By SCWS Team
Published February 17, 2026 · 11 min read
You're in the shower, pressure's perfect—then someone flushes downstairs. The temperature spikes, the stream weakens, and you're left dancing around trying not to get scalded. Sound familiar? Constant pressure systems solve this problem permanently.
Traditional well systems cycle between cut-in and cut-out pressure—typically 40 to 60 PSI—creating noticeable pressure fluctuations. Constant pressure systems maintain steady pressure by varying pump speed to match demand. It's the difference between driving a car with cruise control and one where you're constantly adjusting the gas pedal.
Constant Pressure at a Glance
- How it works: Variable frequency drive adjusts pump speed to match water demand
- Pressure range: Maintains target pressure (typically 50-60 PSI) regardless of flow
- Energy use: 30-50% less during partial demand than conventional systems
- Pump life: 25-50% longer due to soft-start and reduced cycling
- Cost: $500-$1,200 more than conventional systems
How Conventional Systems Work (The Problem)
Understanding why constant pressure is valuable starts with understanding what's wrong with conventional systems. Traditional well pumps run at one speed: full blast or off. The pressure switch turns the pump on when pressure drops to the cut-in point (typically 40 PSI) and off when it reaches cut-out (60 PSI).
This creates two inherent issues:
Pressure fluctuation: Your pressure constantly swings between 40 and 60 PSI (or whatever your switch is set to). When you first open a faucet, pressure might be 55 PSI. By the time the pump kicks on, it's dropped to 40 PSI. Then it climbs back up while the pump runs. You feel this fluctuation as changes in shower pressure, flow rate variations, and temperature swings in mixtures of hot and cold water.
Pressure competition: Your pump delivers a fixed flow rate—say, 10 GPM. If someone runs a shower (2.5 GPM) and another person starts the washing machine (3 GPM) and then a toilet flushes (1.5 GPM), you're pulling 7 GPM. But if someone turns on the garden hose (5 GPM) at the same time, you're demanding 12 GPM from a 10 GPM pump. The result: pressure crashes for everyone.
How Constant Pressure Systems Work (The Solution)
Constant pressure systems use a variable frequency drive (VFD) to control the pump motor. Instead of running at one speed, the pump speeds up and slows down to match exactly what you need.
The Technology Behind It
A VFD (also called an inverter or variable speed drive) converts incoming AC power to DC, then regenerates it as AC at whatever frequency is needed. Since AC motor speed is directly related to frequency, changing the frequency changes the speed. This allows precise control from near-zero to full speed.
A pressure sensor monitors system pressure in real-time. When you open a faucet, pressure starts to drop. The controller responds by speeding up the pump just enough to maintain target pressure—say, 55 PSI. Open another faucet? It speeds up more. Close a faucet? It slows down. At zero flow, the pump may run at minimum speed or shut off completely.
What You Actually Experience
With constant pressure, your shower stays at the same pressure whether one fixture is running or five. You set your desired pressure (typically 50-60 PSI) and forget about it. No pressure swings, no temperature spikes, no fighting over who gets the good shower pressure.
Tankless water heaters love constant pressure systems. These heaters require minimum flow rates and pressure to fire—pressure fluctuations from conventional systems often cause them to cycle on and off during mixed use. Constant pressure provides the steady flow they need.
Real-World Example: A Ramona homeowner with four bathrooms and a pool was frustrated with pressure drops during morning routines. After installing a Grundfos SQE constant pressure system, they report steady 55 PSI whether one shower is running or all four bathrooms are in use simultaneously.
Benefits Beyond Steady Pressure
Energy Savings
Pump power consumption follows the affinity laws: power varies with the cube of speed. This means running at 50% speed uses only about 12.5% of full-speed power. During light use (a single faucet), your pump might run at 30-40% speed, using dramatically less electricity than a full-speed conventional pump cycling on and off.
Real-world savings depend on usage patterns. Homes with varying demand throughout the day see the biggest savings—30-50% less energy than conventional systems. Homes that typically use water in big bursts (everyone showers at the same time, then nothing) see less dramatic savings since the pump runs near full speed during use.
Extended Pump Life
Constant pressure systems protect your pump in two key ways:
Soft start: Instead of instantly hitting full power (which draws 4-7 times normal current), VFDs ramp up gradually. This eliminates the electrical and mechanical stress of hard starts. For a pump that might cycle 50+ times daily, this dramatically reduces wear on motor windings, capacitors, and bearings.
Reduced cycling: During moderate use, the pump runs continuously at low speed rather than cycling on and off. Fewer start/stop cycles mean less stress on all components. Many contractors report 25-50% longer pump life with VFD systems.
Low-Yield Well Compatibility
For wells with limited recovery rates, constant pressure is particularly valuable. You can set the pump to run at lower speed, matching the well's sustainable yield rather than outpacing it. This prevents the pump from drawing the well down and running dry—a common cause of pump failure in marginal wells.
Some controllers include low-water protection that automatically reduces speed if the well level drops, then gradually increases as the well recovers. This allows you to use a well that might otherwise be insufficient for a conventional system.
