The heat dissipation for MVI56, MVI56E, MVI69, MVI46 and MVI71modules is as follows: The power ratings label states that the maximum current drawn from the ControlLogix backplane is 800 ma at 5.1 VDC, 4.08 watts.
If you want to convert this to BTU/hr. you would multiply the power dissipation by 3.413, or 13.925 BTU/hr. Using the information noted above if you power the device for one hour it will generate 13.925 BTU of heat.
To convert BTU to joules, multiply by 1055. Therefore 13.925 BTU equals 14,691 joules.