My oven probably takes about 10 minutes or so to get to 400 F. Why? The volume is probably no more than 15 cubic feet. Why wouldn’t there be a way to get it to 400 almost immediately? Is this limitation due to technology and/or cost?
The mass of the oven itself has to come up to temp.
Because it takes a while for the metal parts to come to 400°? I expect the cost to heat those parts instantly would be a tad high, plus it would add to the complexity of the appliance.
The limit mainly comes from the standard electrical service for your home.
In the U.S., you typically have a 240 volt outlet (assuming that your kitchen is set up for an electric stove and not gas) which will be rated somewhere between 30 and 50 amps. Your stove has to be sized so that it won’t blow the breaker even if you have all four burners on plus both oven heating elements. If you put in more powerful heating elements so that your oven would heat up faster, you would blow your breaker.
More powerful commercial ovens exist, but they run on 3 phase power and not the single split phase power that you find in a typical house. You would have to get a fairly major upgrade to your home’s electrical service to provide that kind of power.
Speaking of 3 phase power, some residential service comes from 2 legs of a 3 phase system instead of the single split phase service that most homes have. In this case, instead of 120/240 volt service, you end up with 120/208 volt service. This is common in large apartment buildings, commercial buildings (applicable if you have an oven in your break room or whatever), and in rare cases can be found in some single family homes in dense areas of cities. Since you have 208 volts instead of 240, it will take longer for your oven to preheat. It will also take longer for your clothes to dry if you have an electric dryer.
The rest of the limits comes from basic thermodynamics. You have heating elements sized for the maximum amount of power you can draw from the outlet, heating a certain amount of air and metal.
Gas ovens heat a bit faster than electric, but they are limited by how much gas you can get from your supply line.
You’re waiting for the air inside the oven to reach the desired temperature, and air is a very poor conductor of heat.
Air isn’t a good conductor but the air in an oven is heated radiantly and by convection not conductance.
The real problem is the mass of the oven itself. Until the walls heat up they are absorbing the heat from the air, and keeping it cool.
If it were only the air that needed to be heated, it could be heated in seconds.
An interesting data point here is that the oven in my old electric stove in a previous house heated up so fast that people would comment on it. It was a self-cleaning oven so I just attributed it to the fact that it was well insulated. Yet the current stove, which also has a self-cleaning oven of about the same size, takes a lot longer even though it has a larger bake element with a higher wattage rating.
I’m wondering now whether it was possible that the old stove turned on both bake and broiler elements when preheating, though I can’t really remember noticing that. One thing for sure is that the old stove had a fully exposed bake element, while in the current one it’s covered by a heavy metal plate. That helps to provide more even heat but would understandably take longer to heat up.
Makes sense.
Insulation matters a lot, too. When we replaced our stove, one of the first things I noticed is that the oven heated up a lot faster. Also, the kitchen didn’t get nearly as warm while the oven is in use. It’s a gas oven, so it still needs to vent hot air (and get fresh air for the gas to burn) but the difference is huge.
The jump from room temperature to 400 degrees is a very big one. I don’t consider ten minutes to be an inordinate amount of time. It takes about 15 minutes or more to boil (212 degrees) a 16 inch diameter pot of water for pasta.
Just the other day on Startalk Neil DeGrasse Tyson mentioned calculating how long it would take to bake a pizza on a windowsill on Venus. He came up with seven seconds but somebody pointed out he’d considered only convection, not radiant heating. Factoring that in lowered it to three.
My mother is in a high rise condo with 208/120V service. The stupid oven takes FOREVER to preheat.
It could “know” that none of the burners are on, and allow the oven to draw more power. Some multi-car chargers - such as for apartment buildings - are starting to work this way. Of course, this would add complexity and cost.
I have a modern electric fan oven (Miele) that is very well insulated. The power supply is 230V and 30 amps but it still takes ten minutes to get up to 200C
This, at least the part of the oven contained inside the insulation.
I did the math for my own ordinary-sized oven (interior = 2’ wide, 1.5’ deep, 1.5’ tall), assuming steel thickness of 0.75 inches and a power of 6900 watts. The air in the oven weighs about 2 pounds, but the steel inner shell weighs about 50 pounds, and that’s where very nearly all of the heat energy goes. To get from room temperature to our target temp (68F to 400F, 20C to 200C), you have to give the air 28 kJ of energy, and you have to give the steel 8541 kJ of energy. Grand total, 8569 kJ. for a heating element power of 6.9 kilowatts, that takes 20.6 minutes. Note that this analysis ignored the ongoing thermal losses through the insulation, which will slow down the temperature increase rate in the later stages of preheat. It also ignored the mass of the racks, but compared to the 50-pound steel shell, I think the racks don’t contribute much mass.
Want a faster preheat? You’ll either need a more powerful element (and better house wiring), or you’ll want an oven made out of less steel. That means a smaller cook chamber, or thinner sheet metal. The mass of the steel walls is virtually the entire problem. Take my example above: if you cut the thickness of the steel from 0.075 inches down to 0.0375 inches, the preheat time goes from 20.7 minutes down to 10.38 minutes. And nobody wants an oven with 0.0375-inch walls; they’ll dent if you drop a spoon against them.
Would the thinner steel also mean that the temperature would vary more and the oven has to cycle on/off more often? From you you wrote, it seems like the thicker steel would retain heat better and mean the oven would stay at the selected temperature longer.
After preheat is done, the range between min/max temperatures is mostly related to how tightly the thermostat controls things; you could have a thermostat that turn on at 395 and off at 405, or one that turns on at 375 and off at 425.
Assuming a fixed heating power and insulation thickness, the speed with which the oven temp varies will be affected by the total thermal mass, and that’s where the steel thickness matters. I suspect the food being cooked is affected more by the min/max temperature range than it is by how frequently the oven temp varies between those two extremes.
You could bond it to a rigid, insulating backing, though. You probably don’t want bare ceramic walls, since they’d absorb moisture and volatiles, not to mention being too brittle, but a thin metallic layer should be sufficient protection.
Some plastics might be reasonable as well. PEEK plastic for instance would be fine up to 250 C.
It takes way more energy to heat water than to heat air.
Go read Machine_Elf’s post. Or indeed about 3/4 of the posts above yours. It ain’t about the air.