near the floor, where the people are, so the room will have to be heated more to achieve the same level of comfort.

I often see big rooms with two radiators though I suspect this is because they couldn't get one radiator big enough for the heat loss. But I've never seen the two radiators next to each other and they are usually on different walls. The one big radiator versus several small ones issue is probably down to installation cost, though tradition will no doubt come in to it too.

The 'best' location will depend on many factors - and in reality things like room layout will be at least as important as heating efficiency. The idea of putting radiators on internal walls "to aid heating the next room" seems a bit cock-eyed as the next room will presumably have its own radiator. More likely putting radiator on internal walls might be proposed for old houses so that the heat wasn't transmitted straight into an external wall and partly lost - though nowadays you would add a radiator reflector panel so at least the radiated heat (ie, not the convected heat) was reflected back into the room. In a modern highly-insulated house, I doubt it matters at all where the radiators are placed.
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Re: Best position for a radiator

Postby WELSHMAN » Sun Mar 06, 2011 1:36 pm

Angib wrote:The idea of putting radiators on internal walls "to aid heating the next room" seems a bit cock-eyed as the next room will presumably have its own radiator.

I think the general idea was that it was better to aid heating the next room then loose the heat through an external wall, sorry for not spelling that out!
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Re: Best position for a radiator

Postby nrg-steve » Sun Mar 06, 2011 3:59 pm

Radiators are usually positioned below windows because this helps offset the radiation losses to the cooler window surface and the cold downdraught from the window. The warm air convection current rising up from the radiator should be directed AWAY from the window surface by a radiator shelf. A clearance of at least 25mm but ideally 50mm should be left between the wall and the radiator.

Water connections to the radiator would ideally be made with the flow to the top header and the outflow to the bottom header at the opposite end of the radiator. This enables the hot water to flow uniformly through all the vertical channels.

Metallic paint, such as aluminium or bronze, can reduce heat output by 10 and 25% whereas ordinary or enamel paint will not affect heat output.

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Re: Best position for a radiator

Postby Henry » Sun Mar 06, 2011 6:07 pm

Some interesting points, thanks guys. So do we think then that in a room with two windows, having two small radiators would be any better (or significantly better) than having one large one?

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Re: Best position for a radiator

Postby nrg-steve » Sun Mar 06, 2011 6:56 pm

Not always easy to give definitive yes or no answers as it will depend on size of room and the sizes of the windows; but it could be better to have two radiators. However this would cost more to install - with two single rads rather than one double rad.

However, in my sitting room there is one large window and on another aspect there are two smaller windows. In this situation it makes sense just to have one rad under the main window.

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Re: Best position for a radiator

Postby Colin S-C » Sun Mar 06, 2011 7:25 pm

Surely these days it depends on the quality of the window, while they will always be cold spots relative to walls,new windows are far superior in retaining heat compared to only a few years ago!
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Re: Best position for a radiator

Postby nrg-steve » Sun Mar 06, 2011 10:15 pm

depends on the quality of the window


Yes, a modern double glazed window has a much better U value than a single glazed window. It is though relatively a big heat loss spot compared to the U value of a modern wall.

The U value of a single pane window is 5.6. Double glazing with ordinary glass has a U value of 2.8 while double glazing with a low E coating has a U value of about 1.9

Compare this with a modern wall which would have a U value of about 0.30 ; much better than 1.9

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Re: Best position for a radiator

Postby Angib » Sun Mar 06, 2011 10:24 pm

On the other hand, I have a few new windows in my solid-brick Edwardian house - the e-glass windows probably have a U-value of 2.0 while the solid brick walls around them are marginally worse at about 2.1!
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