Must radiators be bottom fed?

Must radiators be bottom fed? I want to fit a tall, slim radiator in my bathroom, almost the full height of the wall, and the only way to get the pipes to it is through the ceiling, so it would be mounted upside- down.
Running on a Worcester Junior 28i combi, pressurised system, if it makes any difference.
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Hot water tends to rise. If your entry and exit pipes are both at the top you'll get a shallow flow of hot water across the top and most of the radiator will be full of cold water.
You would probably be able to get away with letting the hot water in at the top and having the exit valve at the bottom, but I doubt you'd find a suitable radiator anywhere off the shelf.
Suggest that as far as poss you bring your pipes down in a corner of the room, along to the Rad, through the Rad, back to the same corner and back up beside the in-pipe. Personally I'd insulate both pipes - it's the radiator's job to release heat in the right places, not the pipes. And any pipes in the roof space should be double and triple insulated with an extra layer of insulation on top. Then buried in more insulation.
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On Sun, 03 Feb 2008 00:37:33 +0000, OG wrote:

Nonsense, most compact rads have tappings at all four corners.
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Fair enough .
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The modern roll top rads do not.
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The best way to do it, but a bit involved, is to run soft copper pipe from the tapping to the bottom of the rad. Don't use a lockshield valve, use chrome 15mm joints. Use a 15mm to 8mm reducer and file the pipe stop out. Run the 8mm soft copper through and solder up. The 8mm pipe should be on the flow. Hot in the bottom and cold out the top, then better heat transfer thropugh tall rad. You don't want hot water at the top all the time as all it will do is heat the air near the ceiling.
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Doctor Drivel wrote:

That's a good idea. Actually sounds a bit like some of those rads with a single feed at one corner. My mother-in-law has them; one failure mode is for the internal pipe to drop off...
However, as for the efficiency - if the rad is hottest at the bottom, the hot air from there will rise up and the warmish water at the top will be in warmish air, and there will be very little heat transfer. If OTOH the hot is pushed downwards, the warmish bit will meet cold air and work reasonably well, while the hot bit will meet warmish air and also work reasonably well. This is counter-current heat transfer.
I wrote the above before looking up
http://en.wikipedia.org/wiki/Countercurrent_exchange
Andy
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Radiators don't work quite like that. With a bottom feed the general temperature drop is still from the top to the bottom. Even at the bottom feed end you are unlikely to get a significant drop from bottom to top as the ascending column is much narrower than the descending column.
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Because they were a type of rubber instead of soft copper. The one end valves were great and if copper inserts are far better and one on each end.
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It doesn't matter if the hot enters top or bottom, but the return must be from the bottom or most of the radiator will remain cold.
Radiators are available with connectors top and bottom, unless you have a particular designer one in mind. You can run the pipes down the wall behind the radiator to hide them.
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Andrew Gabriel
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wrote:

You must have the Return from the bottom UNLESS the rad has a baffle inside it that forces the water down and then up the other side. Unlikely but it might be worth a look.
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Can't you run the pipes down the back of the rad and bring them out to the sides? It'd probably look neater as well.

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Clint Sharp

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