Ducted heatpumps are a thing here in NZ and make sense to me, not that I have used one. The heatpump sits in the roof and air is pushed into three or so rooms through ducts.
If building a new house I think ducts would be the way to go.
You have to think carefully about where you run the ducts. They can be a huge source of energy loss. 40% is the number quoted by the EPA.
Most roofs in Australia still aren’t sealed. The air barrier and insulation barrier is the ceiling. The roof space itself is not insulated, so the ducts are exposed to extreme temperatures, thus destroying the efficiency.
My argument with split systems, at least how they are installed in NZ, is that they are usually installed in the main living area and if there is a second unit, in a corridor.
So corridors are heated or cooled far hotter or colder than they need to be in order to heat/cool bedrooms.
I have two units that are heated by heat pumps in Massachusetts.
One has mini splits. You definitely don’t generally put mini splits in every single room (like bathrooms or interior hallways) because each mini split requires tubing, is large, and expensive. No, I think it’s way more likely that you would have them in the bedrooms rather than the hallway
That might be a climate difference — it gets below 0 Fahrenheit here every winter, as I understand it, NZ is quite a bit warmer, so maybe the strategy of “heat the core of the house and let it radiate out” works.
US and Australian units are different for insulation, but in my terms the insulation around the best ducts is R1.5, but good ceiling insulation is R6. 4x difference
Edit: not to mention the huge difference in surface area. Ducts can expose your conditioned air to a huge, poorly insulated surface. Bad for efficiency.
Interesting. The code for duct insulation in unconditioned spaces in the US is R8, and they're pushing for higher currently.
They also recently undid a long held myth about ducts buried in insulation leading to condensation issues. Most areas now allow ducts to be buried as long as you have R19 above and below, or R30 above. When I just installed a ducted mini for 3 upstairs bedrooms, I surrounded my R8 flex duct with R30 insulation.
Fwiw, context of this video is metal duct work. You’re not going to see R-8 flex duct buried in R-30 begin to sweat when the AC is running. In terms of controlling the dew point, the duct is no different than the conditioned space at that point.
Your statement is quite context dependent, and does not apply to most modern residential scenarios. “Over insulating” a flex duct is not going to cause condensation.
Metal duct work in an unconditioned space can cause condensation. Wrapping it in (often thin) fiberglass insulation can increase condensation in certain conditions. Improperly vented attics (and/or air leakage from conditioned space) with metal ducts can cause issues.
I thought this was absolutely the solution but backtracking a little now based on experience so far.
We have a two-level, five bedroom new build in Auckland which came with a single-zone ducted system. So outputs are the bedrooms plus upstairs and downstairs lounges. The vents are tidy and unobtrusive - much less space than a wall unit in each location.
We're having major issues balancing the temperature across the different rooms as there is one thermostat.
Think setting the temperature overnight for one room with a couple plus a cat vs another room with one of the kids. Basically the wife and I are always far too hot because otherwise we're freezing all the other rooms. Or setting a reasonable temperature in the lounge makes all the rooms icy in short time.
I'm now thinking about forking out the couple of thousand to get a small heat pump installed directly into our room so we can run it separately from the rest of the house.
So if building from scratch, either look into a multi-zone system or separate heatpumps. If you can get separate systems but hidden in the walls/roof that would be the best.
I had a similar problem, but I decided that simply running the fan to mix up the air was a fine solution. The fan doesn't use much electricity, and it's good not to let rooms get too stale anyway.
I have the fan programmed to run 10 or 15 minutes an hour regardless of if the heat pump needs to run. It keeps things pretty even.
Have checked the ducts for dampers? They're often installed where the duct branches. It's not unusual to find they're not balanced well or the locking screws have loosened allowing the dampers to move on their own.
always good to have zoning, either via small separate heat pump or with a retrofit like AirZone (not sure if something similar is available there) which modulates the flow to each duct from the air handler.
Ducted heatpumps are a thing here in NZ and make sense to me, not that I have used one. The heatpump sits in the roof and air is pushed into three or so rooms through ducts.
If building a new house I think ducts would be the way to go.