Avoid These Common Heat Pump Installation Mistakes

Editor's Note: This article was first published on July 23, 2024 and refreshed on August 8, 2025 to provide the most current and comprehensive information on heat pump installation mistakes.

In New Zealand, heat pump systems are well known for their effectiveness and environmentally responsible heating and cooling features. They provide both warm and cool air from a single unit by moving heat from one place to another. However, the installation of a system has a significant impact on its longevity and efficacy. Numerous issues, such as decreased efficiency, increased energy costs, and frequent malfunctions, can result from a poorly installed heat pump.

Having serviced thousands of heat pumps nationwide over the years, OneAir has an unmatched grasp of what makes an installation right—and, more crucially, what doesn't. Since our technicians are regularly called in to address problems resulting from improper installations, we have direct knowledge of the most typical pitfalls. 

What happens when you install a heat pump incorrectly?

Incorrect heat pump installation can lead to high energy bills and frequent breakdowns. Correct sizing, proper placement, and professional wiring are crucial for efficiency. Always hire a qualified installer who follows manufacturer guidelines and conducts a thorough commissioning process. Regular maintenance also helps ensure long-term performance.

Top 10 Common Heat Pump Installation Mistakes

1. Incorrect Sizing: A Mismatch for Your Home

One of the most frequent mistakes in heat pump installation is incorrect sizing. A heat pump must be precisely sized to meet the heating and cooling demands of the specific space. Beyond basic size calculations, many installers fail to account for a home's insulation levels and solar gain. A home's insulation is key to a heat pump's efficiency. If a property isn't well-insulated or has gaps and leaks, the heat pump will work overtime to maintain the set temperature, leading to increased energy use and higher utility bills.

• Undersized Unit: An undersized unit will struggle to reach the desired temperature, causing it to run constantly. This leads to premature wear and tear, higher energy consumption, and poor comfort.

• Oversized Unit: An oversized unit will cycle on and off too frequently. This "short-cycling" is inefficient and can shorten the equipment's lifespan.

2. Poor Placement: Location Matters

Proper placement of both the indoor and outdoor units is critical. The outdoor unit needs adequate airflow, requiring at least 150mm of space from the wall behind it and 500mm of clearance in front, free from obstructions like plants or debris. Placing a unit too close to a wall restricts airflow, reducing efficiency and potentially causing excess noise for neighbors. In areas prone to sea spray or sulfur, a special coating may be required to protect the unit and maintain warranty coverage. The indoor unit should be strategically placed to ensure optimal air distribution. Installing it in a kitchen, for example, is a mistake, as cooking oils in the air can significantly degrade performance and lifespan.

3. Poor Wiring: A Serious Safety Hazard

Improper wiring and electrical connections are a significant safety risk, with the potential for electrical fires. It's mandatory for a licensed electrician to perform all electrical work, ensuring compliance with local codes. The heat pump should be connected to a dedicated circuit to prevent overloading the electrical system. The correct wire size must also be used, with larger heat pumps or long wire runs often requiring 4mm or 6mm cable.

4. Refrigerant Issues: The System's Lifeblood

The refrigerant charge must be precisely calibrated. An incorrect charge can lead to reduced efficiency, higher energy bills, and system damage.

• Too much refrigerant: Can cause dangerously high pressure within the system.

• Too little refrigerant: Leads to insufficient heating or cooling and can severely damage the compressor—the most expensive part of the heat pump.

A common oversight is failing to add more refrigerant for pipe runs longer than 10 meters, which can lead to system breakdown and costly repairs.

5. Poor Ductwork Design: The Ducted System's Weak Link

For ducted heat pump systems, ductwork design is paramount. Poorly designed ductwork can lead to increased pressure, insufficient airflow, and reduced efficiency. Common issues include:

• Extended duct runs, sharp bends, and excessive branching: These create resistance, making it harder for the heat pump to distribute air and resulting in uneven temperatures and increased energy use.

• Leaks and inadequate sealing: Leaky ducts can lose up to 30% of conditioned air, reducing efficiency and spiking energy bills. Properly sealing all connections is vital.

• Incorrect duct sizing: Ducts that are too small restrict airflow, forcing the system to work harder. Conversely, ducts that are too large can lead to poor air velocity and uneven distribution.

• Insufficient return air: Proper return ducting and grille sizing are crucial for the system to circulate air effectively.

