On 2007-12-25 09:45:29 +0000, said:

According to Wikipedia, coal is about 6.67 kWh/kg. According to Aga
you need 47.5kg of fuel a week. My only issue with agas is that when
you want to cook, but don't want the heat all day, that's when you
start to waste money.

No you don't. The whole point of the massive heat store is that the
average over the day is very small and there is plenty in reserve for
cooking. The few hundred watts of released heat contributes to the
space heating as well as being a very effective way of drying
slobberadors, Maine coons and chilis from the greenhouse.


Yes you do.

No you don't

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.

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


The vast majority of that energy is not
used for cooking.

It doesn't matter. It contributes towards space heating.


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.



If someone had a
normal electric cooker, but left a 1kW electric heater on all the time
in their kitchen in case a wet dog walked past, you might be forgiven
for thinking they were a bit daft!

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.




But for gas it's even worse!

No it isn't.


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.

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. The latter *could* consist of heat released
through the case and that would be true if the appliance were installed
in an outbuilding as opposed to in the kitchen, where a small amount of
space heating is wanted.

The other component would be energy released through the flue. Aga
have three options. A conventional flue, a convection balanced flue
and a powered flue using small diameter pipe and a fan.
The latter two of these of course would result in quite a bit of energy
loss through the flue, much as it does with a conventional boiler
having a similar arrangement.

I have a conventional flue which runs inside the house through two
storeys before passing through the loft and eventually exiting on a
ridge tile vent. By the time it is entering the roof space, it is
barely warm, most of the heat having been given up in the envelope of
the house.




The problem with rapid heatup is that there is rapid cooldown as well
and it becomes very difficult to regulate temperature.

I hope to find a cooker that will heat up in an hour or so. That way
in milder weather I'll let the fire go out when I don't need it. I
imagine I could light it when I got in from work, and when I'm ready
to cook, it will be too. It's up to me whether I keep the fire going
till morning or all day.

Sounds like a lot of trouble.....



What do you recommend for a second cooker by the way?

Nothing. It isn't necessary.