Usually the ducts and the grilles stay; the indoor and outdoor units, the controller and its cabling come new. Of the 112 registered ducted models in our catalogue, every one is on R32 or R410A, so an R22 system gets new pipes too. Here is what the code asks of a duct worth keeping, what the manuals say about pipes and returns, and how the new unit is matched to the old ducts.
Usually the ducts and the grilles; the rest comes new
When an old ducted system comes out, the parts in the roof do not all go with it. Our rule from the jobs we do: usually the ducts and the grilles carry over, and the controller and the cabling come new with the system, along with the indoor and outdoor units.
Daikin's ducted brochure lists the seven parts of a system: the indoor unit, the outdoor unit, the zone controller, the refrigerant pipes, the flexible duct, the supply air diffusers and the return air grilles. Here is how they usually fall:
| Part | Usually | Why |
|---|---|---|
| Flexible ducts | kept | if insulated and sealed to the code, they stay in the roof |
| Supply air diffusers | kept | sized to the rooms, not the unit |
| Return air grille | kept | unless the new unit wants a bigger return |
| Refrigerant pipes | depends | on the gas, the pipe size and the brand |
| Indoor unit | new | it is the system |
| Outdoor unit | new | it is the system |
| Controller and its cabling | new | they come with the system |
The ducts: insulated, sealed and dry, or they go too
A duct is worth keeping when it meets the code a new one would have to. The National Construction Code's housing provisions (13.7.4) set a minimum R-value on the duct material: R1.0 in climate zones 2 and 5 and R1.5 in zones 1, 3, 4, 6 and 7 for a combined heating and cooling system, with R0.4 on the fittings.
The same clause wants every joint and seam sealed to a Class C seal under AS 4254 (a draw band with sealant or tape on flexible duct), the insulation continuous from one duct to the next, and in a roof space an outer sleeve against damp, sealed with tape at least 48 mm wide.
Daikin's brochure puts the reason plainly: a roof can reach upwards of 80 degrees in summer, and up to 30 percent of the capacity delivered through a ducted system may be lost through the flexible duct network. So the roof-space photo is read for crushed runs, split jackets and joints hanging open before the ducts are counted as kept.
Our deep clean covers ducts vacuumed and leaky duct joints sealed, so a network that passes those checks is cleaned and sealed rather than replaced.
The grilles, and the return the new unit wants
Supply diffusers are sized to rooms, so they stay. The return air grille is the one to check, because it belongs to the unit as much as to the ceiling: it carries the filter (Daikin's brochure: a detachable filter to remove household dust), and the new unit's return has a size of its own.
- Mitsubishi Electric PEA, 10 to 16 kW: two 400 mm round return spigots
- Mitsubishi Electric large capacity, 20 and 24.5 kW: a 1,100 by 420 mm return
- Carrier QSH, 8.6 to 13.6 kW: an inlet flange of 1,145 by 334 mm; the 17 kW unit 1,188 by 385 mm
A bigger unit tends to want a bigger return, and when it does that is a new grille and a cut in the ceiling, which is why the ceiling shot goes with the quote photos.
The refrigerant pipes: it depends on the gas and the size
The 131 ducted models by registered refrigerant (catalogue, September 2026)
| Refrigerant | Models | Note |
|---|---|---|
| R32 | 100 | the current gas |
| R410A | 12 | the gas before R32; pipe re-use depends on the brand |
| no GEMS registration | 19 | no registered refrigerant to read |
| R22 | 0 | the gas in older systems |
Of the 131 ducted models in our catalogue, 112 carry a GEMS registration, and every one of them is on R32 (100) or R410A (12). None is on R22, the gas in older systems.
So a system old enough to be on R22 gets new pipes with the new unit. Between R410A and R32 it depends on the brand.
Mitsubishi Electric's ducted brochure describes a cleaning-free pipe re-use technology on its PUZ-ZM and PUZ-M outdoor units: a wide strainer catches iron particles from the existing pipework, which the brochure says may reduce the installation cost. The conditions are left to the dealer, so it is checked job by job.
