Correct Heat Pump size for rental

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quebec

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#320004 24-Jun-2025 20:19

Got two quotes. First company 3 Yes Heat Pumps says space requires Mitsubishi AP50 with wi-fi $2854. 1 year workmanship warranty. Second company Design Air says as per tenancy website calculator it requires 4.9kw heat so Mitsubishi AP42 is enough, $2708 non Wi-Fi, $2807 Wi-Fi. Other option from them is Panasonic CS/CU-Z50AKR 6kw heating with Wi-Fi $2604. Design Air offers 5 years workmanship warranty. Does workmanship warranty matters? 3 YES says it doesn’t as workmanship issues if any happen within first few months. Has anyone dealt with either of these two?

Lounge is 7.3x5.3 =38.69 sqm. I’ve heard Mitsubishi Electric are better than Panasonic so leaning towards that but what size? I understand that for healthy homes compliance I can install what tenancy website calculate says but I also want it to be the right size.

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#3386872 24-Jun-2025 21:40

Personally, I would go for the larger one, there is only a few dollars in it.

As for brand I cant help you.

In my last house I had a Toshiba and it was very lackluster, we replaced it with Mitsubish heavy Electric ( different company to Mitsubishi ) and it was a lot better.

In out current house we have a Mitsubishi and it is very good.

Our MHE heatpump had wifi, it was a module that went deep inside, there was no way to change the wifi SSID without pulling it apart, so when the tenant moves, it may be a hassle. The one you are quoted may be better.

John

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#3386874 24-Jun-2025 21:58

I've got a Panasonic Z50XKR for my Kitchen/Dining/Lounge area which is 9.5*4, so nearly identical by volume to yours.

I knew it was slightly undersized but have other Panasonic heat pumps in every other upstairs room. If I didn't always have the other units on, I'd be regretting not going larger as it does struggle a little on the hottest summer days when we have heaps of people over.

The unit above replaced a smaller 3.5kw Mitsubishi that we relocated to another bedroom downstairs after we pulled a wall down between lounge and dining. The Mitsubishi is much quieter both inside and out, even compared to another 3.5kw Panasonic.

The Panasonic has the wifi module, and 1/2 degree increments which I like.

fe31nz

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#3386884 24-Jun-2025 22:58

We have a Panasonic CS-Z21RKR in our kitchen (about 7.2 kW heating from memory). In the bedrooms and dining room we have small Mitsubishi Electric MSZ-GE25VA units and in the sitting room a mid-size MSZ-GE50VA. The Mitsubishi units are all very quiet when in quiet mode, and so are good for a bedroom. But I hate how their remotes work - you have to turn the unit on before you can adjust any of the settings (heat/cool mode, fan speed, ...). With the Panasonic, you can adjust anything at any time except the Powerful mode and another mode I have never used. And the Mitsubishi units are very slow to start heating the room. You have to wait for about 10 minutes before they are putting out a good amount of heat. So you need to plan ahead and get the Mitsubishis turned on in time to use their rooms - at least 25-30 minutes before you want to use the room. The Panasonic has a very large room to heat, but if you select Powerful mode, it will be putting out some heat in less than a minute and as much heat as it is capable of in 2-3 minutes, and will heat the big kitchen much faster than the smaller Mitsubishis heat their rooms. That is so much better that I would recommend the Panasonic for any room where you do not need a super quiet unit. I like the Panasonic. I tolerate the Mitsubishis for their quietness.

When choosing a heat pump, make sure it is using the latest refrigerant. The CS-Z21RKR is using R32 (the latest when we got it), and is significantly more efficient than the older Mitsubishis. From memory, in the Panasonic range, the R32 units were about 4.5x on heating. and the older refrigerant models of the same size which were still on sale were only about 3.5x. The smaller Mitsubishis do about 4.0x, and if we had bought a big one of them for the kitchen at the same time it would have been only about 3.2 I think - smaller heat pumps are more efficient than bigger ones. The newer Mitsubishis of the same small size but with R32 were up to 6x. I am not sure if R32 has now been replaced with something better again.

bfginger

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#3386897 25-Jun-2025 07:13

The AP42 and AP50 are inefficient and the AP50 only ramps down to 1.4kW.

