Condensate Pumps Explained
Condensate pumps move condensate from low points back to the boiler house. Learn about electric condensate pumps, steam-powered pumps, and how to size and select the right pump for your system.
When You Need a Condensate Pump
If condensate can flow by gravity back to the boiler house, no pump is needed. But when equipment is below the level of the condensate receiver, or when return lines are too long for gravity flow, a condensate pump is required.
Condensate pumps are also needed when the condensate return pressure is too low to overcome the boiler feedwater tank pressure. The pump boosts the condensate pressure to deliver it to the tank.
Types of Condensate Pumps
- Electric centrifugal pumps: Most common type. A float switch in the receiver tank starts and stops the pump automatically. Compact, reliable, and efficient for most applications.
- Steam-powered (pressure-powered) pumps: Use steam pressure to push condensate. No electricity required. Ideal for hazardous areas or locations without power. Can handle high temperatures and flash steam without cavitation.
- Receiver pump sets: A packaged unit containing a receiver tank, one or two electric pumps, and controls. Standard solution for collecting and pumping condensate from a zone or building.
Sizing Considerations
- Flow rate: Size the pump for the maximum condensate generation rate, with a safety factor of 1.5 to 2x for peak loads and warm-up conditions.
- Head pressure: Must overcome the height difference to the receiver tank plus pipe friction losses plus the tank pressure (if pressurised).
- Temperature: Condensate may be near boiling point. The pump must handle hot water without cavitating. Consider NPSH carefully.
- Flash steam: Condensate at high temperature will flash when it enters the low-pressure pump suction. Pump design must handle two-phase flow or a degassing tube must be installed.
Cavitation risk
Condensate pumps are prone to cavitation because the water is near its boiling point. Ensure the pump has adequate NPSH margin. Install the receiver tank above the pump suction and keep suction piping short and large diameter. See our Pump NPSH Explained guide.
Installation Best Practices
- Install the pump below the receiver tank to provide positive suction head.
- Use a strainer on the pump suction to catch debris.
- Install a check valve on the discharge to prevent backflow when the pump stops.
- Provide a bypass line so the pump can be isolated for maintenance without stopping condensate return.
- Install a vent pipe on the receiver to release flash steam safely.
- For electric pumps, use a float-controlled auto-start system with a high-level alarm.