I want to absorb waste heat that is being collected (ducted) into an old industrial oven on its way out of a factory. As well as the heat that is ducted into the oven, the oven also has a thermostat that will maintain the oven temperature even though the heat exchanger absorbs heat from the air inside the oven.

The dimensions of the oven are in the sketch below.

I'd like to place the heat exchanger on a slightly elevated platform inside the oven so I'd like a heat exchange that is about 1000 X 1000 X 800 (L x W x H).

The temperature inside the oven will typically be around 150 degrees but it can exceed 220 deg C.

I'm hoping to absorb about 1MW of heat from the ovens, or as close to that as possible within the size limitation.

The water inside the tubes of the heat exchanger might be salty so the tubes of the heat exchanger should be either copper-nickel or stainless steel.