At minimum, the gallons per hour (GPH) rating should match the volume of your pond. A pump will need additional GPH to supply a waterfall or fountain, and enough "head" to push water to the top of that waterfall or fountain. Look for the unit with the lowest wattage; it will cost the least to run.Direct drive
These heavy-duty units, which were the first pond pumps, are able to move lots of water. They also use the most power, and if their seals fail, they can spill oil.
Head: up to 52 feet.
Warranty: one to two years.
Cost: $200—$1,400. PondScapeOnlineMagnetic drive
Much cheaper to buy and operate than direct drives but without nearly as much oomph.
Head: up to 15 feet.
Warranty: six months to three years.
Cost: $45—$300. Danner Manufacturing, Inc.Hybrid drive
Combines the power of a direct drive with the energy efficiency of a magnetic drive. Won't spill oil.
Head: up to 25 feet.
Warranty: two years.
Cost: $185—$500. Atlantic Water Gardens