Best home heating system?

Forums › Home Workshop DIY › Best home heating system?

1 | 2 | 3 | 4

20859 posts

Uber Geek
+1 received by user: 5350

Trusted

Lifetime subscriber

#3379320 30-May-2025 22:03

I can't comment on prices, except to say it's likely a lot less than a ducted system with per-room temperature controls. I will ask though, do any of the rooms such as north facing rooms ever need cooling while the others need heating? In that case you might two outdoor units, one feeding north facing rooms, one feeding south facing.

Stu1

1892 posts

Uber Geek
+1 received by user: 489

ID Verified

Subscriber

#3379325 30-May-2025 22:45

benz1:

timmmay:

Suggest you find an experienced installer who knows their stuff. High volume doesn't always mean they know anything. Anything you read online take with a grain of salt - especially what I say :)

I suspect heat pumps put out air that's not as hot as gas systems, so you need higher volumes of air. Higher volume of air through a narrow duct means noise, or you may not be able to push enough air through. I think most rooms have 200mm ducts in our ducted system, from memory, 250 to the lounge before it splits, and the return is 300 or 400mm - not sure.

If you asked my wife she'd say she'd never have ducted again. Individual room units do have their advantages, not having to deal with returns or such would be helpful. If I was starting again I'd think hard about whether to do ducted or high wall / floor units. The ducted works fine in most cases, but things like diffusers pushing the air in at the ceiling and the return being at the ceiling doesn't work great, you want to draw air across a room rather than blow it around.

Apologies for resurrecting an old post but I've sat on this for months and done nothing about it due to indecision! But now, my existing sole 9kW heat pump has packed up and is being replaced by a shiny new Mitsubishi Electric AP80 9kW unit so it has encouraged me to sort this out once and for all.

timmmay has managed to talk me out of going for a ducted system, just seems too complicated with too many variables and too much reliance of finding a good installer. So I'm looking at installing a Mitsubishi Electric multiroom system with 5 indoor units (in 3 bedrooms, kitchen/diner and study), (3 x AP25 3,2kW & 2 x AP35 3.7kW) connected to a 5F100 10kW outdoor unit. I've been advised that this will be enough as only a couple of the indoor units would ever be on at the same time.

So my question to those a lot more knowledgeable than me, does this seem like a reasonable solution to avoid a ducted system? I've been quoted $10,650 installed which is a combination of lower prices on the indoor units and price matching the outdoor unit. Does this sound reasonable? Many thanks.

I was recently quoted 10k for three indoor units in three bedrooms 7kw heating and 5 k cooling Mitsubishi . Looked at full ducted 23k for 150sqm . This was through the recommend installer for Mitsubishi in welllington .I will stick with my gas central heating for now and hope hydro gas comes in at some point . Gas is such a nicer hear than heat pumps

tweake

2647 posts

Uber Geek
+1 received by user: 1139

#3379352 31-May-2025 11:07

timmmay:

I can't comment on prices, except to say it's likely a lot less than a ducted system with per-room temperature controls. I will ask though, do any of the rooms such as north facing rooms ever need cooling while the others need heating? In that case you might two outdoor units, one feeding north facing rooms, one feeding south facing.

this is a good point. especially with upstairs and downstairs.

tweake

2647 posts

Uber Geek
+1 received by user: 1139

#3379354 31-May-2025 11:22

benz1:

So I'm looking at installing a Mitsubishi Electric multiroom system with 5 indoor units (in 3 bedrooms, kitchen/diner and study), (3 x AP25 3,2kW & 2 x AP35 3.7kW) connected to a 5F100 10kW outdoor unit. I've been advised that this will be enough as only a couple of the indoor units would ever be on at the same time.

thats not really true, a bit of salesmanship there i suspect. they do run at the same time, in fact its better they do. 10kw for a 180sqm in auckland sounds way to small, but it does depend on the house. i highly recommend running your house specs through a heating calc.

also, unless your outdoor space is limited, i recommend multiple outdoor units. as mentioned hot side of the house (or top floor) may need cooling while cold side needs heating. plus multi head units tend to run less efficient especially when only a few heads are running (the less that run at once the worse it gets and this is probably why they are under sizing the outdoor unit so much.). then there is redundancy, if single out door unit fails then you loose everything.

i would look at having an outdoor unit per floor, especially as a lot of people prefer bedrooms to be colder than living room.

