Vertical or Horizontal Rad - which will heat room the best?

T

TotalBanker

Guest
Will a 7000BTU vertical radiator (eg. 2m high x 40 cm wide) heat a 5 x 3 meters room as effectively as a 7000BTU horizontal rad (2 meters wide by 40 cm high)?

Some plumbers and radiator salesmen have told me that a horizontal rad will considerably outperform the vertical in terms of heat transferance to the entire room as, being nearer to the ground, its well placed to exploit the convection currents that will bring heat to the other end of the room (5 meters away..). Other plumbers (and the vertical rad sales man...) are insisting that the BTU value of the rad is the only thing I need to worry about and the vertical versus horizontal is a non consideration.

Who should I believe?

By the way, I will be placing the rad on the 3m non-exterior facing wall (ie The rooms window is on the 5 meter wall at the other end of the room from where I'm planning to put the radiator... ie the radiator will be placed at the naturally warmer end of the room..
 
Rad placed at the warm end of the room will tend to produce more draughts than if place on a cold wall or under a window.
 
eamonn123456 said:
Rad placed at the warm end of the room will tend to produce more draughts than if place on a cold wall or under a window.
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Umm - why? the above does not make sense.

The idea with rads is to maximise convection - the movement of air around a room. By placing a rad in a cold spot and close to the ground (cold air sinks, warm air rises) you maximise this convection, thus heating the room quickly and evenly.

Placing an upright rad in a warm corner minimises convection, which is not particularly effective in terms of heating.
 
EDIT: In case I am not being clear - if you read my previous reply, I don't favour putting the rad in the warm part of the room.

If you put it in the warm side, you are warming the warmest air further which will make it rise (faster).

Meanwhile the coldest air is not getting warmed at the coldest side, so it sinks (faster). You get a faster circulation (draughts) with coldest air moving at floor level. Chilly ankles!

If you heat the coldest air first, you are evening out the temperature across the room. Less temp difference between the coldest air and the warmest air (as you have heated the coldest, and not heated the warmest air).

You still get convection but the temp of the air circulating is less extreme, and AFAIK, the convection flow is slower and steadier.

That's my understanding but am happy to be corrected.
 
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eamonn123456 said:
If you put it in the warm side, you are warming the warmest air further which will make it rise (faster).
Click to expand...

The rate the air will rise at is relative to the difference in temperature, not the absolute temperature.
Leo
 
exactly, well put.

But I am not saying that you have to put the rad in the coldest part, just that it is one consideration.
 

Agree - that's my understanding.

Another thing to note is a rad placed under a window effectively creates a warm air curtain in front of the window and traps cold air in the space above the sill.
 
eamonn123456 said:
exactly, well put.

But I am not saying that you have to put the rad in the coldest part, just that it is one consideration.
Click to expand...

But if the rad is in the coldest part, then the difference in the temp of the rad and the ambient temperature in that area will lead to increased convection currents, and with it more effective heating of the entire space.

If you place a rad on the opposite side, it will pump heat upwards to the ceiling, this will result in cooler air from the cold side being dragged across the room.

It all depends on how much colder the cold side really is, whether it's on an internal or external wall, and on the placement of windows, curtains and other furniture.
Leo
 
Leo said:
But if the rad is in the coldest part, then the difference in the temp of the rad and the ambient temperature in that area will lead to increased convection currents, and with it more effective heating of the entire space.
Click to expand...

I agree as stated that this is the preferred thing to do, but it won't lead to increased (faster) convection currents.

The key thing is that it is best to heat the coldest air in the room, not the warmest air.

If you heat the coldest air you are decreasing the temperature differential between the coldest air and the warmest air in the room.

Hence you decrease the rate (speed) of convection currents, to a nice, non-draughty level, which nonetheless will still heat the whole space in a reasonable time.

If you heat the warmest air, the opposite is true.

You don't have to have fast rate of convection to heat the whole space.

Slow and steady is fine, and less draughty.

If you don't understand my explanation, do a google on it, someone else must surely have explained it better and with diagrams.
 
The reason rads are put under windows is to create circulation, this happens when warm air rises straight up, meets the cold front of the window and then the warm air tumbles/swirls around room hence causing circulation. In theory it is correct, however in my experience long curtains restrict heat output.

To the OP question, I would think if the rads have the same output then its half of one and six of another. Go for the style you like/can afford.
 
Eamon, Leo, Diziet, Davy, Steve,
thanks lads. ye are radiators of knowledge of your subject and convincing convectors of informed opinion. My mind has been changed.... Going to get the plumber to re-quote me to put a horizontal rad under the window. That takes care of the vertical versus horizontal decision for now.

Many thanks,
Paul
 
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