I suggest the Daikin Cora FTXM50UVMZ or Daikin Alira FTXM50WVMA or Mitsubishi Heavy Avanti Plus SRK50ZSXA. Or a Hitachi P series RAS-P50YHAB if it won't have to cool too much as this one's more efficient at heating than cooling.

"When choosing a heat pump, make sure it is using the latest refrigerant"

I don't think there are any R410A minisplits still on the market in New Zealand but it does not matter too much. R32 does perform better than R410A but in many cases the efficiency gains were leveraged to reduce material inputs more than increase performance. A good R410A unit is more efficient than the quoted Mitsubishis.

For hot water heat pumps it's different as CO2 or propane are so much better than previous generation refrigerants.

timmmay

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#3386903 25-Jun-2025 08:06

Mitsubishi or Daikin brands are likely better than Panasonic. I would go with what the healthy home standard requires. Size required depends on insulation. Too large and it will stop / start, whereas a smaller heat pump will run continuously at lower power and likely last longer.

quebec

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#3386925 25-Jun-2025 09:50

As per healthy homes calculator, it requires 4.9kw of heating capacity with an outdoor temperature of 1°C. What are heat pumps normally rated at?

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quebec

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Ultimate Geek
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#3386939 25-Jun-2025 10:49

Spoke to Mitsubishi, their units are rated at 7°C so he said I should go for AP50 is 4.9kw is required at 1°C. He also said all installers should give workmanship guarantee for 5 years. If they don't any issue arises due to workmanship you can claim through CGA.

Kickinbac

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#3387091 25-Jun-2025 20:58

quebec:

Spoke to Mitsubishi, their units are rated at 7°C so he said I should go for AP50 is 4.9kw is required at 1°C. He also said all installers should give workmanship guarantee for 5 years. If they don't any issue arises due to workmanship you can claim through CGA.

There are performance tables for each model at different outdoor temperatures. I’ve got access to them on BDT website.
The AP50 does:
5.1 kW at 0 degree C outdoor temp and 21 degree C indoor temp.

5.37 kW at 1 degree C outdoor temp and 18 degree C indoor temp.

So has the right performance for your healthy homes calculation.

Personally I would use Mitsubishi Electric over anything, Daikin second, then all the rest. Depends on what the price is as Mitsubishi are usually the most expensive.

vexxxboy

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#3387094 25-Jun-2025 22:06

when we got our heat pump they measured our lounge and said we only need a 4.kw heater , when the installer came around he asked us do we keep the doors closed in the lounge and we said they were never closed and he said the 4.5 kw would do but it would be on all the time and would ramp up the power bill and he recommended the 7.2 kw and he said he always recommends to go as large as you can because it takes under half the time to heat a room and will save you money in the long term as it doesn't need to be on as much .So we did and the extra benefit is that it heats the whole house so we dont need extra heaters. It costs us around $50- $60 a month in winter to run it.

Common sense is not as common as you think.

Handle9

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#3387102 25-Jun-2025 22:54

vexxxboy:

when we got our heat pump they measured our lounge and said we only need a 4.kw heater , when the installer came around he asked us do we keep the doors closed in the lounge and we said they were never closed and he said the 4.5 kw would do but it would be on all the time and would ramp up the power bill and he recommended the 7.2 kw and he said he always recommends to go as large as you can because it takes under half the time to heat a room and will save you money in the long term as it doesn't need to be on as much .So we did and the extra benefit is that it heats the whole house so we dont need extra heaters. It costs us around $50- $60 a month in winter to run it.

It sounds like you were dealing with someone who is fairly clueless about how to design heatpump systems but wanted to sell you a bigger machine. "Go as large as you can" is just wrong.

Oversizing, and the associated short cycling, is nearly as bad as undersizing the machine. You are shortening the life of the machine with short run times on the compressor, potentially have terrible control by over heating/cooling during minimum run time, and operate outside the design point for the unit resulting in poor efficiency.

