A slinky loop is a variation of the horizontal ground loop and is used to maximize the effective heat transfer area of the excavation. The slinky loop gets its name from tying the pipe into large coils that overlap each other, allowing for large lengths of pipe to fit into much smaller trenches. For example, 800 ft. of ¾ in. pipe can be tied into a Slinky loop with 3 ft. diameter coils and be buried into a trench that is only 150 ft. long.
Slinky loops may be a little more economical than down and back horizontal loops because less trenching may be required, but more piping is needed for the same heating capacity. They area also easier to install because they don’t kink when putting them down in the trenches, and won’t spring up off the bottom of the trench.