6. Drainage and Ventilation Problems

Proper condensate drainage is essential to prevent water damage and mould growth. The drain line must be sloped correctly to ensure water flows away from the unit. Regular maintenance can prevent clogs and sludge buildup. Insufficient ventilation can also impact performance by allowing pollutants and moisture to accumulate, affecting both indoor air quality and the heat pump’s lifespan.

7. Operational and Performance Issues

Incorrect thermostat placement and settings can significantly impact performance. The thermostat should be placed in a central location that accurately represents the home’s average temperature, away from direct sunlight, doors, or windows. Setting extreme temperatures (e.g., 16°C for cooling or 27°C for heating) forces the system to work harder, consuming excessive electricity and struggling to reach the target.

Ignoring manufacturer specifications is a major oversight. Failing to follow these guidelines and use recommended components can lead to system damage and inefficiency.

8. Using Low-Quality Installation Materials

The quality of installation materials matters. Opt for materials from reputable electrical or specialist HVAC suppliers. For outdoor components, stainless steel screws are a must to prevent rust. Installers should use silicone sparingly and ensure all wiring offcuts and debris are properly cleaned up.

9. Improper Evacuation of Pipework

Before a heat pump is turned on, technicians must use a vacuum pump to evacuate the pipework, removing all air and moisture. Failure to do so can lead to premature system failure. A digital gauge should be used to confirm that the pressure has reached 200 microns or less.

10. Skipping the Commissioning Process

A thorough commissioning process is the final, critical step. This post-installation check ensures all components are functioning correctly and that the system operates within manufacturer parameters. This includes verifying the refrigerant charge, electrical connections, airflow, and overall system performance.

The Long-Term Consequences of a Bad Installation

The repercussions of a poor installation are significant and costly.

• Higher Energy Bills: A poorly installed heat pump can be up to 30% less efficient, leading to a noticeable increase in your monthly power bills.

• Reduced Lifespan: The added strain on the system from issues like incorrect sizing or placement results in premature wear and tear, leading to more frequent breakdowns, expensive repairs, or even shortened lifespan of your heat pump.

How to Ensure a Proper Installation

To avoid these common pitfalls, it is crucial to hire qualified, experienced professionals. In New Zealand, while specific qualifications aren't strictly mandated, reputable installers like OneAir have the knowledge and expertise to ensure your heat pump is correctly sized, placed, and installed according to manufacturer guidelines and local codes. Always check references and reviews, and ask if the technicians have attended manufacturer training to stay up-to-date on evolving technology and regulations.

Following manufacturer guidelines and adhering to a regular maintenance schedule are also essential for long-term performance. Routine inspections and servicing can catch potential problems before they become serious issues, protecting your investment.

Below is a simple checklist to ensure a proper heat pump installation:

Ready for a Heat Pump Installation You Can Trust?

Correct heat pump installation is foundational to its efficiency, performance, and longevity. By avoiding common mistakes—such as incorrect sizing, poor placement, and inadequate insulation—you can prevent numerous problems, from increased energy bills to frequent maintenance issues. Choosing certified professionals, following manufacturer guidelines, and maintaining your system are the key steps to enjoying the full benefits of an effective and efficient heat pump system.

---

Five Frequently Asked Questions About Heat Pump Installation:

Q: How long does a heat pump installation typically take? 

A: A standard back-to-back heat pump installation typically takes between 2 to 4 hours. However, more complex installations involving longer pipe runs or ducted systems can take a full day or more.

Q: What are the signs of a poorly installed heat pump? 

A: Common signs include uneven heating or cooling, unusually high energy bills, excessive noise from the unit, frequent cycling on and off, or water leaking from the indoor unit.

Q: Is it important for an electrician to install a heat pump? 

A: Yes, all electrical work for a heat pump installation must be performed by a licensed electrician to ensure safety and compliance with local codes. Incorrect wiring can be a significant fire hazard.

Q: Why is a heat pump's size important? 

A: Sizing is crucial because an undersized unit won't effectively heat or cool your home, while an oversized unit will short-cycle, both of which lead to inefficiency, higher bills, and a shorter lifespan for the equipment.

Q: What is "commissioning" in a heat pump installation? 

A: Commissioning is the final, comprehensive check performed by a professional installer after the physical installation is complete. It involves verifying the refrigerant charge, electrical connections, airflow, and overall system performance to ensure it's operating correctly.