A good installer will do calculations and select a unit very slightly oversized not make stupid blanket statements like "go as large as you can."

vexxxboy

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#3387125 26-Jun-2025 08:13

Handle9:

vexxxboy:

when we got our heat pump they measured our lounge and said we only need a 4.kw heater , when the installer came around he asked us do we keep the doors closed in the lounge and we said they were never closed and he said the 4.5 kw would do but it would be on all the time and would ramp up the power bill and he recommended the 7.2 kw and he said he always recommends to go as large as you can because it takes under half the time to heat a room and will save you money in the long term as it doesn't need to be on as much .So we did and the extra benefit is that it heats the whole house so we dont need extra heaters. It costs us around $50- $60 a month in winter to run it.

It sounds like you were dealing with someone who is fairly clueless about how to design heatpump systems but wanted to sell you a bigger machine. "Go as large as you can" is just wrong.

Oversizing, and the associated short cycling, is nearly as bad as undersizing the machine. You are shortening the life of the machine with short run times on the compressor, potentially have terrible control by over heating/cooling during minimum run time, and operate outside the design point for the unit resulting in poor efficiency.

A good installer will do calculations and select a unit very slightly oversized not make stupid blanket statements like "go as large as you can."

well it has lasted 15 years and counting and our power bill is only 50 to 60 extra a month in winter so i guess it worked out.

Common sense is not as common as you think.

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Kickinbac

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Ultimate Geek
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#3387136 26-Jun-2025 08:51

@Handle9 What constitutes over sizing? There are many variables and trade offs.

If selected for heating, its important to know the performance on the coldest days of the year for the heating capacity. This is more critical the colder your region.

99% of installers probably don't do a proper heat load calculation, which is what the healthy homes calculator is intended to solve. The healthy homes calculation usually puts the selection a size of two larger than what is normally selected (in my region) because of the coldest day requirement.

You can use a plug in electric heater to add capacity for the 5-10 coldest days of the year.

I often look at the the inverter range which might be something like 2.0kW - 10.8kW (based a Daikin Cora 7.1kW) to check where the compressor is cycling on/off. If the inverter switch off point is higher, say 4.5kW - 9.0kW, I'm looking closer at the specs and looking for a better heat pump unit.

A benefit of an oversized unit is that it runs slower so less fan noise most of the time.

I mainly do commercial and industrial HVAC systems, big stuff, and only do a handful of residential in a year, usually existing clients. So I'm lucky in that I don't have any residential sales targets or competing with the other guy down the road with his cheap price and crap unit and install. If they go somewhere cheaper I'm not bothered and they are not the customer we are after. lol - most landlords!

Sometimes we have to oversize units only because of the maximum pipe lengths. A 3.5 kW unit may have a maximum pipe length of 15-20 metres and what if we need to do 25 metres? We have to to select say a 4.6 kW unit, being the next unit available with increased maximum pipe length of 30 metres. For example, a new 4 level retirement village apartment building with the outdoor units in the ground floor carpark with a 40 metre pipe run for a 3.8 kW of heating capacity. It was not ideal as we had to use commercial heat pumps that had 50 metre pipe lengths.

quebec

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Ultimate Geek
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#3387233 26-Jun-2025 17:08

Just got invoice(bank requirement before install) which doesn't mention 5 year workmanship warranty and dedicated power supply from board which I discussed yesterday before finalizing, replied and got this answer. They are putting workmanship guarantee on invoice. What does it mean? What's the point of running power supply from switchboard if it's not on it's own MCB or am I missing something.
'We will run the power supply from the board but not from a dedicated supply as I did not look at the switchboard and do not know if there is room.'

Handle9

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#3387234 26-Jun-2025 17:13

Go and take a photo of the board and send it to the contractor. That will tell them if there is room.

Even if it doesn’t have a dedicated MCB its own feed means it won’t run the risk of overloading the wiring of the existing circuit.

quebec

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Ultimate Geek
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#3387235 26-Jun-2025 17:21

Handle9:

Go and take a photo of the board and send it to the contractor. That will tell them if there is room.

Even if it doesn’t have a dedicated MCB its own feed means it won’t run the risk of overloading the wiring of the existing circuit.

Yeah I'll get a photo. So, even if it doesn't have a dedicated MCB, on the switchboard it will connect to an existing MCB with other loads, isn't it similar to taking it from the nearest powerpoint? Or are they hoping to find a 20A one with less load or only lighting?

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