wrote:
On 25 Dec, 10:33, Andy Hall wrote:
On 2007-12-25 09:45:29 +0000, said:

If you care about needlessly throwing heat out the window,
then the 220kWh (270kWh for the 4 oven) it takes to run an aga a week
may be of some concern to you.
Two points.

- The figures provided by Aga are conservatively pessimistic. I have
measured my gas consumption at the equivalent of around 700W in the
fully charged steady state. It does, of course, use more when cooking
on the top plates.


So, a "few hundred watts" is now 700W! Please make up your mind. I
choose to accept aga's official figures which I consider overly
optimistic, based on the electricity bills of two neighbours who had
electric agas installed this year. If you were being honest with
yourself you would quote your gas consumption for the average week,
but you are not. Strangely, my central heating consumption is pretty
low too when my house is up to temperature.


The figure for around 700-1Kw is pretty much what I have found,
depending on the weather. At high room temps or when not cooking,its lower.


- Heat is not thrown out of the window any more than with any other
form of heating.


I'd agree if it were normal behaviour to leave a kW heater on
permanently, but it's not, and would be regarded as utterly foolish.
If the 425kWh of gas that a 2 oven aga uses a week were put through a
modern condensing boiler, that would be equivalent to 2.5kW heater!


But it is, you have a 10KW plus boiler constantly on and off,
maintaining temperatures throughout MUCH of the year.

As I said, in summer the aga is switched off. In winter its
supplemented. It is like 'baseband' heating then..its always there
operating at high efficiency. The lower efficiency non condensing oil
boiler is used for demand peaks. Or open fires,. but lets not muddy the
waters..


Now, I know, because ny stats and thermometers tell me, that this
particular house in winter, loses about 0.5C per hour when its around
19C inside and -2C outside.

By timing my heating I can - say - reduce the average temperature and
hence heatloss by a bit - but not by much. Sadly even if we went out to
work, the time the house is coldest is around 6 a.m. which is when we
are in it and need a bit of heat, in the bedrooms at least.


Its a very moot point as to whether the firing cycle of the boiler, or
having it ruin flat out at 10KW plus, with a lot of heat going up its
balanced flue which comes STRAIGHT from outside, is not infact hugely
less efficient than the aga, which has a 10meter conventional flue, and
draws its air under the floors where it gets a bit of warming first.

The more mass is in the house, and the more efficient the insulation,
the less it matters whether you time or not. I have to say that it
scarcely makes any difference here, in the ground floors with the huge
mass of screed above the insulation.

I do find that the upper floors of lightweight timber construction show
far bigger heatloss at night: To the point where we need to use heating
there in the wee small hours, and late at night too.


HOWEVBER iun SUMNMER we need to run fans up stairs - the solar gains are
such that its insuufferbay HOT especially where the computers are...
Whereass downstairs its cool..the mass helps reduce heat GAIN in summer,
and reduces any need to cool the place. So it actually works BETTER and
uses LESS energy in summer. Don't underestimate the cooling effect of a
large lump of cold aga, either.


Your aga will be giving off at least a kW of "waste"
power all the time it is on - which is all the time.
Incorrect. As I have said, I have measured mine in steady state at
around 700W and the heat is not wasted.


Incorrect. Your aga is cooling if it is only consuming 700W at 52%
efficiency. Please don't be so foolish as to argue this point, just
give it a moments thought instead. If you claim that an aga can be
kept at temperature by 4 lightbulbs, I will just laugh. I thought it
was "a few hundred watts" anyway.


Well essentially it can.

`The things are massively insulated. YOU put 4 lightbulbs inside a box
surrounded with rockwool and vermiculite and see how hot it gets
inside..Our aga runs at a case temperature of around 45-50C estimated,
and at a room temp of around 20-23C its seems to be losing around 700W
or so to the room.

Which is prefect for that room on its own in winter, or half the house
in spring and autumn. We simply leave the doors open,.


If someone has a "normal" electric cooker I think that they are a bit
daft. These things are poorly insulated to the point that the room
temperature can rise by several degrees. Hardly surprising when 10kW
is added to the room heating. Then the window has to be opened to
dump the wasted heat.



This is so funny, hoist by your own petard!

Not at all.

An aga doesn't DO 10Kw, unless yoou leave the oven doors open, when it
might for about ten minutes till it cools down and becomes unuseable as
a cooker..;




According to Aga, a 2 oven uses 425kWh of
natural gas a week, to produce 220kWh of heat. I suppose you could
take the view that you are wasting so much energy anyway, what's the
point in wasting a bit less by fitting a more efficient burner. A 52%
efficient burner is pretty shocking considering you can get range
cookers every bit as good as an aga with condensing burners nowadays.
Aga don't make cookers with condensing burners.


Sandyford do, so do Rayburn.

Leaving that aside, you are not reading and understanding the figures
correctly.

The energy efficiency depends on the gas used and the heat released
where it is not wanted.

You are the one with the comprehension problems. An aga needs 220kWh
of heat a week according to aga. A gas aga requires 425kWh of gas a
week according to aga. The inefficiency has nothing to do with heat
being released where it's not wanted. It seems agas are just over 50%
efficient whatever the fuel (apart from electricity).


Dunno. Try the oil one with a conventional flue. I'd say 75%.

Better than my oil boiler for sure.

The other component would be energy released through the flue.


You are conveniently ignoring the fact that the burner is of low
efficiency.

Here's a recent article you might find enlightening:

http://money.independent.co.uk/prope...cle3133377.ece



What do you recommend for a second cooker by the way?
Nothing. It isn't necessary.

I didn't say it was necessary - it's just sensible.

I use two electrics and a microwave as auxiliaries, but in summer it
tends to be a barbecue outside.


If the weather goes cold, we light the aga again..;-)

Only takes about 6 hours to come up to temperature.