Quick Answer
The recommended number of sprinkler heads per zone is 4-12 for residential systems and up to 30 for commercial systems. The number depends on water pressure, flow rate, and type of heads. More heads causes pressure drops, so zones should be designed to maintain optimal pressure.
When designing an in-ground sprinkler system, one of the most important considerations is determining how many sprinkler heads to put on each zone. The number of heads per zone affects water pressure, distribution uniformity, and more. Finding the right balance is crucial for an efficient system. This article will examine the key factors in choosing the number of heads per zone and provide guidelines for residential and commercial systems.
What is a Sprinkler Zone?
A sprinkler zone is a section of the system controlled by a single valve. When that valve opens, water flows through the supply pipes and is distributed to all the sprinkler heads on that zone. The heads are usually scheduled to run one zone at a time in a set sequence. Dividing an irrigation system into zones serves several purposes:
- It allows for customized schedules based on each zone’s watering needs.
- It prevents too many heads from operating simultaneously, which would cause pressure drops.
- It allows each zone to be shut off independently for maintenance.
- It enables separate programming based on sun exposure, plant types, and more.
Good zoning is critical for an efficient system. If one zone has too many heads, distribution will suffer. If zones are not logically divided, scheduling and adjustments will be more difficult. Finding the optimal sprinkler heads per zone involves balancing several factors.
Water Pressure Considerations
Available water pressure is one of the primary limiting factors for heads per zone. As more sprinkler heads run at once, the pressure drops. With too many heads, the pressure can fall below the optimal range, causing uniformity problems, misting, and poor coverage. Each additional head adds friction loss along the piping. Plus, most sprinklers require a minimum pressure (for example, 30 PSI) to achieve their designed spray pattern and flow rate. So how many heads can be safely added to a zone before pressures fall too low?
Static Pressure
The static pressure from the water supply must be taken into account. Municipal water pressure is typically 45-80 PSI. Well pressure can vary dramatically based on pump size, depth, and other factors. Higher static pressure allows for more heads on a zone because there is more pressure to start with before reductions occur.
Pressure Loss
Every foot of piping, elbow, valve, and other component causes friction loss that reduces pressure. The type and size of pipe also impact loss. Larger mainline pipes have lower loss. Friction loss intensifies as flow increases. Sprinkler heads at the farthest point will have the lowest pressure. Piping for zones should be designed to minimize losses and maintain adequate pressure across the full zone.
Elevation Changes
For sites with elevation changes, pressure varies at different head locations. Heads at the top have lower pressure. Pressure increases roughly 0.5 PSI for every 1 foot drop in elevation. Zones covering large elevation drops require special consideration to maintain higher pressure at the tops.
Water Supply Flow Rate
The available flow rate from the water supply is measured in gallons per minute (GPM). Flow rate capacity depends on the size of the supply pipe, well pump output, municipal water mains, and other factors. More sprinkler heads running at once requires higher flow. Each head has a rated flow, usually measured in GPM. Clumping too many high-flow heads can exceed the available supply. Flow rate must be balanced across zones.
Guidelines for Residential Systems
For residential in-ground systems, a general guideline is 4-12 sprinkler heads per zone. Here are some common residential zoning configurations:
4-6 Heads Per Zone
Zones with just 4-6 heads are common for residential systems. This provides the best pressure and optimal sprinkler performance. It allows a greater number of zones for customized watering. But it requires more valves and electrical connections. Only small areas can be covered per zone.
7-12 Heads Per Zone
Most residential controllers have capacity for 6-12 zones. Having 7-12 heads per zone is a good compromise between coverage and pressure. These medium-sized zones can operate efficiently on typical residential water supply. Pressure losses are still manageable with good design.
15 Heads Per Zone (Maximum)
In some situations, larger zones with 13-15 sprinkler heads may work. This should be the upper limit for residential systems under ideal conditions. Pressure losses start to become significant and distribution problems arise. Only use this many heads where static pressure is high, distances are short, and piping is optimized.
Factors in Residential Zone Size
To choose the best zone size for a residential system, consider these factors:
- Water pressure – Prioritize keeping zones under 80 PSI pressure loss for optimal performance.
- Zone width – Narrower zones of 15-30 feet are best to limit distance from valves.
- Head types – Use lower flow heads rated at 1.5-3.0 GPM to allow more per zone.
- Piping – Choose 1″ poly or PVC lines to minimize friction loss.
- Valves – Quality zone valves reduce pressure losses.