Handle9

11927 posts

Uber Geek
+1 received by user: 9683

Trusted

Lifetime subscriber

#3379418 31-May-2025 14:15

OP isn’t doing 180 sqm with 10kw. They have an existing 9kw so will have 19kW of total capacity.

10kW for 5 rooms is likely about right, depending on the size of the rooms.

tweake

2647 posts

Uber Geek
+1 received by user: 1139

#3379421 31-May-2025 14:31

sorry i thought he was replacing the 9kw with the new multi system.

Geekzone support

Support Geekzone with one-off or recurring donations Donate via PressPatron.

benz1

51 posts

Master Geek

#3379513 31-May-2025 20:53

timmmay:

I can't comment on prices, except to say it's likely a lot less than a ducted system with per-room temperature controls. I will ask though, do any of the rooms such as north facing rooms ever need cooling while the others need heating? In that case you might two outdoor units, one feeding north facing rooms, one feeding south facing.

Good point but no, the whole house is either hot or cold so shouldn't be a problem. Had never really considered this possibility, but thinking about it logically, I guess a single outdoor multiroom unit cannot provide both hot and cold at the same time.

benz1

51 posts

Master Geek

#3379514 31-May-2025 21:05

tweake:

thats not really true, a bit of salesmanship there i suspect. they do run at the same time, in fact its better they do. 10kw for a 180sqm in auckland sounds way to small, but it does depend on the house. i highly recommend running your house specs through a heating calc.

also, unless your outdoor space is limited, i recommend multiple outdoor units. as mentioned hot side of the house (or top floor) may need cooling while cold side needs heating. plus multi head units tend to run less efficient especially when only a few heads are running (the less that run at once the worse it gets and this is probably why they are under sizing the outdoor unit so much.). then there is redundancy, if single out door unit fails then you loose everything.

i would look at having an outdoor unit per floor, especially as a lot of people prefer bedrooms to be colder than living room.

Valid points but as Handle9 pointed out, there is a standalone 9kW unit in the living area as well so a total of 19kW. So at least no single point of failure. (Actually for 21 years, the previous 9kW unit is the only heat/cooling we've had, plus a couple of electric heaters around the house when it got really cold.)

I would say there would be a max of three of the indoor multiroom units on at any one time, plus the standalone, but I take on board what you say about efficiency. Can the individual bedrooms not be set at a lower temperature than the downstairs units? A second outdoor multiroom unit is probably cost prohibitive at the moment although I guess a second one could be added later if it becomes a problem. Just trying to keep the whole house warm to meet my new UK wife's expectations!

timmmay

20859 posts

Uber Geek
+1 received by user: 5350

Trusted

Lifetime subscriber

#3379515 31-May-2025 21:06

Each indoor unit should have it's own setpoint.

Handle9

11927 posts

Uber Geek
+1 received by user: 9683

Trusted

Lifetime subscriber

#3379517 31-May-2025 21:53

On a multi head each unit has its own setpoint and will control to that setpoint.

A multi head does have a few limitations. The first is as mentioned you are limited to 10kw of overall capacity. The second, as also mentioned is all the units are limited to one mode, either heating or cooling. If one unit is calling for heating and one is calling for cooling one of the units is SOL.

Neither of those tend to be particularly significant if the unit is sized correctly and you are willing to use windows to provide free cooling. The more significant problem can be turndown. Because the outdoor unit is relatively large compared to each individual indoor unit you really need to have 2-3 indoor units running to get a reasonable load to run the outdoor unit in the shoulder season.

