Feet of head is a term used in pool system design to calculate the amount of resistance to water flow in your pool system. The more resistance the higher the feet of head. In technical terms, feet of head equates to the height of a column of water that a pump can maintain at full operation. In-ground pool pumps are designed for High Head or Medium Head operation. High Head pumps will handle more resistance (maintain a higher column of water); Medium Head pumps will handle lower levels of resistance. This guide discusses the basic differences in design of High Head and Medium Head pumps and compares the performance of several popular High Head and Medium Head pumps.
Note: Click on the picture to enlarge the graph.
RESISTANCE FACTORS - There are several factors in the design of a pool system that generate higher resistance to water flow: Chief among these are: the diameter of the system piping - a smaller diameter (1 1/2") will generate more resistance than a 2" or 2 1/2" diameter pipe: The distance of piping between the pool and the pump; the elevation of the pump above the pool surface; the number fittings in the piping between the pool and the pump; the type of fittings used - a single 90 degree elbow will have more resistance than two 45 degree elbows; the number of water features; and the use and height of solar panels. A pool system with several of these factors will generally require a pump with a high head design.
HIGH HEAD DESIGN - High Head pumps are designed for greater performance and efficiency. A standard 1 HP High Head pump will outperform a 1 HP Medium Head Pump due to several design upgrades including: the addition of run capacitors These capacitors smooth out the variations in the alternation current during operation which helps reduce heat loss in the windings. Many of these pumps also have heavier wire in the windings to also reduce electricity wasted from heat loss.
MEDIUM HEAD DESIGN - The older Medium Head Pump designs, like the popular Hayward Super Pump, are used in basic pools with simple piping and lower head. They generally are designed with only start capacitors or no capacitors and offer a less expensive option for a pump.
BASIS FOR COMPARISON - We will compare each pump's performance in GPM as shown in their performance curves like the one in this picture. To ensure that we are comparing like pumps, all pumps selected will be standard up rated pumps with similar total HP (THP) - THP is the product of HP x Surface Factor (SF). All the pumps selected have THPs of between 1.10 and 1.25. The Feet of Head will be arbitrarily selected at 50'.
SELECTION OF DATA - This chart shows how a pump's GPM performance is determined based on a Feet of Head of 50'. The curves labeled E, F, G, H represent the performance curves for Pentair WhisperFlo High Performance pumps with THP of 0.93, 1.25, 1.65 and 2.20 respectively Since we are comparing pumps with close to 1.25 THP, we will select curve F. This is the performance curve for a Pentair WhisperFlo WF-24 model pump. Now we look for where the line for 50 feet of head intersects with the F curve (circled in red). Drop straight down from that intersection to get a water flow of about 68 GPM.. In summary, the performance of a WhisperFlo High Performance single speed uprated pump with a THP of 1.25 is 68 GPM. The Performance data for all other pumps shown in the table below was extracted in a similar manner.
PUMP COMPARISON - This chart compares the GPM performance of some of the more popular High Head and Medium Head pumps. All pumps are equivalent in THP (between 1.1 and 1.25 Total HP) and their relative GPM water flow is measured at 50 Feet of Head resistance. The table show a comparison of GPM performance for 6 High Head (HH) and 2 Medium Head (MH) pumps. By comparison the 6 HH pumps generate between 55 and 70 GPM at 50 Feet of Head. The 2 Medium Head pumps generate 40 GPM at 50 Feet of Head, Keep in mind that these are performance numbers for specific models of each pump. The do not represent the performance of all models of that pump.
ABOVE GROUND PUMPS - As a side note, High Head and Medium Head pumps are generally designed for in-ground pools with measurable head. Above ground pumps have minimal head since they are only pulling and pushing water through short hoses between the pool and the pump. Most AG pool pumps are therefore designed for Low Head with considerable cost savings.