Geekzone: technology news, blogs, forums
Guest
Welcome Guest.
You haven't logged in yet. If you don't have an account you can register now.


Paul1977

5039 posts

Uber Geek


#257154 18-Sep-2019 13:57
Send private message

We have about 145m2 floor area to heat in our new Christchurch build. We have a few different ceiling heights, but they average out to 2.56m.

 

We are having low e glass and thermally broken joinery, and a minimum of R2.6 in the walls and R3.6 in the ceiling (we may upgrade to R2.8 in walls and R6 in ceiling, but haven't decided yet).

 

We have been quoted for a Mitsubishi PEAD-M125JAA which is rated at 14kW heating and 12.5 kW cooling.

 

Is this enough?

 

The Mitsubishi calculator says we require 13kW (so less than the 14kW quoted unit), but it then goes on to recommend a 20kW option?

 

 

 

 

 

 





 Home:                                                           Work:
Home Work


View this topic in a long page with up to 500 replies per page Create new topic
 1 | 2 | 3
timmmay
20574 posts

Uber Geek

Trusted
Lifetime subscriber

  #2319769 18-Sep-2019 14:00
Send private message

I have an old house, but fairly well insulated ceiling, walls, floor, and double glazing. We have two high wall heat pumps, one 10KW heat and the other 7KW heat. I probably wouldn't go much lower than that. Ducted is meant to be a bit less efficient, but probably much better distributed and more comfortable.

 

If your house is fairly new and well insulated, holds the heat well, and you leave the heating on most of the time I guess 13KW might be enough. If you use it only when it gets cold maybe you need larger.




mattwnz
20141 posts

Uber Geek


  #2319785 18-Sep-2019 14:16
Send private message

You should contact Mitsubishi technical  directly, as they should be able to work it out better for you than the rough calculators on the website. I have found installers can vary  significantly in what they recommend.


evnafets
537 posts

Ultimate Geek

Lifetime subscriber

  #2319787 18-Sep-2019 14:21
Send private message

You have to size the unit for both heating and cooling right?

 

Your unit is 14kW heating and 12.5 kW cooling.

 

So a requirement of 13kW would exceed the unit output if you are talking about cooling.  Hence why the calculator presumably recommend the "next one up"

 

 




wellygary
8312 posts

Uber Geek


  #2319792 18-Sep-2019 14:27
Send private message

Paul1977:

 

 (we may upgrade to R2.8 in walls and R6 in ceiling, but haven't decided yet).

 

The Mitsubishi calculator says we require 13kW (so less than the 14kW quoted unit), but it then goes on to recommend a 20kW option?

 

 

1. Do the insulation upgrade, it will save you $$$ in the long run, and you will never get a chance to do the walls..

 

2. the reason it recommends a bigger unit is that it is more efficient to run a larger unit at lower capacity output, rather than a smaller unit at 100% most of the time...

 

it also means that the unit has enough output to heat the room and then switch off to allow for defrosting ( esp on cooler nights), the last thing you want is a smaller unit struggling to heat the place, and then having to turn off to defrost regularly -

 

 

 

 


jonathan18
7413 posts

Uber Geek

ID Verified
Trusted

  #2319807 18-Sep-2019 14:35
Send private message

wellygary:

 

it also means that the unit has enough output to heat the room and then switch off to allow for defrosting ( esp on cooler nights), the last thing you want is a smaller unit struggling to heat the place, and then having to turn off to defrost regularly -

 

 

So true. Our ducted system is, I reckon, under-spec'd for the house; it's farcical that in the depths of winter we end up having to put the gas heater on to compensate for the inadequate heating (and periods of no heating due to frequent defrosting) from the heat pump.

 

I understand there are negative consequences resulting from going too large as well, but certainly don't risk under-specing it.

 

Another thing is, in our case, the warmth of the air from the ducted system is significantly reduced is when the outside temperature is really low; I know this may vary by model and age, but it's something to be mindful of.