Also balance zone size with the number of zones needed for scheduling flexibly. Keep similar plant types on the same zone. Break up areas with different sun exposures or water needs.
Guidelines for Commercial Systems
Commercial irrigation systems allow for larger zones with more heads. This is due to higher static water pressures and flow rates available. It also minimizes the number of zone valves required. Here are some typical commercial zone configurations:
20-30 Heads Per Zone
Commercial sites often create zones in the 20-30 head range. At this size, pressure losses can still be mitigated with proper design and good pressure regulation. These medium zones provide flexibility without requiring huge flow rates or too many control valves.
30-50 Heads Per Zone
For very large commercial sites, such as golf courses, zones can sometimes go up to 50 heads or more. This requires high-capacity pumps and mainlines to deliver adequate pressure and flow. Careful hydraulic calculations are needed to prevent low pressures at distant points.
Factors in Commercial Zone Size
To maximize commercial zone size while maintaining efficiency, follow these guidelines:
- Static pressure – Over 80 PSI is recommended for larger zones; 100 PSI optimal.
- Supply rate – Minimum 60 GPM for 50-head zones; allow for peak flow rates.
- Mains – Large 4″ or 6″ mainlines prevent major friction losses.
- Pressure regulation – Use regulators at valves to ensure minimum pressures met.
Also divide commercial zones based on plant water needs, sun exposures, and control requirements just like residential zones.
Pressure Regulation
To ensure proper pressures across zone piping, pressure regulation devices are recommended. Here are two types:
Pressure Reducing Valves
PRV valves installed at zone valves reduce incoming supply pressure to a preset lower pressure. This compensates for friction loss and ensures steady pressure to sprinklers across the zone. Most can be adjusted from 25-75 PSI.
Pressure Compensating Emitters
Some micro-irrigation heads and nozzles for drip/bubbler systems feature pressure compensation. These regulate outlet flow to remain constant across a wide range of pressures. They help normalize pressure differences between heads.
Low Pressure Options
If low water pressure is a limitation, choosing lower flow/pressure sprinklers can allow more heads per zone. Some options include:
- Rotary nozzles – Require only 30 PSI and spray 0.5-2.2 GPM
- Micro-sprays – Cover 5-15 feet radius at 15 PSI and 5-20 GPM
- Subsurface drip – Needs only 10 PSI for low flow emission
Converting existing fixed spray heads to lower pressure rotary or micro-sprays allows fitting more heads per zone.
Zone Valve Selection
The valves controlling each zone also impact performance. Features to look for include:
- 1″ or larger ports for maximum flow
- Durable diaphragms and seals
- Low friction loss ratings
- Flow control adjustments
- Fast opening/closing
Quality zone valves minimize pressure losses and downtime for repairs. Consult manufacturers’ friction loss charts when selecting valves.
Designing For Uniform Coverage
In addition to pressure, choosing the right number of heads per zone also ensures uniform water coverage across the zone. Differences in pressure between heads can lead to uneven distribution. Here are some tips:
- Use matched precipitation rate sprinklers
- Overlap spray patterns correctly
- Consider repeating head types for consistency
- Locate heads away from edges to avoid dry spots
Proper spacing, pressure regulation, and zoning prevent coverage gaps between heads on the same zone.
Zone Mapping
When designing zones, create a clear map showing the layout. This allows you to:
- Balance flow rates across valves
- Identify high and low pressure points
- Divide zones by plant type or microclimate
- See coverage of head spray patterns
- Calculate zone size
Mapping helps optimize the number of heads per zone before installation. It is also useful for diagnosis and renovations later on.
Zone Pressure Testing
After installation, test zones separately to profile the pressure across the system. Attach pressure gauges at valves and ends of lines. Turn zones on one at a time and record pressures. Look for problem areas to address:
- Pressure below optimal range at heads
- Inadequate pressure differential from valve to end heads
- Excessive pressure losses along lines
Testing validates design and identifies modifications needed, such as reducing heads per zone, upsizing pipes, or adding regulation.
Conclusion
Choosing the right number of sprinkler heads for each zone is critical in irrigation design. Consider all the factors of water supply, pressure losses, elevation, and flow rates. For residential systems, 4-12 heads per zone is recommended, up to 15 under optimal conditions. Commercial sites can often accommodate 20-50 heads with proper supply and mainlines. Use pressure regulation, low pressure heads, and good zone valve selection to maximize zones. Map out zones and test pressures for best results. With a well-designed number of heads per zone, in-ground sprinkler systems can operate at peak efficiency.
