Just how much power can a fan oven consume...?

[Terry Fields]

The problem with pre-heat or not depends on the thermal properties of the food.

Once upon a time I used to carry out physical tests at elevated temperatures on special materials. The oven supplier for the testing machine provided a handbook, which suggested one of three heating heating regimes depending on the thermal properties of the material being tested. Regrettably I can't now recall what the properties were, but the results fell into one of three categories that played the greatest part in heating the specimens (partly dependent on their dimensions): convection, radiation, or a combination of both. The idea was to ensure that the specimens equilibrated at the elevated temperature in the shortest time, due to degredation.

Cooking a pie is rather similar, the radiative effect might play a significant part on the food-heating process. However, radiant heat is dependent on the fourth power of the temperature, so essentially the maximum benefit will be gained when the oven has reached the cooking temperature recommended for that product, with not much contribution up to that point. So putting a pie in a cold oven and turning on, might result in much less radiative flux reaching the food, and so the product could be undercooked.

For an oven that reaches temperature in a very few minutes this might not matter much for a product that takes say 10 times that interval to cook properly, but 15 minutes in an oven that takes 5 minutes to heat could make a significant difference.

[Terry Fields]

Mine flashes at the rate of 3200 per kWh, so one per second would be equivalent to 9/8 kW, a very useful factor (not) to use when standing in the cold trying to estimate the power draw. When I was given a monitor, it made things so much easier....

[Andy Burns]

397 units last month.

[polygonum]

on special materials. The oven

three heating heating regimes

I can't now recall what the

the greatest part in heating the

combination of both. The idea was

shortest time, due to degredation.

part on the food-heating process.

essentially the maximum benefit

for that product, with not

turning on, might result in much less

matter much for a product that takes

takes 5 minutes to heat could make a

Makes sense. But putting a pie with a cold centre into an oven with high radiant heat (i.e. full pre-heated) can cause the pastry to brown and even burn before it has fully heated through. Hence, in my book, bung it in a cold oven, and take it out when centre is hot PLUS aesthetically browned to desirable point. Even if that takes longer than the packet says. But that does need a thermometer or other means of checking pie interior temperature. I believe that in many cases that might reduce overall fuel consumption. Probably not all cases and possibly by a very slim margin.

It also matters what the pie is placed on in the oven.

[Dave Plowman (News)]

How much radiant heat in a fan assisted oven at about 190C?

[Terry Fields]

Quite a lot, that's why roasts like potatoes are put on the top shelf, it's nearer a radiating surface.

[DerbyBorn]

Terry Fields wrote in news: [e-mail]:

Fan ovens that I have seen have the element at the back wrapped around the fan. The fan disperses the heat in all directions.

[Terry Fields]

The radiated heat comes from the hot black surfaces of the interior of the oven; for stuff on the top shelf that means essentially the roof of the oven.

It's one reason why it isn't recommended to line the oven with ally foil, which gives a much lower amount of radiated heat - the ally has a very low emissivity.

[Dave Liquorice]

About 2000 in the last 28 days. Bloody E7 and storeage heaters...

[<me9]

How are you measuring it? if a current probe on the incoming tails it will be measuring KVA. I find that our microwave (inverter type) mains filter consumes when not in use enough(capacitive)KVA to mask most of the load imposed by the fridge or freezer, which have a large inductive loading.

[Chris J Dixon]

But did her oven have a fan?

Chris

[Peter Parry]

The "hotter at the top" came from gas cooker days and specifically the advertising of the Radiation cooker company in the 1920's when they introduced the New World cooker with Regulo control and gas burner at the back, rather than underneath.. Initially only controlling gas flow (and overcoming the problem of early gas supplies where pressure varied as more people turned on cookers for dinner) the Regulo later became a thermostatic control.

The company promoted the predictable temperature gradient of about

40deg C caused by having a fire at the bottom and a vent for the combustion products at the top as a positive advantage and enabling you to cook a whole dinner at once and without constant attention,

They advertised their cookers as having different "zones of heat". You had a span of about 3 "Regulo numbers" between the bottom and top of a Regulo oven so could cook a whole dinner of fish, meat, vegetables, sauce and pudding at once and for the same time, the roast at the top, the vegetables in the middle and the rice pudding at the bottom. You put your dinner in the oven and relaxed with your glass of sherry (medicinal purposes only) until dinner time arrived and everything was served.

Each oven came with a proper cookery book which included some really exotic dishes such as curry.

[Gordon Henderson]

Ah yes! My grandparents (who I lived with when younger) had one of those cookers. There was a pilot light in the middle and a separate gas torch that you used to light the oven (light the torch off the pilot, then transfer it to the pilot hole at the front of the floor of the oven.

Current oven is a Stanley range cooker - and it's definately got its hot spots and cooler areas - top left is hottest, so cakes baked in the middle do need turning half way through. It's no big deal - annoying at times though.

Gordon

[Dave Liquorice]

Curent transformer around the tails to a "CurrentCost" monitoring unit.

My AC theory isn't up to this lead/lag, inductive v capacitive loads stuff. My simple brain says that there is a change when an inductive load (fridge or freezer) comes on so this ought to be visible.

[Andy Champ]

nearer a radiating surface.

Interesting. You make it further from the surface, but at a better angle to it, and also expose it to more radiation from the side walls. Are you sure it makes any difference? (I'm certain it wouldn't in a spherical oven!)

Andy

[Terry Fields]

An interesting test would be to peel and par-boil a spherical potato, then pop it on a baking tray so that the top of it (the potato) is 1" from the top of the (fan) oven, but centrally located, say

6" from each side and the back (i.e. top shelf in the centre) of the hot oven. Observe which parts of it brown first, and how fast.

When the top of the potato has cooked to your satisfaction, remove, dip in butter, and eat...

[Andy Champ]

it on a baking tray so that the top of

say 6" from each side and the back (i.e.

first, and how fast.

You need to repeat this with identical potatoes in different parts of the oven. You'll obviously need to run each location several times to help remove any effects from the oven warming up over time, and also you must have three people running the experiment - one to place and cook the spuds, and another one to serve and record the experimentee's results.

Actually thinking about it this would make a good project for a school.

butter, and eat...

Did anyone say diet?

Andy

[Thumper]

If its a conventional oven it would need pre-heating up to temperature, then cook for 20 minutes. A fan oven doesn't need to pre-heat, so the pie can go straight from fridge to oven to cooked in 20 minutes.

Or you could microwave it in about 3.

[Dave Plowman (News)]

IMHO, bollocks. Neither of my fan ovens gets up to heat quickly. The smaller one takes about 8 minutes to 200C. Food heating details usually gives a lower temp for fan ovens - not a shorter time. Probably a different thing with much longer cooking times, though.

[Thumper]

Yeah for 200C in a conventional it would be around 180C in a fan oven. Although I don't need to pre-heat before putting food in, I do add about 5 minutes to the cooking time at the end, just to make sure.