log burner
 

log burner
 

On Mon, 24 Dec 2007 07:29:23 -0800, tom.harrigan wrote:

According to Wikipedia, coal is about 6.67 kWh/kg. According to Aga
you need 47.5kg of fuel a week.

I thought agas burned smokeless coal, which will be nearer to coke and
hence less volatiles (hydrocarbons), so I was referring to the lack of
water in the flue gases, so you could run a very low flue gas
temperature, as long as the little water never saturated the flue gas.

My only issue with agas is that when
you want to cook, but don't want the heat all day,

Which is why a modern solution is a gas cooker and gas central heating
system. If I needed to heat with wood and cook with wood I doubt I'd try
to get one device to do the same job and there are some reasonable
solutions to cooking with wood, some 2 billion people depend on it.

AJH

log burner
 

andrew heggie wrote:
On Mon, 24 Dec 2007 07:09:30 -0800, tom.harrigan wrote:

aga suggest you need 47.5kg of
solid fuel to get 220kWh. Unless I've done something wrong, that makes
it about 70% efficient.

I haven't checked your maths, nor do I know the calorific value of your
fuel but coke burning devices always look good because the LHV
and HHV are the same. My beef with the aga is that it gives you the heat
when it wants to. Now this is fine with solid fuels because they all have
this thermal inertia problem but it's an unnecessary restriction when
burning inherently "better" fuels like gas or oil.


The aga ticks over at around 1KW continuous. Thats about right we find
for march to June, and September to November. That heats about 200
square meters of house floorage.

June,July and august, its out.

December January and February we chew three times as much oil heating
the house conventionally with an oil boiler, as the aga uses all year.

Then the aga is capable of heating just the kitchen, about 30 sq meters.

The key to all this is plenty of thermal mass in the house. It makes
more sense with a high occupancy ratio.

which we have also. The house is seldom empty for more than 2 hours.

To be honest, if we had 24x7 wood burners all over he place, ticking
over at 1kw per room,. that would be fine as well..if you bother to
manage them.

I guess thermostatically controlled dampers might be useful as well.

Bur the great thing about burning fuel where you are - and free fuel at
that - is that its very efficient and low collateral energy fuel.

15 minutes with a chainsaw (about 100cc of petrol) and 20 minutes with a
hatchet has me a weeks supply of firewood. I'd estimate something like
300kwh worth. In terms of open fires. More if nrnt in a stove.


Probably around £15-£20 of oil equivalent. At least. More in a stove. A
lot more.

BUT it needs managing..







AJH

log burner
 

On 24 Dec, 15:42, The Natural Philosopher wrote:
wrote:
On 24 Dec, 09:13, The Natural Philosopher wrote:
andrew heggie wrote:
On Sun, 23 Dec 2007 18:42:00 +0000, The Natural Philosopher wrote:
Some types of woodburner, masonry stoves, actually use a massive fireplace
to absorb heat and then release it into the room slowly, these burn at a
very high power and wouldn't work with an insulated flue as they depend on
the flue passage as a heat exchanger, a bit like roman hypercausts.
Odd that. as the aga which is essentially that, was specified for an
insulated flue. Albeit of a lower spec than the wood burner.
The aga is massive but its flue is just a means of exhausting the gases,
there's no scope for getting more heat out of the flue gases so they
should not be cooled further, and as they are already quite cool they can
use a cheaper liner if fired on smokeless fuel, gas or oil. The aga I
mentioned earlier that would not draw simply did not have enough heat in
the flue gases to warm the massive chimney it was exhausting into, as well
as the other problems I mentioned.
The masonry fire is actually built into the chimney breast that then
becomes a "radiator" and thermal store, so the flue reaches high
combustion temperatures but is cooled by the massive structure. I'm not
familiar with them but I would expect the flue gases to actually leave the
top at a similar temperature to a conventional wood stove 150C.
No. You can put your hand on the stove pipe. It's nearer 60-70C. For an aga.

VERY efficient heater. More so than a condensing boiler IMO.

AJH

I was dubious about your claim that agas are efficient, so I did a
little calculation. Assuming that a solid fuel aga requires the same
amount of energy whatever the fuel, aga suggest you need 47.5kg of
solid fuel to get 220kWh. Unless I've done something wrong, that makes
it about 70% efficient. That's pretty impressive for a slow burning
cooker!

My guess is thats about right. Ours certainly is a heater first, cooker
second as far as I am concerned. Its oil tho. not solid.

You could get even more with flue heat recovery type stuff.

It ought to be possible to calculate efficiency from burner temps
(bright orange/yellow?) and flue temps..as I said about 55C at the top
of the stove pipe where it enters the flue..

T

For oil, the efficiency is worse according to Aga - about 54%
efficient. That's the price you pay for the silent operation!

T

log burner
 

On Dec 24, 3:29*pm, wrote:

According to Wikipedia, coal is about 6.67 kWh/kg.

A lot depends on what sort of coal it is.

Also according to Wikipedia anthracite has an LHV of 33MJ/kg which
gives 9.17kWh/kg.

