Heat transfer question about heat tape in box

[blundin123]

I am trying to install heat tape in a box that will heat an object inside. I'm trying to design it so it goes from -40 to 20 degrees C.

I figures out that it will loss 900 watts of heat.

so, with heat tape being 9 watts/foot, does that mean I will need 100 feet of this heat tape or is this too simple?

 

[BridgeSmith]

If you're losing 900 Watts continuously through the box to the environment, you'd need more than 100 ft of heat tape to affect a temperature change inside the box. If 900 Watts is input, and 900 Watts goes out, the temperature inside the box, and the object inside, doesn't change.

 

[3DDave]

The heat loss happens at some temperature delta and some radiation amount. There is some transient heat storage in the mass in and of the box.

What was the basis for the loss estimate?