Hi I am planning to make a DIY heat exchanger. It will be an air-to-air counterflow heatexchanger with equal air flow. I made a small test heat exchanger so I would be able to estimate the required size of the heat exchanger. I did a small experiment with the small exchanger. The outcome is that with a 5 degree (Celsius) temperature difference between the cold air inlet and the warm air inlet, the warm air outlet cools down 1.3 degrees. Since I have equal airflow this means the cold air would be warmed up 1.3 degrees. I have a 9 square cm heat exchange surface (6 cm long x 1.5 cm broad). The question now is: what happens if I would double the length of the heat exchanger? Any help will be appreciated!