I doubt Aga owners will be feeding their beast on 'value' brown coal,
more like /Finest/ smokeless or anthracite :)))

cheers,
Pete.

log burner
 

On 2007-12-24 15:09:30 +0000, said:

I was dubious about your claim that agas are efficient, so I did a
little calculation. Assuming that a solid fuel aga requires the same
amount of energy whatever the fuel, aga suggest you need 47.5kg of
solid fuel to get 220kWh. Unless I've done something wrong, that makes
it about 70% efficient. That's pretty impressive for a slow burning
cooker!

T

It cooks turkies very nicely as well :-)

log burner
 

On 2007-12-24 15:16:41 +0000, andrew heggie said:

On Mon, 24 Dec 2007 07:09:30 -0800, tom.harrigan wrote:

aga suggest you need 47.5kg of
solid fuel to get 220kWh. Unless I've done something wrong, that makes
it about 70% efficient.

I haven't checked your maths, nor do I know the calorific value of your
fuel but coke burning devices always look good because the LHV
and HHV are the same. My beef with the aga is that it gives you the heat
when it wants to.

Actually not true.

The heated metal mass in the core of the cooker is very well insulated
from the exterior. The heat is therefore not released in substantial
quantities at all.




Now this is fine with solid fuels because they all have
this thermal inertia problem but it's an unnecessary restriction when
burning inherently "better" fuels like gas or oil.


Not at all. With a gas supply, the burner used is a modulating type,
the output of which is a few hundred watts when the core is fully up to
temperature. The burner output increases when heat is extracted for
cooking and other purposes.

log burner
 

On 2007-12-24 15:29:23 +0000, said:

On 24 Dec, 15:16, andrew heggie wrote:
On Mon, 24 Dec 2007 07:09:30 -0800, tom.harrigan wrote:
aga suggest you need 47.5kg of
solid fuel to get 220kWh. Unless I've done something wrong, that makes
it about 70% efficient.

I haven't checked your maths, nor do I know the calorific value of your
fuel but coke burning devices always look good because the LHV
and HHV are the same. My beef with the aga is that it gives you the heat
when it wants to. Now this is fine with solid fuels because they all have
this thermal inertia problem but it's an unnecessary restriction when
burning inherently "better" fuels like gas or oil.

AJH

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.



If I could afford to run one, I'd probably get
one. At the moment I'm after a solid fuel cooker that's a bit more off-
and-on-able. It's quite difficult getting information on heat up
times, but I reckon the Stanley Errigal should heat up fairly quickly,
though I do prefer the look of the Rayburn 300W or Esse woodfired
cooker.

T

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

log burner
 

On 2007-12-24 15:55:36 +0000, The Natural Philosopher said:

The aga ticks over at around 1KW continuous. Thats about right we find
for march to June, and September to November. That heats about 200
square meters of house floorage.


Have you measured this by oil consumption?


I timed the gas meter with the cooker in the steady state and go a
figure of about 700W.

log burner
 

On 24 Dec, 21:22, Andy Hall wrote:
On 2007-12-24 15:29:23 +0000, said:



On 24 Dec, 15:16, andrew heggie wrote:
On Mon, 24 Dec 2007 07:09:30 -0800, tom.harrigan wrote:
aga suggest you need 47.5kg of
solid fuel to get 220kWh. Unless I've done something wrong, that makes
it about 70% efficient.

I haven't checked your maths, nor do I know the calorific value of your
fuel but coke burning devices always look good because the LHV
and HHV are the same. My beef with the aga is that it gives you the heat
when it wants to. Now this is fine with solid fuels because they all have
this thermal inertia problem but it's an unnecessary restriction when
burning inherently "better" fuels like gas or oil.

AJH

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. 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. The vast majority of that energy is not
used for cooking. Your aga will be giving off at least a kW of "waste"
power all the time it is on - which is all the time. 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!

But for gas it's even worse! 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.

If I could afford to run one, I'd probably get
one. At the moment I'm after a solid fuel cooker that's a bit more off-
and-on-able. It's quite difficult getting information on heat up
times, but I reckon the Stanley Errigal should heat up fairly quickly,
though I do prefer the look of the Rayburn 300W or Esse woodfired
cooker.


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.

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

T

log burner
 

On 24 Dec, 20:43, Pete C wrote:
On Dec 24, 3:29 pm, wrote:

According to Wikipedia, coal is about 6.67 kWh/kg.

A lot depends on what sort of coal it is.

Also according to Wikipedia anthracite has an LHV of 33MJ/kg which
gives 9.17kWh/kg.

I doubt Aga owners will be feeding their beast on 'value' brown coal,
more like /Finest/ smokeless or anthracite :)))

cheers,
Pete.

I suppose inferior fuels are unlikely to be used by aga owners. In
which case the solid fuel efficiency is on a par with gas and oil -
ie. really bad considering we are in the 21st century.

Some people care about environmental impact, and are prone to
measuring this in terms of CO2 produced. I reckon that an Aga, left on
all the time, will produce the following emissions:

solid fuel: 6.8 tonnes CO2
oil: 5.2 tonnes CO2
gas: 4.2 tonnes CO2

Isn't the average CO2 per person in the UK about 10 tonnes!