The other significant issue you have is if the outdoor unit craps the bed you have no heating or cooling for all those rooms and in 10-15 years time you need to replace the lot instead of one by one

Providing you do your homework a multi head can work really well and be a nice solution. You just need to understand and accept the compromises.

tweake

2647 posts

Uber Geek
+1 received by user: 1139

#3379629 1-Jun-2025 10:53

benz1:

I would say there would be a max of three of the indoor multiroom units on at any one time, plus the standalone, but I take on board what you say about efficiency. Can the individual bedrooms not be set at a lower temperature than the downstairs units?

each has its own set point. however its more of an efficiency problem. with bed rooms set cooler it only runs to heat the other rooms. like wise in summer where your running just the cooling on the bed rooms to get them down to temp.

multi head units are good when you have multiple heads in one big room (or two well connected rooms) and they run like a single unit. having a lot of small indoor units, each doing their own thing in their own space, is the least efficient setup. the common trick with multi's is to undersize the outdoor unit to reduce its inefficiencies when running only one or two heads. however that obviously can cause lack of heating/cooling on peak days. you would need to remember to for eg keep the kitchen/dining room unit turned off so the bed rooms can be kept heated on those very cold days.

also keep in mind, IF a heat pump system is sized correctly, its not enough to fully heat the house on the coldest day. i think auckland is sized to 4c, so those -2c mornings the heat pump won't keep up (put some clothes on). thats also assuming that its running all the time. heating a house up from cold is harder again. i mention that because you will need to keep both diner and kitchen off to maintain the heat in the bed rooms on a 4c day (not to heat it up). so you will need to work out how to run the system.

the other thing to double check is the sizing of the bed rooms units. many brands don't have small enough units for nz small bed rooms, so the bed room ones often are just the smallest that brand happens to have. i have this exact problem (same size as what you have quoted) and the units don't run properly unless its on a really cold day.

Lenovo

Shop now for Lenovo laptops and other devices (affiliate link).

bfginger

1330 posts

Uber Geek
+1 received by user: 191

#3379907 2-Jun-2025 14:58

The AP20 minisplit from Mitsubishi Electric can go down to 0.5/0.6kW heating and cooling. In general minisplits can't ramp down below 0.9kW.

tweake

2647 posts

Uber Geek
+1 received by user: 1139

#3379969 2-Jun-2025 15:42

bfginger:

The AP20 minisplit from Mitsubishi Electric can go down to 0.5/0.6kW heating and cooling. In general minisplits can't ramp down below 0.9kW.

i think thats new for mitsi nz. however i understand they do make a smaller model overseas.

benz1

51 posts

Master Geek

#3380004 2-Jun-2025 22:22

tweake:

bfginger:

The AP20 minisplit from Mitsubishi Electric can go down to 0.5/0.6kW heating and cooling. In general minisplits can't ramp down below 0.9kW.

i think thats new for mitsi nz. however i understand they do make a smaller model overseas.

Thanks both for this. Apparently both the AP20 and AP15 are available in NZ according to the company doing the install.

In the end I fed the room sizes into ChatGPT and it produced a very comprehensive report showing the recommended capacities for each room, as well as suggested models. Obviously it made some assumptions and is subject to the on-site inspection but it recommended a Mitsubishi Electric AP35 for the kitchen/diner, an AP25 for the master bedroom and AP15's for the other 2 bedrooms and study, as well as the 5F100 outdoor unit which is what was already specified. This will save me around $2,000 off the original quote for the larger units! Deposit has been paid.

Thanks all for your help and advice on this.

Scott3

4177 posts

Uber Geek
+1 received by user: 2990

Trusted

Lifetime subscriber

#3380005 2-Jun-2025 22:45

To answer the subject line of thread "Best home heating system?", it's hydronic underfloor heating, fed by a heat pump.

But it is more suitable for a new build, and if you want cooling, this likely needs to be tacked with a different solution.

--------

For OP's retrofit needs, we went through a similar exercise a year back.

