On 10 Dec 2005 08:54:02 -0800, Sadly wrote:

Alec wrote:
Morning All. I have a 2m X 6m UPVC conservatory with warmup under tile
heating. Although this warms the floor well and takes the cold edge out
of the room it isn't warm enough to keep the conservatory doors open
into the house so it isn't getting much use during the winter. I would
like to use a free standing heater on a timer so I can set it up to run
at the same time as the central heating so the room is still part of
the house (if you know what I mean). So I really would like to know
which type of heater would be the cheapest to run. I have been leaning
toward oil filled but I may be wrong am I ?


--
Alec

With electric heater the energy output is exactly the same as the
energy input.

If you feed, say, 3kW in as electricity you will get exactly 3kW out in
some form of energy. Unlike oil, gas etc. there is no "wasted fuel"
going up a flue.

So, the only question is what sort of energy comes out?

Those I can think of a

1) Heat - this is good as it's what you want (and it's generally what
electricity is happiest turning into) you can assume that anything you
can't otherwise account for ends up in heat.

2) Light - Most electric heaters give out a little light, if only in
the "on" indicator. The indicator uses so little that you can ignore
that. Most give out very little light for the element (have you ever
tried to see by the light from a 2 or 3-bar fire?). Halogen heaters
give off a reasonable amount, but this probably accounts for well under
5W. Also that light doesn't stay as light, when it is absorbed by
surfaces in the room it gets converted to heat, so the only light that
is actually wasted by a heater is the amount thag escapes through
windows (quite a lot in a conservatory!)

3) Sound - a very tiny amount of energy is converted into sound, and
this can really be ignored.

4) Movement - This could be in the form of some sort of rotation of the
heater head (I've seen this on some halogen units) or movement of air
by a fan heater. But again, this energy doesn't just "vanish", it gets
converted into heat eventually (basically friction losses).

So, 3kW electricity in gives as close to 3kW heat out that there is no
point comparing.

You forgot te EM field radiated by the elements. Get your tinfoil hat on
now!

Probably at least as powerful as living 500 meters from an overhead power
line :-) :-)