T

log burner
 

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.

log burner
 

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.

- 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!

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.



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!



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).

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.

log burner
 

On 2007-12-25 13:10:47 +0000, said:

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 did. 700W is "a few hundred". It's not a "few thousand" is it?
I have always consistently said that I have measured an inout rate of
700W in the steady state.


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.

Please yourself. I know what I measured and Aga's figures for gas
consumption are pessimistic.



If you were being honest with
yourself you would quote your gas consumption for the average week,
but you are not.

The only way to do that would be to have a separate meter just for the
Aga, since the main CH boiler is also gas. Taking a whole house
measurement would be pointless anyway because gas consumption depends
on the size of the house, the insulation and the pattern of hot water
use. It is reasonable to take the Aga consumption is isolation with
the boiler turned off because the heat input is practically constant
and very much less than the requirement for the house in total.



Strangely, my central heating consumption is pretty
low too when my house is up to temperature.

Likewise.



- 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.

During the heating season, if the heater were gas and contributing
virtually all of its heat into the house, it would be entirely
reasonable.


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!

I measured approximately 30% of that based on the gas input rate.



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.

You're getting confused.


Please don't be so foolish as to argue this point, just
give it a moments thought instead.

I have.


If you claim that an aga can be
kept at temperature by 4 lightbulbs, I will just laugh.

I haven't said that, and neither have I mentioned any efficiency
figures, let alone 52%. The gas input rate, measured, is 700W in
steady state.

You are arguing from sets of figures that you have pulled from goodness
knows where.


I thought it
was "a few hundred watts" anyway.

700W is a few hundred watts.





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 if you read what I wrote rather than what you think I wrote.
This was one of the reasons for disposing of a "conventional" cooker
and hob.






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.

On the contrary, you are.

Do you own an Aga? No.

Have you actually measured one? No.


An aga needs 220kWh
of heat a week according to aga. A gas aga requires 425kWh of gas a
week according to aga.

I already told you that the figures are conservative. They also
don't specify the pattern of use.



The inefficiency has nothing to do with heat
being released where it's not wanted.

Of course it does.


It seems agas are just over 50%
efficient whatever the fuel (apart from electricity).

That would depend on how you measure efficiency.



The other component would be energy released through the flue.


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

That depends on what is measured and where. If you measure in terms
of energy in and what comes out of the flue immediately at the
appliance, it is one thing. However, if the flue runs through the
envelope of the house and gives up further heat there, where it is
wanted, then that certainly contributes towards overall system
efficiency.

I am certainly not going to fuss over the difference of a few hundred
watts of heat in the cooker, when the boiler is using at least an order
of magnitiude more heating the rest of the house and the hot water.
It is also why I won't have anything to do with low energy light bulbs
and all the other silly green nonsense.




Here's a recent article you might find enlightening:

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

Not really. The Independent is only marginally less of a rag than the
Guardian. Nothing written therein can be relied upon as trustworthy.

I am not in the least bit interested in articles by people who choose
to pontificate about the carbon emissions that others make.

As soon as the guy starts to make comments like "society urgently moves
to a carbon-negative economy" and makes comparisons with solar electric
panel installations then it is safe to say that he is testiculating
(i.e. waving arms around while talking ********).






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.

If I had bothered to implement an additional cooker, it would hardly be
used and would frankly gather dust and use space. Even the microwave
is seldom used.

log burner
 

Pete C wrote:
On Dec 24, 3:29�pm, wrote:

According to Wikipedia, coal is about 6.67 kWh/kg.

A lot depends on what sort of coal it is.

Also according to Wikipedia anthracite has an LHV of 33MJ/kg which
gives 9.17kWh/kg.

I doubt Aga owners will be feeding their beast on 'value' brown coal,
more like /Finest/ smokeless or anthracite :)))


Welsh dry steam coal mostly, It burns a little easier than anthracite.
Or coke or pre-made coaldust pellets.

Low bitumen content was the key. And low residual rock content to avoid
too much slag.

I'd hate to go back to coal fired anything frankly. Open fires maybe.


cheers,
Pete.

log burner
 

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.

log burner
 

Andy Hall wrote:
On 2007-12-24 15:55:36 +0000, The Natural Philosopher said:

The aga ticks over at around 1KW continuous. Thats about right we find
for march to June, and September to November. That heats about 200
square meters of house floorage.


Have you measured this by oil consumption?



Not really. I know its the least of my problems. Its a guesstimate.

My biggest problem is heatloss when the wind blows. A suspended concrete
floor with massive ventilation under it, plus two open chimneys and 6
underfloor ducts to feed them and the aga, plus uncertain hermetic
sealing on the walls..never mnond doors with keyholes in them.. Huge
draught through a keyhole..





I timed the gas meter with the cooker in the steady state and go a
figure of about 700W.



I wouldn't be surprised if we were at that. ISTR that the model in
question was supposed to be 600W of HEAT given off. I assumed that was
optimistic.

Heck we use that just running enough lights to light the corridoors and
main rooms at night.

log burner