LF Bros N2 High Fuel Draw?

I recently bought an LF Bros N2 Heater for my RTT. I have it running at P1.4 (lowest setting) for around 10 hours a night and it burns through 3-4L of fuel. My tent is an oven all through the night while the outside temp is around 37 to 41 deg F. What could be the cause of the excessive fuel burn?