How to calculate heat loss

I have a centrifugal water pump that I would like to protect during the winter months. The pipes can be drained, but there are some locations that are at risk for retaining trapped water, which can be problematic whenever we actually need to run the pumps. I am proposing that a heated enclosure be placed around the pump (see attached picture). However, I fear the exposed motor and the platform on which the pump sits will suck out a lot more heat than I anticipate. How can I accurately size a heater for this enclosure and take into account any conductive heat losses from these heat sinks? The platform is steel and the pump/motor are cast iron.



Thanks

Attached Images

pump heat.png (27.4 KB)