Heat pump installation mistakes: 12 issues that reduce efficiency

Short answer: Even a high-performance heat pump can perform poorly if the surrounding system is incorrectly designed or adjusted. The most serious problems are not always in the unit itself, but in sizing, water flow, operating temperatures, placement, frost protection and controls.

The complete system must be considered: building, heat pump, hydraulics, heat emitters, electrical supply and controls.

1. Sizing only by floor area

One of the most common oversimplifications is choosing a heat pump by applying a generic kW figure to a given floor area.

Two buildings with the same floor area may have completely different heat losses. Insulation, windows, air leakage, indoor temperature and local climate must be considered.

Correct selection starts with the heat-loss calculation, not floor area alone.

2. Oversizing “just to be safe”

A heat pump substantially larger than the building’s load is not automatically a safer choice. At low demand, the unit must be able to modulate its output down sufficiently.

If minimum output remains too high compared with demand, frequent compressor start-stop cycles may result.

3. Flow temperature higher than necessary

Heat pumps are generally more efficient at lower water temperatures. Permanently using an elevated flow-temperature setting can reduce seasonal efficiency.

Aim for the lowest temperature that maintains comfort under actual building conditions.

4. Weather-compensation curve disabled or incorrectly set

Properly configured controls can adjust water temperature to outdoor temperature. If the system runs at the same high temperature all the time, an important efficiency opportunity is lost.

Adjust the heating curve to the building and heat emitters; do not simply copy settings from another project.

5. Insufficient flow through the heat pump

Dirty filters, undersized pipes, partially closed valves, unbalanced manifolds or poorly selected circulation pumps can all reduce water flow.

Insufficient flow can cause large temperature differences, unstable operation and alarms. The hydraulics of the entire circuit must be checked.

6. Installing a buffer tank without knowing why

A buffer should not be added automatically. Determine whether it is needed for additional water volume, hydraulic separation, stable flow or a manufacturer’s specific requirement.

Unnecessary complexity can increase losses and lead to unwanted temperature mixing.

Read our separate guide to buffer tanks and heat pump hydraulics.

7. All heating zones can close simultaneously

In installations with many thermostats and actuators, consider what happens if nearly every circuit closes. The heat pump must still have the hydraulic conditions required for operation.

Thermostats alone do not solve this: zone control must be coordinated with the unit’s minimum flow requirement.

8. Inadequate frost protection

Where water circulates outdoors, particularly in many monobloc arrangements, frost protection is critical.

Do not rely on automatic circulation without assessing the possibility of a prolonged power failure.

See our guide to antifreeze and frost protection.

9. Poor outdoor-unit placement

The unit must be able to draw in and discharge air without significant recirculation. Observe the manufacturer’s minimum clearances.

A recess that is too enclosed or poorly placed obstacles can obstruct airflow.

10. No proper drainage for defrost water

At low outdoor temperatures, defrost cycles can produce water at the outdoor unit. It must be drained in a way that prevents troublesome ice build-up around the equipment.

A detail that seems minor in summer becomes very important in winter.

11. Checking the electrical supply too late

The heat pump’s thermal output is not its electrical input. Check maximum current, auxiliary heaters, protective devices and the power available from the building’s connection.

Ideally, these checks should happen before the equipment is ordered.

See our comparison of single-phase vs three-phase supply.

12. Commissioning ends when the compressor starts

Starting the equipment does not mean the system has been optimised.

Commissioning should include checking and adjusting flow, venting, temperatures, the heating curve, pump operation, domestic hot-water priority and zone-control logic.

What should be measured and recorded?

Depending on the system, record flow and return temperatures, water flow, relevant hydraulic pressures, key settings and how the installation behaves in different operating modes.

Such records are far more helpful for later troubleshooting than the general statement “the heat pump works”.

Can correct installation improve COP?

Installation does not change the unit’s inherent performance, but it allows the heat pump to operate under better conditions. An unnecessarily high flow temperature or incorrect water flow can make the system less efficient.

What do we check before selecting a system?

• the building’s heating demand;
• the required flow temperature;
• the output of radiators or underfloor heating;
• the system’s water volume and flow rate;
• the number of zones and how they are controlled;
• frost protection;
• outdoor-unit placement;
• the electrical supply;
• domestic hot-water demand;
• the manufacturer’s requirements.

Frequently asked questions

What is the most serious mistake?

There is no single answer, but sizing without calculating heat demand and constantly operating at excessive temperatures can undermine the entire system’s performance.

Can a good installer compensate for a wrongly selected heat pump?

An installer can optimise the system but cannot eliminate the limits of a seriously undersized or oversized unit.

Is following the manual’s standard hydraulic diagram enough?

The manufacturer’s diagrams are the starting point, but the version suited to the building’s actual configuration must be selected, and all conditions associated with that diagram must be met.

Further reading: the complete ECO-TEC guide or browse the available heat pumps.