Most NZ homeowners and landlords who have had heat pumps installed were never told what maintenance the units needed to get the most out of them. Nobody explains what happens on the inside when a unit never gets professional attention.
The answer is straightforward. Dust, grime, cooking oils, skin cells and pollen accumulate within both the indoor and outdoor units. That buildup starts a chain reaction that degrades the system's core ability to transfer heat and move air.
The indoor unit has a series of aluminium fins designed to transfer heat or cold to the air moving across them. The fins are thin and tightly packed together to maximise surface area in a small space. When dust and grime coat those fins, two things happen at the same time.
First, the layer of contaminants blocks the heat or cold from transferring efficiently to the air. The fins can't do their job because there is a barrier between the temperature source and the air that needs to absorb it.
Second, that same layer restricts the airflow moving across the fins. The gap between the fins is small, so when a layer builds up on them, less air gets pulled through, which means less heated or cooled air reaches your room.
The unit tries to compensate. The compressor runs longer and harder to reach the temperature you've set. You feel it as weaker airflow. The heat pump isn't blowing as hard as it used to.
The filter is a separate restriction point. When it becomes clogged, the unit chokes. It can't pull enough air into the system and push it out into your home.
The compressor works harder to try to achieve the set temperature, but the airflow constraint stops it from succeeding. You feel this as reduced output and longer run times. In a dusty home, or a home with pets or a kitchen nearby, the filter can become severely blocked in as little as eight weeks.
Cleaning the filter yourself every three to four weeks keeps this problem from developing. It doesn't address what's happening on the fins behind the filter. Those are a different problem.
The outdoor unit has the same fin structure as the indoor unit. Dust, pollen and outdoor contaminants coat those fins over time. Heat or cold transfer becomes less efficient. Airflow gets restricted.
Leaves, grass clippings and dirt can also accumulate around the casing of the outdoor unit. Debris around the casing restricts airflow in the same way a clogged filter does. A service that only addresses the indoor unit leaves the outdoor side of the problem unresolved.
Buildup happens in every home. Certain conditions make it happen faster.
A heat pump near the kitchen pulls in cooking fats and oils with every cycle. Running the unit with windows open draws in outdoor dust and pollution. Homes with pets, multiple occupants or smokers have more airborne particles circulating. Coastal properties face salt spray accumulation on the outdoor unit and on the indoor unit as well.
In any of these environments, the fins degrade faster than they would in a low-dust home with one or two occupants and no nearby cooking.
The compressor is the motor that drives the whole system. It sits inside the outdoor unit and its job is to move refrigerant through the circuit and do the work of heating or cooling.
When the fins are coated and airflow is restricted on both the indoor and outdoor sides, the compressor has to push harder against that resistance. It runs longer. It works at higher load. Every hour it operates under that strain, the internal components wear faster than they should.
This is what links a dirty heat pump to a shortened lifespan. The connection between unserviced fins and early compressor wear is direct. For more on what that means for how long a heat pump lasts, see the article on heat pump lifespan and maintenance.
You notice it as reduced performance. The unit doesn't heat or cool as well as it once did. It takes longer to reach the temperature you've set. The airflow feels weaker than it used to.
The reduction in performance is gradual, which means it often goes unnoticed until the system declines to the point where the homeowner thinks the unit is broken. More often than not, there is nothing mechanically wrong with the unit. It just needs a service to restore performance.
None of this is complicated. Dust and grime accumulate, block heat transfer and restrict airflow. Professional cleaning removes that buildup and restores the system's ability to do its job. If you're concerned about air quality inside the unit, not just efficiency, that's a separate issue covered in the article on mould in heat pumps.
The Home Energy Health Assessment takes about three minutes and tells you exactly what's happening inside your heat pump right now, and what needs attention. Take the assessment, free: assessment.miht.co.nz
There's no fixed timeline because it depends on the home. In a dusty environment with a filter that's never cleaned, you can feel the performance difference in as little as eight weeks. In a cleaner home where the filter is cleaned regularly, coil degradation takes longer but still happens over time. Year-round use without any professional attention makes 12 months a reasonable point at which efficiency has dropped noticeably. If you're not sure where your system sits, the Home Energy Health Assessment gives you a clear starting point.
The filter, yes. Cleaning it every three to four weeks is something homeowners can and should do. The internal coils are different. They sit behind the casing, require disassembly to access properly, and need specialist cleaning solutions and equipment to remove the compacted grime and organic growth on the fin surface. Attempting to clean them without the right equipment and products risks damaging the fins. Professional servicing is the only way to address coil buildup properly.
Yes. The outdoor unit has the same fin structure as the indoor unit and accumulates dust, pollen and outdoor contaminants in the same way. Heat transfer becomes less efficient and airflow gets restricted. Leaves, grass clippings and debris can also build up around the casing, which compounds the airflow problem. A complete service covers both units. Servicing only the indoor unit leaves the outdoor side of the problem unaddressed.
Cleaning the filter yourself keeps airflow moving through the unit and is worth doing every three to four weeks. It doesn't address what's happening on the fins behind the filter. Dust, cooking oils, moisture and organic growth accumulate on the internal coil over time in a layer the filter doesn't catch. A professional service removes that buildup from the coil surface, which restores heat transfer efficiency. The two tasks address different problems and both matter.
The most common signs are weaker airflow than the unit used to produce, longer run times to reach the temperature you've set, and rooms that don't heat or cool as well as they once did. The problem is that degradation is gradual, so it can be easy to accept as normal. If you're unsure where your system sits, the Home Energy Health Assessment gives you a clear picture of what's happening inside your heat pump and what, if anything, needs attention.
Your heat pump is doing one of two things right now. It's either running well, or it's working harder than it should to compensate for buildup you can't see. The Home Energy Health Assessment takes three minutes and tells you which. It covers your heat pump, ventilation and solar and it's free.