Fixed or variable speed pump (inverter)?
A fixed-speed pump always runs at the same speed, regardless of demand. A variable-speed pump (with inverter/VFD) matches its speed to actual need. The difference in consumption can be huge.
Why an inverter saves energy
The affinity laws apply: absorbed power grows with the cube of speed. Cutting speed by 20% can nearly halve consumption. In variable-flow systems (heating, boosting) the annual saving is often 30–50%.
Other benefits
- Constant pressure as demand varies (comfort).
- Soft starts: less water hammer and mechanical wear.
- Lower noise at part load.
When fixed speed is enough
If the load is constant 24/7, an inverter adds cost with little benefit. A well-sized fixed-speed pump is then the cheaper choice.
Grundfos models
The "E" versions (CRE, TPE, NKE, MAGNA3) have the inverter built in. Find the right models in the selector or among pumps for building and HVAC. See also our guide to EEI and IE efficiency classes.
Häufige Fragen
How much do you save with an inverter pump?
In variable-flow systems the annual energy saving is typically 30–50%, because absorbed power grows with the cube of rotational speed.
Is an inverter always worth it?
No: if the load is constant around the clock, a well-sized fixed-speed pump is cheaper; an inverter pays off when demand varies.