Distinguish preheating from waiting
Record when the oven is switched on, when it signals readiness and when food goes in. The gap after readiness is a separate heated waiting period. That distinction reveals whether better meal preparation could remove idle heating while still following the recipe’s preheat requirement.
Use the same target temperature and a cold oven when comparing initial heat-up tests. A second meal cooked immediately after the first starts with stored heat and should not be described as a fresh cold-start measurement.
Calculate energy from average input
With an assumed average input of 2,400 W over 15 minutes, energy is 2.4 × 15 ÷ 60 = 0.60 kWh. At an illustrative $0.18/kWh, the cost is $0.108. Twenty such preheats would account for $2.16.
A separate ten-minute wait at a hypothetical 900 W average adds 0.15 kWh, or 2.7 cents. Removing that wait avoids this second amount, not all preheating energy. Neither average is a claimed specification for your oven.
Measure only with an appropriate method
A fixed or high-voltage oven is not a job for an ordinary plug-in energy meter. Use suitable appliance data or an already installed, correctly configured energy-monitoring system. Whole-home interval data can show a change, but simultaneous appliances make it difficult to attribute the entire increase to the oven. Mark that uncertainty rather than turning a rough graph into a precise appliance test.
Plan a useful change
Prepare ingredients and trays before starting the preheat so the oven is ready near the time you need it. Do not omit a required preheat or alter safe cooking instructions just to improve an energy number. When deciding between two appliances, compare the finished meal including all preheat and cooking stages. A device with a short warm-up can still use more total energy if it needs several batches.
Choose your next step
Continue with the question that matches your next decision:
Sources & further reading
Numerical examples are illustrative unless explicitly described as measured. This guide does not claim hands-on product testing. Read the methodology and editorial disclosure.