Popular Constant Pressure Systems
Franklin Electric SubDrive
The SubDrive is Franklin's flagship constant pressure solution, available in multiple models from 0.5 to 3 HP. It works with existing 3-wire Franklin motors in many cases, making it popular for retrofits. The controller mounts near your pressure tank and connects to a pressure transducer on the plumbing.
Features include soft-start, adjustable target pressure, dry-run protection, and diagnostic LEDs. The SubDrive Connect model adds WiFi connectivity for remote monitoring and alerts. Price: $600-$1,000 for the controller alone.
Grundfos SQE Series
Grundfos takes an integrated approach—the SQE pump has constant pressure capability built in, working with the CU 301 controller. This combination offers sophisticated pressure control, smartphone app connectivity (with optional module), and detailed operational data.
The SQE's permanent magnet motor is exceptionally efficient even at full speed, and the integrated design ensures optimal compatibility. The premium price ($1,200-$2,500 for pump and controller) reflects the engineering. Best for new installations rather than retrofits.
Pentair Intellidrive
The Intellidrive controller works with many standard submersible motors and offers straightforward constant pressure operation. It's positioned as a mid-range option with reliable performance and reasonable pricing ($500-$700 for the controller).
| System | Controller Cost | Retrofit Capable | Smart Features |
|---|---|---|---|
| Franklin SubDrive | $600-$1,000 | Yes (3-wire motors) | WiFi available |
| Grundfos SQE/CU 301 | $1,200-$2,500* | No (requires SQE pump) | App available |
| Pentair Intellidrive | $500-$700 | Yes (most motors) | Basic |
*Grundfos price includes integrated pump motor
Installation Considerations
New Installation vs. Retrofit
New installations are straightforward—you select a constant pressure system (either integrated like Grundfos SQE or a compatible pump with a VFD controller), install the pressure transducer on the plumbing, and configure your target pressure. The system works immediately.
Retrofits are more complex. Not all pumps are compatible with VFD operation. Two-wire motors generally don't work with aftermarket VFD controllers. Three-wire motors often work, but compatibility depends on age, condition, and specific motor characteristics. Have your system evaluated before purchasing a retrofit controller—an incompatible motor can be damaged by VFD operation.
Pressure Tank Size
Constant pressure systems need much smaller pressure tanks than conventional systems. Since the pump speed varies continuously to maintain pressure, the large drawdown capacity of a conventional tank isn't needed. A 20-gallon tank (or even smaller) provides enough buffer for the system to respond to demand changes.
This can be an advantage if you're replacing an old system with a failed large tank—you don't need to buy another giant tank. However, the tank still serves as a buffer when the pump is off, so some capacity is beneficial.
Electrical Requirements
VFD controllers require appropriate electrical supply and can be sensitive to power quality issues. Ensure your electrical service can handle the starting and running loads, and consider surge protection to protect the electronics. Installation should include proper grounding and may benefit from a dedicated circuit.
Is Constant Pressure Right for You?
Best Candidates for Constant Pressure
- Multi-bathroom homes: Where simultaneous use causes pressure competition
- Tankless water heater owners: Require steady flow and pressure
- Pressure-sensitive fixtures: Multi-head showers, body sprays, soaking tubs
- Low-yield wells: Where matching pump output to well recovery is critical
- Quality-conscious homeowners: Who value consistent water performance
- New construction: When choosing equipment anyway
When Conventional Might Be Fine
- 1-2 bathroom homes: Where simultaneous use is rare
- Budget priority: If cost is the primary factor
- Good existing system: If current pressure is acceptable
- Simple water use: Few fixtures, predictable patterns
Frequently Asked Questions
What is a constant pressure well system?
A constant pressure well system uses a variable frequency drive (VFD) to adjust your pump motor's speed based on water demand. Instead of running at full speed or off like conventional systems, it speeds up and slows down to maintain steady pressure—typically 50-60 PSI regardless of how many faucets are running.
How much does a constant pressure system cost?
The VFD controller adds $500-$1,200 to system cost depending on features and brand. Complete installed systems run $2,500-$4,500 including a compatible pump, controller, and small pressure tank. Retrofit controllers for existing pumps cost $600-$1,000 plus installation, though not all pumps are compatible.
Can I add constant pressure to my existing well pump?
Possibly. Some VFD controllers work with existing 3-wire submersible motors up to 2 HP. However, many pumps—especially older ones or 2-wire models—aren't compatible. The pump must be able to handle variable speed operation. Have a professional evaluate your current system before purchasing a retrofit controller.
Will constant pressure save energy and extend pump life?
Yes to both. Running at reduced speed during light use draws less power—potentially 30-50% savings during partial demand. The soft-start feature eliminates the high inrush current that stresses motors during startup. Less cycling and gentler operation can extend pump life by 25-50% compared to conventional on/off cycling.
Is constant pressure worth it for my home?
It's most valuable for homes with pressure-sensitive appliances (tankless water heaters, multi-head showers), multiple bathrooms used simultaneously, or low-yield wells where reduced pump speed helps match well recovery. If you have consistent pressure issues or hate the pressure drop when someone flushes, constant pressure is usually worth the investment.
Ready for Rock-Solid Pressure?
We install and service constant pressure systems throughout San Diego and Riverside Counties. Free consultations to evaluate if constant pressure is right for your well.
Call (760) 463-0493