Does a ducted heat pump suit your house?
Consumer NZ says ducted systems have the least visual impact of any heat pump: no units on the walls, just small flush vents. They suit a household that wants bedrooms, hallway and living areas warm together, in a house with a roof space or subfloor an installer can actually work in.
Hiding everything has an efficiency trade-off. Consumer NZ says heat lost from the ducts makes these systems slightly less efficient than other types. BRANZ goes further: ducts that are overlong, full of bends or routed through uninsulated space can lose more than 30% of the heating energy.
A ducted heat pump isn't a ventilation system either. BRANZ says most recirculate the air already in the house with no fresh air coming in, so damp needs handling another way, through home ventilation for example.
How a ducted install usually runs
A heat load calculation, room by room
Mitsubishi Electric NZ says the quicker a home loses heat, the bigger the system has to be, and names insulation and orientation as the key factors. Black Diamond Technologies (BDT), which issues Mitsubishi Electric's NZ warranty, doesn't cover heat load calculations and excludes incorrectly sized systems, so the sizing rests with whoever designs the job.
Finding the spot for the indoor unit
BRANZ says the ceiling space is the best location, with the supply and return air ducts as far apart as possible. Consumer NZ says the unit can also go under the floor.
Running the ducts
Insulated ducts run from the unit to a vent in each room, and BRANZ says each room's share is controlled by its air flow. Short, straight runs inside the insulated part of the house waste the least heat.
Setting the outdoor unit
It needs open air around it and a spot away from bedrooms. The condensate drain (the pipe carrying water away from the indoor unit) needs its own route outside too.
Connection and paperwork
A registered electrician makes the connection, because it's prescribed electrical work. Expect a Certificate of Compliance (CoC) within 20 days of the work finishing, plus an Electrical Safety Certificate (ESC), and file both with the warranty papers.
What makes a ducted job bigger or smaller?
The number of rooms and vents is the obvious one. The space itself is the less obvious one. A roof space with room to move lets an installer keep runs short and straight. A low-pitched or skillion roof, or a two-storey house, can force longer, bendier runs or rule ducting out.
Electrical work can grow the job. If the switchboard needs changes, the EWRB says some work, especially on the main switchboard, main cable and main earth, must also be inspected by a licensed electrical inspector, which your electrician arranges.
Then there's access for the life of the system. BDT's warranty excludes extra costs from difficult or unsafe access, cranes and lift platforms included. LG's NZ warranty excludes extra costs for reaching units in restricted or unsafe spots above 2.4 m. MHIAA, the distributor for Mitsubishi Heavy Industries, says its equipment must be safely reachable with a 1.7 metre ladder.
Who can do which part, and is a consent needed?
Only a registered and licensed electrical worker can connect the system. Look them up on the EWRB's public register before work starts.
No government licence covers refrigerant work in New Zealand. Instead, an industry arrangement the Commerce Commission authorised in 2011 lets wholesalers restrict sales to people holding an RLTB Refrigerant Licence, or an EPA Approved Handler or Approved Filler test certificate. Ask the technician which one they hold.
Christchurch City Council says fixed electric heaters, heat pumps included, need no building consent if registered electricians install them and certify their own work. Exempt work must still meet the Building Code and the district plan, and in a unit title the body corporate's rules come first. Our consents and noise guide has more.
What's yours, and what's the installer's
You can
- Decide which rooms you want warm, and at what times of day.
- Find the roof space hatch and clear the way to it before the site visit. Leave the climbing to the installer.
- Keep the outdoor unit clear of plants, firewood and clutter.
- Once it's running, clean the return air filter as the manual says. Temperzone, for one, asks Hitachi owners to do this regularly.
Leave to a licensed installer
- The heat load calculation and the duct layout.
- All work in the roof space or under the floor.
- Refrigerant pipework, charging and commissioning.
- The electrical connection, the CoC and the ESC.
What a ducted quote should spell out
- The model, its heating capacity at 7 and 2 degrees, and how that was worked out for your rooms.
- Which rooms get a vent, and where the return air grille goes.
- Where the indoor unit sits, and how a technician will get to it later.
- Roughly where the ducts run, how they're insulated, and whether any cross unheated space.
- Zoning or room controls, if you want to heat parts of the house separately.
- Who issues the NZ warranty, how long each part is covered, and what servicing it needs. BDT, for example, lists its ducted kits and controllers at 1 year parts and labour, shorter than its split systems.
What we'd do
If it were our home
We'd only go ducted if the roof space lets the installer keep the ducts short, straight and inside the insulation. If the ceiling space is cramped or the house sprawls, we'd weigh it against a multi-room system before deciding. Either way, we'd want a ducted heat pump specialist up in the ceiling space before anything is quoted, rather than someone working from a floor plan.