The bottom of the greenhouse allows for the maximum height differential between collector and tank and is the most convenient location for the collector fins. 

The tank must be higher than the collectors.  The cold outlet from the tank should be at least 18” above the top pipe of the heat absorber to avoid back flow at night.  This is the rule for greenhouses and also the placement of tanks above Big Fins placed in skylights.

Big Fin absorbers should face towards the south with a lee-way of 30º east or west of south and the tilt should be the latitude with a lee way of plus or minus 15º.

Example:  If your latitude is 40º the absorber can be tilted to the south at an angle between 25º and 55º below horizontal.

Vertical glass is OK for winter space heating but not year round water heating.  If you are installing Big Fin behind existing vertical glazing, you must place a reflector outside in front of the Big Fin to direct summer sun onto the array.