Size matters as well. Mitsubishi Electric's PEAD installation manual specifies the pipe for each unit:
- 5 kW: 6.35 mm liquid and 12.7 mm gas
- 6 to 14 kW: 9.52 mm liquid and 15.88 mm gas
- both under 8 mm of insulation, bent no tighter than a 10 cm radius
Step from a 5 kW unit to a 7 kW one and both lines change diameter, so the old pipe does not carry over whatever gas it held.
The two units, the controller and the wiring come new
The indoor unit is the part the roof has to take. Mitsubishi Electric's PEA is built in two pieces so the heat exchanger and the fan deck go through the manhole separately, which its flyer calls ideal for remodelling existing houses; Carrier's 17 kW QSH splits the same way for renovation or retrofit work.
Daikin notes that its R32 ducted indoor units must sit in the ceiling space, not under a floor, so a system that lived under the house comes back as a roof-space job.
The controller is new because it belongs to the unit. Daikin's ducted range pairs with the BRC1E63 wall controller and the AirHub zone controllers; Mitsubishi Electric's with the PAR-41MAA and its zone controller; Panasonic's with the CONEX controllers. Each talks to its own indoor unit, so the old panel on the wall goes, with its cable.
Zoning is where a new controller earns its place. Daikin's AirHub reduces the indoor fan to between 60 and 100 percent of its nominal airflow as zones are turned off, and its OptiZone version regulates each damper and runs the fan between 30 and 100 percent to hold each zone's temperature.
The electrical side follows the unit: a new circuit sized to its breaker, and a check of the board's phase if the new unit is larger, which single phase or three phase covers. Our installation teams are licensed for that work.
Matching the new unit to the old ducts
The one figure that decides whether kept ducts suit a new unit is external static pressure: how hard the fan can push through the duct network. The ranges we install span a wide band:
| Range | External static pressure |
|---|---|
| Mitsubishi Electric SEZ, low profile | 5 to 50 Pa |
| Mitsubishi Electric PEAD | 35 to 125 Pa |
| Daikin FBA slimline | 150 Pa |
| Mitsubishi Electric PEA high static | 50 to 150 Pa |
| Carrier QSM | up to 160 Pa |
| Carrier QSH high static | 200 Pa |
| Mitsubishi Electric large capacity | 75 to 250 Pa |
A long network with many outlets needs the higher end (Carrier's brochure describes its high static QSH as for homes where ducts run to numerous outlets); a short one on a low-profile unit does not. The new unit is chosen against the duct layout, seen in the roof photo or on a site visit, not the other way round.
Ducted jobs take one to three days depending on size, zones and roof access, and the old system is decommissioned with its refrigerant recovered under our ARC licence. The ducted cost guide covers what each of those moves; send the roof-space and switchboard photos to start the quote.
Sources
- NCC 2022 Housing Provisions, 13.7.4 Heating and cooling ductwork: the R-values by climate zone, the Class C seal, the sleeve and the tape
- Daikin Ducted brochure: the seven parts of a ducted system, the 80 degree roof and the 30 percent duct loss, the ceiling-space note, the BRC1E63 controller, the AirHub fan ranges, the FBA's 150 Pa
- Mitsubishi Electric Ducted brochure 2025: pipe re-use on the PUZ-ZM and PUZ-M outdoor units, external static pressure by series, the PAR-41MAA and zone controller
- Mitsubishi Electric PEAD ducted installation manual: pipe diameters and insulation by unit
- Mitsubishi Electric PEA ducted flyer and Large Capacity ducted flyer: the two-piece construction, return air sizes, static pressures
- Carrier Ducted Systems brochure: QSM and QSH static pressures, the QSH170 split design, the inlet flange sizes
- Panasonic residential catalogue 2023: the CONEX controllers
- Our supply and install page (what carries over, one to three days, licensed electrical work, decommissioning) and deep clean page (ducts vacuumed, joints sealed)
- Our catalogue under ducted systems, 22 September 2026: 131 ducted models, 112 with a GEMS registration, 100 on R32 and 12 on R410A
