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Most heat pump owners know roughly what a service involves. Filters out, internal components cleaned, outdoor unit checked. That covers a wall unit. A ducted system is a different piece of equipment, and servicing one is a different job.
A ducted heat pump doesn't sit on your wall. The main unit is installed in your ceiling cavity or under your floor, connected to every room through a network of flexible insulated tubing. Some installations run through the roof space. Others run under the house. Either way, the only parts you ever touch are the wall controller and the vents.
Everything else is hidden: the air handler, the internal coil, the drain pan, the ductwork, and every join holding it together. In zoned systems, the damper motors controlling airflow to individual rooms are up there too. When something starts going wrong in that space, nothing inside the house tells you.
NZ roof spaces aren't conditioned. In summer, the temperature inside a ceiling cavity can exceed 60°C on a dark roof. In winter, the same space drops to near outside temperature. Everything inside that space cycles through those extremes year after year.
Foil tape loses its grip in sustained heat. Flexible ducting becomes brittle. Drain lines that aren't properly supported start to sag and hold moisture. The electronics managing zone control and the communication between the indoor and outdoor unit sit in that environment year-round, and higher temperatures accelerate hardware failure.
A NZ roof space is harder on equipment than most homeowners realise, and the flexible ductwork used as standard here is the cheapest available option, not the most durable one.
Ducted systems in New Zealand use flexible insulated ductwork because it's cheaper and easier to install than rigid ducting. That's why it became the standard. It's also less durable.
The joins between duct sections are sealed with foil tape at installation. That tape loosens over time. When it does, conditioned air leaks into the ceiling cavity before it reaches the room. The system keeps running. The rooms still warm up. It just takes more power to get there.
That's The Set and Forget Cost at work in a ducted system. Invisible loss, no obvious trigger.
Loose joins aren't the only problem. Ducting hung from the ceiling can sag or drop. That restricts airflow to specific rooms. In roof cavities, rodents can tear through flexible ductwork entirely. Subfloor installations face additional ground moisture exposure. That shortens ductwork life. None of it shows up from inside the house.
A wall unit service takes 45 minutes to an hour. A ducted service takes one and a half to two hours. Here's what that time covers.
Roof cavity or subfloor access. The technician gets into the ceiling or under the floor to physically inspect the ductwork, check the drain line, and examine the joins. Insulation condition, moisture presence, and any evidence of rodent activity all get documented here. This part of the job has no equivalent in a wall unit clean.
Return air grille and plenum. Every bit of air in your home passes through the re
turn air grille and into the mixing box behind it before it gets reheated or recooled. Both collect dust and debris over time. A restricted return cuts airflow across the whole system. Both are cleaned on every visit.
Internal coil and drain pan. The internal coil is where the actual heating and cooling happens. Dust and organic material build up on the coil face over time. That layer sits between the coil and the air passing through it, so the system has to work harder to hit the temperature you've set. Below the coil, the drain pan catches moisture produced during cooling. On unserviced systems, that pan typically holds mould and sludge, and the drain line is often fully or partially blocked. A blocked drain line that overflows inside a ceiling cavity causes water damage that usually goes unnoticed until it shows on the ceiling lining.
Duct integrity check and joint sealing. Every accessible join gets inspected. There'll always be some leakage in a flexible duct system. On every visit, the job is finding how many gaps there are and how bad they are. Separated joins get resealed. Sagging sections get logged in the condition report.
Zone dampers. Where zone control is installed, each damper motor is cycled to check it opens and closes properly. A damper stuck open sends air to a room that doesn't need it. One stuck closed stops air reaching that room at all. Both show up regularly on systems that haven't been looked at for a few years.
Supply vents. Every ceiling vent in the house gets cleaned and cleared. Blocked vents reduce delivery at room level, and the central unit draws more power compensating for the restricted flow.
Outdoor unit. A wall unit has one outdoor unit cooling or heating one room. A ducted system has one outdoor unit carrying the load for every room in the house simultaneously. That's a significantly heavier workload, and it means the condition of the outdoor unit matters more. Dirt and debris on the condenser coil forces the compressor to work harder on every cycle. In coastal Auckland, salt in the air accelerates corrosion on the coil and cabinet. A neglected outdoor unit on a ducted system doesn't just affect one room. It affects the performance of the entire house. The condenser coil, the fan, and the clearance around the unit are all checked and cleaned on every service visit.
On a system that's never had a professional service, the pattern is consistent. Dust and grime on the return air filter, buildup on the internal coil, and mould or sludge in the drain pan. The drain line is often at least partially blocked.
Those internal conditions have outward signs. Rooms that take longer than they used to reach temperature. Uneven heating across the house. A stale smell on startup. A power bill that's crept up without an obvious reason. These aren't separate problems. They're the same problem showing up in different ways.
Loose or separated duct joins come up on nearly every first visit. In a lot of cases, at least one section has been sending a significant amount of conditioned air into the ceiling cavity rather than the rooms it was installed to serve. These systems don't suddenly fail. They run in a degraded state for a long time before anything becomes obvious.
Every one to two years, depending on how hard the system works and what the roof cavity conditions are like.
Ducted systems degrade faster than wall units between services. There are more components, more failure points, and a roof environment that does more damage than the inside of a heated room. In coastal Auckland, salt in the air adds wear to the outdoor unit, and annual servicing is the right call for those properties.
If a system has never been professionally serviced, a one-off restore is the right starting point. It establishes what you're actually working with, reseals what needs it, and clears the internal components. For ongoing care, an annual plan suits year-round use and a biennial plan suits seasonal or lightly used systems.
The return air filter is one part of the job. A full ducted service also includes getting into the roof, inspecting and resealing duct joins, cleaning the internal coil and drain pan, clearing the drain line, cycling the zone dampers, and cleaning every supply vent in the house. Cleaning the filter alone doesn't touch the ductwork, the drain system, or what's built up inside the air handler.
Usually, you can't tell from inside the house. A system with leaking joins still heats and cools. Uneven temperatures between rooms, higher power bills over time, and rooms that take longer to reach temperature are all possible signs. A roof cavity inspection is the only way to confirm.
A ducted service involves more components, takes longer, and requires getting into the roof or under the floor. The job takes one and a half to two hours compared to 45 minutes to an hour for a wall unit. The price reflects what's actually involved.
The process is the same regardless of brand. A professional ducted service should cover the same ground whether your system is Mitsubishi Electric, Daikin, Fujitsu, or Panasonic. The components are different, but the failure points are the same.
Both use flexible ductwork and a central air handler. The practical difference is access and environment. Ceiling cavity systems are reached through the roof space. Subfloor systems are accessed from outside or through an underfloor entry point. Subfloor installations typically face higher moisture exposure from ground conditions, which affects ductwork life and drain system performance over time. Both require the technician to physically get into the space to inspect the joins.
Not sure what condition your ducted system is in? The Home Energy Health Assessment takes about three minutes and shows you where to focus first.
Start the Home Energy Health Assessment