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'[EE]:: Why are radiators usually installed below w'
2007\05\22@103210 by Russell McMahon

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A friend asks:

Industry practice is to locate heating radiators (most often fed via a
reticulated hot water system) under windows.

Nobody can tell me why this is done and to my mind it would perhaps be
the
worst place from an energy efficiency point of view although there may
be
other reasons (like reducing convective draughts within the room  -
which
can reduce the apparent temperature by several degrees) why it is a
good
idea.

I would hence appreciate your commentary as to what you would expect
to be
the optimum location for a radiator and why.

Any thoughts?



       Russell

2007\05\22@105023 by Mauricio Jancic

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Cool air is more likely to came from windows since glass has less isolation
than walls. If you stay near a windows in a hot room, you can feel the cool
coming from the window.
This also makes easier to have a uniform temperature across the room instead
of having a hot spot where the radiator is and cool spots near the windows.

Regards,

Mauricio Jancic
Janso Desarrollos
Microchip Design Partner
http://www.janso.com.ar
spam_OUTinfoTakeThisOuTspamjanso.com.ar
(54) 11-4502-2983

> {Original Message removed}

2007\05\22@110357 by M. Adam Davis

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One of the reasons to to prevent condensation on the windows, and
another is to warm the air around the leaky window.

You generally have radiators on the outside walls so the convection
keeps the entire roomful of air at the same temperature.

If you place the radiators on the interior walls then you get an
inversion effect where the hot air rises and stays there, and the cool
air from the outside lays on the floor near the walls.  There is some
movement as the cool air creeps to the radiator, but it's not as fast.

Even if it were faster, there would be a noticeable and significant
difference in temperature closer to the outside than the inside.

-Adam

On 5/22/07, Russell McMahon <.....ruslKILLspamspam@spam@paradise.net.nz> wrote:
{Quote hidden}

> -

2007\05\22@110625 by Pablo Ginhson

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That´s right!, and you can take your hand´s warm looking outside....(better than looking a wall or a picture of your mother-in-law ).

Kind regards

Pablo Ginhson> From: infospamKILLspamjanso.com.ar> To: .....piclistKILLspamspam.....mit.edu> Subject: RE: [EE]:: Why are radiators usually installed below windows.> Date: Tue, 22 May 2007 11:50:02 -0300> > Cool air is more likely to came from windows since glass has less isolation> than walls. If you stay near a windows in a hot room, you can feel the cool> coming from the window.> This also makes easier to have a uniform temperature across the room instead> of having a hot spot where the radiator is and cool spots near the windows.> > Regards,> > Mauricio Jancic> Janso Desarrollos> Microchip Design Partner> http://www.janso.com.ar> EraseMEinfospam_OUTspamTakeThisOuTjanso.com.ar> (54) 11-4502-2983> > > {Original Message removed}

2007\05\22@114835 by Carl Denk

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The heat or cooling supplies to a room are not located on interior walls
since (assuming next room is approximately same temperature) the heat
loss/gain is minimal. That leaves the exterior walls which also are
likely to have the greatest heat/cooling load, and the supplies are
located on the outside wall (where the windows need be also) to minimize
the temperature gradient across the room. For gravity or forced air
systems the return air inlets are placed on the inside wall to create an
airflow across the room, minimizing the temperature difference across
the room. For heating the supplies are generally located low with
gravity (warm air is less dense) helping to prevent a vertical
temperature difference, and cooling supplies located high. But
installation costs generally have one supply for heating and cooling and
can be located high or low, sometimes determined by which is the most
uses heating (up North)or air conditioning (down South) (Northern
Hemisphere)(Southern Hemi people, pleas interchange North and South ) :).

Russell McMahon wrote:
{Quote hidden}

2007\05\22@115827 by Vasile Surducan

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On 5/22/07, Russell McMahon <ruslspamspam_OUTparadise.net.nz> wrote:
{Quote hidden}

Before the heat proof window pan era, locating heating radiators below
windows was a must because it generate a courtain against heat lost on
widows surface.
Such heat air courtains are often used today for very large open doors
(no windows, just the open door).
Now this perspective has changed as long there are available windows
systems with 3 or 5 glasses, with less thermal loss than the wall
itself.

Vasile

2007\05\22@124357 by Steve Smith

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Just a musing (A plumber I aint)

If the cold recalculating air from the window is falling it meets the hot
rising air from the radiator thus generating a circulating and stirring of
the air resulting in a slower moving warm air moving into the room from the
median point between glass and window........

Imagine the radiator on the opposing wall to the window this would be
draughty room as the cold air would fall from the window cut you off at the
ankles run across the room before being heated by the radiator causing the
warming of the air probably resulting in stratification of the still section
within the middle area of the room and a hot top section

Regards Steve

{Original Message removed}

2007\05\22@124651 by Loper, Chris

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Maybe nothing to do with temperature differences or efficiency?
The window already prevents (most) furniture from being placed
in that location.
Putting the radiator somewhere else would reduce usable wall space
again.


> Industry practice is to locate heating radiators (most often fed via a
> reticulated hot water system) under windows.


2007\05\22@131912 by Dr Skip

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I think this is being over-thunked! If not by the window, say on the
other side, you'd have a room that was 50 degrees on one side by the
window (even more leakage in the old days), and 80 degrees + (F) on the
other! Grandma certainly would not have put up with that! She'd tell you
you'd catch a cold right in the living room... ;)

-Skip

2007\05\22@134323 by David Braley

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Here in the US, radiators (heater vents, baseboard heaters, etc) are
located below windows to help prevent the moisture inside the house from
condensing on a cold window. In some parts of the country, it is a code
violation to place the heat source anyplace else.

