How much does it cost to leave a professional oven switched on without using it?
A professional combi oven can have a connected load of 9, 18 or perhaps 30 kW. It may sound expensive to leave it switched on for several hours, but the connected load does not actually tell you much about how much electricity the oven uses.
There is a big difference between heating up a cold oven, preparing food and simply keeping the oven warm between production runs.
So how much does it actually cost to leave the oven switched on without using it? And when is it worth switching it off?
A 9.4 kW oven does not use 9.4 kWh per hour
Let's take a specific oven as an example: UNOX CHEFTOP MIND.Maps PLUS XEVC-0511-EPRM.
It is an electric combi oven with room for 5 GN 1/1 trays and a connected load of 9.4 kW.
If the oven drew 9.4 kW constantly, it would use 9.4 kWh in an hour. At an electricity price of 1.50 kr. per kWh, that would cost 14.10 kr.
But that is not how the oven works in practice.
When you turn on a cold oven, the heating elements work intensively to reach the desired temperature. Once the temperature has been reached, the oven primarily needs to replace the heat that escapes through the cabinet, glass and ventilation.
The heating elements therefore do not need to be active all the time.
This means that the oven's average electricity consumption can be significantly lower than the connected load.
How much electricity does a combi oven use on standby?
This depends on several factors, including the oven's size, insulation, temperature and operating mode.
The American ENERGY STAR program tests professional ovens and records, among other things, their Idle Energy Rate. This is the average energy consumption when the oven maintains a stable temperature without food in the oven chamber.
One example is an UNOX CHEFTOP-X combi oven with room for 6 GN 1/1 trays. It has a measured standby consumption of approximately 0.80 kWh per hour in hot air mode.
At an electricity price of 1.50 kr. per kWh, this amounts to just 1.20 kr. per hour.
This is significantly less than you might expect from a professional oven with a connected load of 12.5 kW.
And this shows why it is misleading to calculate electricity consumption based on the oven's connected load alone.
How much does it cost to keep a CHEFTOP-X warm?
Based on the measured standby consumption of 0.80 kWh per hour, we can calculate how much it costs to leave the oven warm without using it.
| Standby time | Electricity consumption | Cost |
|---|---|---|
| 30 minutes | 0.40 kWh | 0.60 kr. |
| 1 hour | 0.80 kWh | 1.20 kr. |
| 3 hours | 2.40 kWh | 3.60 kr. |
| 8 hours | 6.40 kWh | 9.60 kr. |
If the oven is left warm without being used for three hours a day, 250 days a year, this amounts to a total electricity cost of 900 kr. per year.
That is money, of course, but perhaps less than you had expected.
The calculation is based on ENERGY STAR's measurement of the oven in question under standardised test conditions. Electricity consumption will differ at other temperatures and operating modes.
We have used an example price of 1.50 kr. per kWh excluding VAT. If you want to calculate the cost for your own restaurant, you will need to use your actual total electricity price.
How much does a UNOX CHEFTOP PLUS use on a working day?
Standby consumption only tells part of the story. In your kitchen, the oven is of course also used to prepare food, and this requires more energy than simply maintaining the temperature.
Here we can take another oven as an example: UNOX CHEFTOP MIND.Maps PLUS XEVC-0511-EPRM, which has room for 5 GN 1/1 trays.
UNOX states an estimated energy consumption of 21.7 kWh per working day for this model.
The calculation is based on the following production:
- Six smaller portions of chicken, with the oven filled to approximately 20%.
- One full oven of potatoes.
- Three full ovens with steam cooking.
- Two hours of standby at 180 °C.
- An estimated contribution from cleaning programmes.
At an electricity price of 1.50 kr. per kWh, this amounts to approximately 32.55 kr. in electricity on a working day.
This is, of course, not a precise calculation of what the oven will cost in your restaurant. It depends on how much you prepare, which programmes you use and how long the oven is switched on.
But it gives a more accurate picture of electricity consumption than simply multiplying the oven's connected load by the number of operating hours.
It is also worth noting that the 21.7 kWh includes active cooking, standby and cleaning. UNOX does not state what portion is due to standby alone.
You can try this online calculator yourself based on the requirements of your kitchen: UNOX's energy calculator
Is it worth switching the oven off between cooking runs?
If the oven is to remain unused for a longer period, it is worth considering switching it off. But during a busy service, this is not necessarily the best solution.
When you switch the oven off, it begins to lose heat. The longer it remains switched off, the more energy it will need to reach the desired temperature again.
If you switch the oven off for 15 minutes, the oven chamber will still be warm, and reheating will normally be limited.
If, on the other hand, it remains switched off for several hours, more energy will be needed to heat it up again.
Therefore, there is no single time limit that applies to all ovens.
And there is also another consideration: waiting time.
If your chef needs to use the oven again in 20 minutes, it may be impractical to switch it off, even if you might save a little electricity.
Conversely, there is rarely a reason to keep the oven at 180 °C all afternoon if the next cooking run is not until the evening.
Planning can be more important than electricity consumption
Imagine you run a restaurant where the combi oven is used for preparation in the morning and again during the evening service.
If the oven is left warm from 12:00 to 17:00 without being used, you can probably reduce electricity consumption by changing the routine.
But you may be able to save even more by looking at how production is organised.
Can you combine several cooking runs at the same temperature? Can you prepare some dishes earlier? And does the oven need to be ready at full temperature while staff are carrying out other tasks?
In practice, these are often the most interesting questions.
It is not just about using fewer kilowatt-hours, but about making production work efficiently without unnecessary energy consumption.
Five practical tips for reducing the oven's electricity consumption
1. Do not switch the oven on earlier than necessary
If you do not need to use the oven until 11:00, there is no reason to switch it on at 8:00. Find out how long your oven actually takes to reach the desired temperature.
2. Combine cooking runs at the same temperature
If you need to prepare several different ingredients at 180 °C, for example, it may be an advantage to plan them one after another rather than leaving the oven warm between production runs.
3. Use the oven's automatic functions
Modern combi ovens often have functions that make it easier to control cooking and plan work. Also find out what energy-saving operating and automatic start options your specific oven has.
4. Avoid opening the oven door unnecessarily
Every time you open the door, hot air escapes. The oven then needs to use energy to restore the temperature.
This does not mean that you should refrain from checking the food, but frequent and unnecessary openings increase energy consumption.
5. Choose an oven that suits your production
A large oven may be necessary during peak periods, but if you often prepare small portions, it may be worth investigating whether a smaller oven or a different distribution of capacity is better suited to your kitchen.
Should you switch the oven off or leave it warm?
Our recommendation at Cosina is to distinguish between short breaks during production and longer periods when the oven is not needed.
If you use the oven continuously during a busy service, there is rarely a reason to let electricity consumption alone determine whether it should be switched off.
But if you know that the oven will not be needed for the next three or four hours, it makes good sense to switch it off or use a relevant energy-saving function.
You do not necessarily need to buy a new oven to reduce your electricity consumption either. Often, you can make progress by changing a few routines in the kitchen.
The most important thing is not to keep the oven switched off as much as possible. It is to avoid unnecessary energy consumption without making the work in your kitchen more difficult.