Paul1977

5039 posts

Uber Geek


  #2319817 18-Sep-2019 14:49
Send private message

jonathan18:

 

wellygary:

 

it also means that the unit has enough output to heat the room and then switch off to allow for defrosting ( esp on cooler nights), the last thing you want is a smaller unit struggling to heat the place, and then having to turn off to defrost regularly -

 

 

So true. Our ducted system is, I reckon, under-spec'd for the house; it's farcical that in the depths of winter we end up having to put the gas heater on to compensate for the inadequate heating (and periods of no heating due to frequent defrosting) from the heat pump.

 

I understand there are negative consequences resulting from going too large as well, but certainly don't risk under-specing it.

 

Another thing is, in our case, the warmth of the air from the ducted system is significantly reduced is when the outside temperature is really low; I know this may vary by model and age, but it's something to be mindful of.

 

 

Can I ask what your unit is rated at, and what size your house is?

 

What are the downsides of going too large?


timmmay
20574 posts

Uber Geek

Trusted
Lifetime subscriber

  #2319829 18-Sep-2019 15:04
Send private message

I think if it's too large and the house is warm the minimum power means the heat pump turns on then off, whereas a heat pump with a lower minimum would operate continuously. I find a continuous heat / noise better than on and off.

 

We have a 10kw high wall heat pump that warms a room / hallway that's maybe 20 - 25 square meters. It turns on and off a lot.


 
 
 

Cloud spending continues to surge globally, but most organisations haven’t made the changes necessary to maximise the value and cost-efficiency benefits of their cloud investments. Download the whitepaper From Overspend to Advantage now.
jonathan18
7413 posts

Uber Geek

ID Verified
Trusted

  #2319832 18-Sep-2019 15:05
Send private message

According to this post, it's 15kW heating / 12.5 kW cooling (which isn't needed much in PN!), for a 160m house with a mix of 2.4 and 3m stud.

 

But ours is a 1920s villa with no wall insulation, so it's not an adequate comparison to a modern build, especially if you go for thicker insulation (which I would certainly do in both walls and ceiling if I get the opportunity to build); over-spec'ing your insulation would also surely have a beneficial impact in reducing the workload of the heatpump.

 

(My whole saga with our heat pump install - still not sorted to this day - is in this thread).

 

As for over-sized heat pumps, I am no expert so hopefully others on GZ who are can respond; this is the kind of thing I've been told of, whether or not all this information is accurate: http://www.southshorehvac.ca/why-bigger-isnt-better-with-heat-pump-sizes/

 

 


timmmay
20574 posts

Uber Geek

Trusted
Lifetime subscriber

  #2319838 18-Sep-2019 15:13
Send private message

We used the air conditioning way more last summer than the five summers before it.


wellygary
8312 posts

Uber Geek


  #2319840 18-Sep-2019 15:16
Send private message

jonathan18:

 

http://www.southshorehvac.ca/why-bigger-isnt-better-with-heat-pump-sizes/

 

 

"For a residential home, there is very little need for anything larger than an 18,000 BTU ductless heat pump."

 

Err. 18,000 BTU is ~5KW.....

 

I'm not sure the advice from this crowd in Nova Scotia is directly comparable to NZ...


mentalinc
3225 posts

Uber Geek

Trusted

  #2319850 18-Sep-2019 15:33
Send private message

make sure you can control multiple zones, you may want the lounge at circa 22, but that is way to hot for bedrooms...





CPU: AMD 5900x | RAM: GSKILL Trident Z Neo RGB F4-3600C16D-32GTZNC-32-GB | MB:  Asus X570-E | GFX: EVGA FTW3 Ultra RTX 3080Ti| Monitor: LG 27GL850-B 2560x1440

 

Quic: https://account.quic.nz/refer/473833 R473833EQKIBX 


jonathan18
7413 posts

Uber Geek

ID Verified
Trusted

  #2319867 18-Sep-2019 15:52
Send private message

wellygary:

 

jonathan18:

 

http://www.southshorehvac.ca/why-bigger-isnt-better-with-heat-pump-sizes/

 

 

"For a residential home, there is very little need for anything larger than an 18,000 BTU ductless heat pump."

 

Err. 18,000 BTU is ~5KW.....

 

I'm not sure the advice from this crowd in Nova Scotia is directly comparable to NZ...