David

Russell McMahon wrote:
{Quote hidden}

2007\05\22@134432 by Herbert Graf

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On Wed, 2007-05-23 at 02:32 +1200, Russell McMahon wrote:
{Quote hidden}

Same thing is done over here in North America with forced air heating:
the vents are almost always below the windows.

My guess as to the reason is you want the heat source in the coldest
part of the room. The windows are the coldest part of the room, so by
putting the heat source there that area of the room will get a little
more heat, resulting in a more even temperature in the room.

Just a guess.

TTYL

2007\05\22@151817 by Peter P.

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The rule of thumb is to put a convection heater under the largest heat
leak/cooled surface. Simple logic shows that this can lead to zero convection
from the cold source with minimal heat input. Therefore that's the most
efficient place to put the heater. Comfort is another thing. For confort there
will be additional smaller heaters in the room if it is large. Typically a steam
pipe or hot water running at the base (again) of the walls around the room/hall.

But without canceling the cold convection from the major heat leaks there will
always be a cold 'draft' somewhere.

Peter P.


2007\05\22@152517 by Peter P.

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Dr Skip <drskip <at> gmail.com> writes:

> I think this is being over-thunked! If not by the window, say on the
> other side, you'd have a room that was 50 degrees on one side by the
> window (even more leakage in the old days), and 80 degrees + (F) on the
> other! Grandma certainly would not have put up with that! She'd tell you
> you'd catch a cold right in the living room... ;)

And yet ... that's exactly the way things work if all you have is a fireplace or
a simple electric radiator to heat the room with ... Now start thinking about
energy recovery: put a slow windmill between the hot and the cold parts of the
room and use it to charge your cell phone battery ... ;-)

Peter P.



2007\05\22@194751 by Gerhard Fiedler

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Peter P. wrote:

> Dr Skip <drskip <at> gmail.com> writes:
>
>> I think this is being over-thunked! If not by the window, say on the
>> other side, you'd have a room that was 50 degrees on one side by the
>> window (even more leakage in the old days), and 80 degrees + (F) on the
>> other! Grandma certainly would not have put up with that! She'd tell
>> you you'd catch a cold right in the living room... ;)
>
> And yet ... that's exactly the way things work if all you have is a
> fireplace or a simple electric radiator to heat the room with ...

Re fireplace: A fireplace is a completely different type of heat source. It
is usually more a (high temperature) radiation source than a (low
temperature) convection source. That's why, traditionally, the coal and
wood stoves were (and are) not placed on the outside walls, differently
from the low temperature heat elements wrongly called "radiators". (A
better name would be "convectors" :)

(BTW, the open fireplaces that seem to be common in the USA are horribly
inefficient for heating. Of course... that's not their purpose, I presume.
But nevertheless, the principle applies to them just as to much more
efficient wood stoves.)

Re electric "radiator": If this is the type of "radiator" that looks like
the common "radiators" mounted under the windows and that typically is also
a low temperature heater, that is then the place where it should go, too,
for the arguments already presented here.

Gerhard

2007\05\22@213257 by Rich

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Basically, you are correct.  The rapid and extreme temperature changes
introduced at the windows will cause excessive cycling of the thermostat
unless the windows are heated.  Also, the moisture from the warm room air
will condense on the cold windows and drip down onto the frame.  This
condensation is reduced if the windows are kept warmer.  Some homes have
"storm windows" to keep the heat of the inside (room) window from
transferring to the outside air.  The airspace between the windows acts as
an integrator.  This also helps the heater under the inner (room) window to
be more effective.  There are HVAC books that have some rules to work out
heat (Q) for a given room size, configuration and number of windows and
location of heaters.  I have not seen any hard mathematics regarding this,
although there are some formulas for calculating the heat transfer, energy
consumption and stability factors.


{Original Message removed}

2007\05\22@213714 by Rich

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That is correct.  Also temperature cycling and energy consumption are
considerations.  The location of heaters is considered in a broader
strategy.

{Original Message removed}

2007\05\22@224832 by Howard Winter

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Russell,

On Wed, 23 May 2007 02:32:20 +1200, Russell McMahon wrote:

{Quote hidden}

Quite!  This goes back way beyond when people started worrying about efficiency, and were primaruly concerned with comfort - windows (especially
if they aren't double-glazed) have vast heat-conduction compared to walls, so on a cold day the air inside the window cools down dramatically,
causing a cold draft to flow across the room from the window.  By warming up this air you reduce the draft, so it feels much warmer than would be
the case if the radiator is elsewhere.  Anyone who hasn't lived in a drafty house probably underestimates this sort of thing :-)  That's why wing-back
armchairs were developed, to shield the sitter from the draft flowing towards the open fire and up the chimney.

Cheers,


Howard Winter
St.Albans, England


2007\05\22@233734 by Rich

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Hey, I like that about the wing-back armchairs.  I never knew that and it is
pretty interesting that such an approach would be taken.  Rather than
address the source, address the comfort.  :o]
{Original Message removed}

2007\05\23@084117 by Carl Denk

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Google for "Heat Loss Calculation" will find more than a few ways to
calculate the heat gain/loss. Here's one link (I didn't look beyond the
front page) http://www.heatload.com/.

The calculations are based on basic Thermodynamics with input of
temerature difference, area, and "R" value. The R values are from
handbooks, manufacturer's data, etc. The calc can be done by hand and
generally for a moderate sized house will fill one page of paper.
Spreadsheet can make better since can do "what if". Depending on the
detail (just to size equipment, or individual room heating wire, pipe,
duct sizes, etc) might be much less.

Rich wrote:
{Quote hidden}

> {Original Message removed}

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