Does anyone have the formula or procedure to calculate this CSA requirement? I would rather not recreate a wheel. Thanks, 220.127.116.11 Heat transfer between supply and return pipes should be examined as part of the piping distribution design. The heat gain (loss) between horizontal pipes serving the building from the heat exchanger shall not lose more than 5% of the proposed energy transfer under full load conditions. Pipes should be separated for physical installation reasons such that the minimum spacing is 15.2 cm (6 in).