Selecting a windmill tower of the proper height provides maximum pumping capacity. Wind turbulence caused by trees, buildings and obstructions is likely to reduce the amount of water pumped and can cause problems for proper windmill operation. Windmills free from turbulence operate smoothly, have a longer, trouble free working life and receive better protection in strong storm conditions. Windmills with wind wheels from 8ft (2.4M) to 12ft (3.6M) in diameter should be at least 15ft above any obstruction within a 400ft (120M) radius. Higher is better. Larger windmills require additional clearance and should be at least 20ft (6M) or more above any obstruction within a 400ft (120M) radius. It is equally important that the area behind the windmill is also clear of obstructions.