Our house is ~30 years old, and not partially well designed / built thermally. Pressing need for the upgrade came from the need to cool our upstairs office and bedroom as it bakes in summer and I now spend a lot of time working from home (bedroom was previously cooled by a noisey portable AC unit). Lounge has a ~9 kW heat pump, which due to the layout of the house, means a decent amount of warmth end up upstairs, so winter heating was less pressing.

There was a wide variance of pricing, and these numbers are a year old but to give some idea:

Covering the 3x upstairs rooms from the vendor I ultimately chose:

8 kW Mitsubishi ducted system with zonal controls: $12,408
~6-7 kW (there is some error in the quote) Mitsubishi multi split outdoor unit with 3x AP25 indoor units: $9073.50
3x AP25 mini splits: $7417.50

Initially none of the quotes I had were for the 3x minsplits, Asked for that quote last minute and was glad I did.

Ultimately went the 3x mini spits for the upstairs rooms. Key decision factors:

Lower cost
Slightly higher efficiency than ducted system. (ducts run through the roofspace and are only insulated to about R0.9, so some heat/cool is lost into the roof space).
Higher efficiency than multispit (and greater peak power if we crank them all at once, but as it happens they are abundant powerful)
Greater efficiency / less short cycling with only one room on. our general use pattern is air-conditioning the office during the day and one bedroom during the night. Both ducted and multi-spit unit would be oversized for running only a single room.
Ability to run one unit on heating while other's are cooling (my spouse is strange with temperature, so this gets a lot of use).

Also got an AP25 for the one bedroom downstairs, so we have 4x matching units.

Downside of the lots this approach is that, (when combined with the existing lounge heat pump outdoor unit), we now have a total of 5 outdoor units around our house -given they layout of our house this is not an issue, but could be for others.

Also need to pay attention to wiring, installers like to save money by tapping into the back of existing power outlets for the smaller heatpump's. I paid some money, not included in the above numbers to do some extra wiring to avoid this.

On the Mitsubishi AP20 - Gave this a lot of consideration for my child room (the least roasting of the three upstairs rooms in summer) - confident the size would have been enough, but ultimately didn't go this route:

It's main selling point is the more compact indoor unit, something which was not important for our application
No built in wifi, and if you add it as an option, it errods all of the $150 - $200 cost saving vs the AP25. (I wanted wifi control at the time, but actually have found manual control is fine and never set it up).
Slightly nosier although at 18 dBA vs 21 dBA on the quietest mode, both units are extremely quiet
Slightly Less efficient EER / COP: 4.35 / 4.17 vs EER / COP: 5.00 / 4.78.
I was fairly confident the study, downstairs bedroom, and our bedroom needed the output of the AP25, and it seemed neater to have 4x matching units.

I prior poster mentioned that the AP20 does have better turn down (minimum output), and this is a valid advantage.

There was fairly massive variation in prices between suppliers. Happy air was the the one we picked.

Note our installs were timed for when we already had a key wall open, and we had to cut the jib of another wall to fit the drain pipe of two other air'cons. Repair of this was done by other trades we had on site, so not counted in the estimates above.

Should note we have underfloor heating (resistance) in our bathrooms so don't need further heating in them.

----------

OP mentioned gas.

Gas is in a sunset period in NZ.

LPG (bottled gas) is already more expensive than using a resistance heater on my power prices.

Natural gas (piped gas) based on a random retailer I picked is $2/day + 14.147 c/kWh incl GST. My power is currently 17c/ kWh, and going up to about 20c / kWh, so even ignoring that daily fee, I am much better off to use power in a COP 3 or 4 heat pump than to burn gas in a 90% efficient gas heater...

Personally I would not invest in any more gas appliances at this point, and replace the gas hot water with electric (and disconnect the gas) when the appliance reaches it's end of life.

Should note that gas fired ducted central heating, can supply a much lower volume of much hotter air than heat pumps, which can provide a less drafty experience. also can heat water hot enough to run radiators etc. Heat pumps get less efficient heating stuff really hot, so are more suited to underfloor heating or heating large volumes of air.

1 | 2 | 3 | 4