# What is a good way/formula to approximate heat/energy loss of not fully sealed electric oven filled with only air?

I made an electric furnace that consume ~18 kW (3 phase) of power. I want to know how much energy is lost when its used to heat only air. The only sensing tool available as of now are thermocouple installed inside and amperemeter. It took approximately 250s to reach 500°C from 25°C. It's not fully sealed so there are some holes for air to go in and out.

Cant seem to make up my mind to decide which factor I should consider for the heat loss.

To add, it's an electric furnace and has temperature limit set to certain degree (500°C in my case, can be changed). At that point the contactor will start turn on and off to keep temperature constant. All I know is that it consume constant 27.3 A when its powered. That's where I got 18 kW from.

• Wait for thermal equilibrium then measure the energy input. Commented Jun 18, 2022 at 19:12
• Can you elaborate on thermal equilibrium? Since its and electric furnace and has temperature limit set to certain degree (500°C in my case). At that point the contactor will start turn on and off to keep temperature constant. All I know is that it consume constant 27.3 A when its powered. Thats where I got 18 kW from. Leaving it powered with no limit could risk overheating and breaking component inside. Commented Jun 18, 2022 at 19:21
• Who said remove the limit? Commented Jun 18, 2022 at 20:22
• There are lots of equations to calculate heat loss. This is a good portion of a heat transfer course. Though most ovens don't have holes in them becaue usually you only want to heat the inside. Commented Jun 19, 2022 at 23:00