 

 

Err, I never suggested the specifics on that site regarding sizing heat-pumps were relevant - it's pretty clear from the wording of my post that I was responding to the question on the issues associated with heat pumps that were significantly larger in capacity than required.


wellygary
8312 posts

Uber Geek


  #2319878 18-Sep-2019 16:06
Send private message

jonathan18:

 

wellygary:

 

jonathan18:

 

http://www.southshorehvac.ca/why-bigger-isnt-better-with-heat-pump-sizes/

 

 

"For a residential home, there is very little need for anything larger than an 18,000 BTU ductless heat pump."

 

Err. 18,000 BTU is ~5KW.....

 

I'm not sure the advice from this crowd in Nova Scotia is directly comparable to NZ...

 

 

Err, I never suggested the specifics on that site regarding sizing heat-pumps were relevant - it's pretty clear from the wording of my post that I was responding to the question on the issues associated with heat pumps that were significantly larger in capacity than required.

 

 

Yes, agree with you , but my point is if they are saying 5KW is the largest size you will need,

 

How much trust can you put in the rest of their recommendations.... ( including those on oversizing....)


Goosey
2829 posts

Uber Geek

Subscriber

  #2320691 19-Sep-2019 20:47
Send private message

Are you insulating all/every wall i.e. not just the externally facing ones, but internal walls too? Including garage?

 

Some new builds only include exterior facing walls with insulation and maybe the wall between the bathroom and bedroom and usually exclude the garage. 

 

 

 

I reccomend insulating all and every internal wall.  

 

I know someone who only needs a 7kw high wall and its generally enough to heat most of the house with only the southern bedrooms needing some back up heat sources in the winter. 

 

 


billgates
4705 posts

Uber Geek

Trusted

  #2320712 19-Sep-2019 21:26
Send private message

+1 to what @Goosey said regarding internal wall insulation. Our build has just started and we have insulated all internal walls including garage. We have picked Mitsubishi PEA-140 with Wifi card and it uses R32 refrigerant which is more efficient than R410A for 250sqm house of which 41sqm is garage and that is the 9nly area excluded from a duct run. I would strongly recommend getting the WiFi card installed and R32 variant of the ducted model




Do whatever you want to do man.

  

 1 | 2 | 3
View this topic in a long page with up to 500 replies per page Create new topic





News and reviews »

Air New Zealand Starts AI adoption with OpenAI
Posted 24-Jul-2025 16:00


eero Pro 7 Review
Posted 23-Jul-2025 12:07


BeeStation Plus Review
Posted 21-Jul-2025 14:21


eero Unveils New Wi-Fi 7 Products in New Zealand
Posted 21-Jul-2025 00:01


WiZ Introduces HDMI Sync Box and other Light Devices
Posted 20-Jul-2025 17:32


RedShield Enhances DDoS and Bot Attack Protection
Posted 20-Jul-2025 17:26


Seagate Ships 30TB Drives
Posted 17-Jul-2025 11:24


Oclean AirPump A10 Water Flosser Review
Posted 13-Jul-2025 11:05


Samsung Galaxy Z Fold7: Raising the Bar for Smartphones
Posted 10-Jul-2025 02:01


Samsung Galaxy Z Flip7 Brings New Edge-To-Edge FlexWindow
Posted 10-Jul-2025 02:01


Epson Launches New AM-C550Z WorkForce Enterprise printer
Posted 9-Jul-2025 18:22


Samsung Releases Smart Monitor M9
Posted 9-Jul-2025 17:46


Nearly Half of Older Kiwis Still Write their Passwords on Paper
Posted 9-Jul-2025 08:42


D-Link 4G+ Cat6 Wi-Fi 6 DWR-933M Mobile Hotspot Review
Posted 1-Jul-2025 11:34


Oppo A5 Series Launches With New Levels of Durability
Posted 30-Jun-2025 10:15









Geekzone Live »

Try automatic live updates from Geekzone directly in your browser, without refreshing the page, with Geekzone Live now.



Are you subscribed to our RSS feed? You can download the latest headlines and summaries from our stories directly to your computer or smartphone by using a feed reader.