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Newbie out of her depth – Samsung AE120RXYDEG 12kW heat pump

BAMi · 2025-03-09T10:58:59Z

Hi Long post, apologies!I had an ASHP (details below) with new tank and solar installed start November as part of the free gvt HUG scheme. Previously had oil CH but boiler was 25 yrs old and kept cutting out – I don’t have the money for a new oil boiler as on a low income, hence only option was ASHP as it was free. Previous Dec & Jan combined oil & elec bill was £165. Dec & Jan elec bill since ASHP was £350 & £400 😲 I can’t afford those kind of figures! I’m in a detached 1970s bungalow in the Lake District. Floor area 120 square metres. Pre-existing cavity wall insulation & loft insulation. Double glazing, not too old with trickle vents. Concrete floors. Extractors in bathroom, kitchen, utility. Pump is keeping house nice and warm, apart from lounge which is chilly. Bungalow is an L shape and lounge is in the L. It’s a north facing room and is the coldest room in the house. 2 new rads in there but it also has a huge 3m picture window. Setup: Installers: ASI Group (via contractor Rothwells) ASHP: Samsung AE120RXYDEG 12kw. Flow temp 47. SCOP 3.84. Sited on side of bungalow. Tank: Kodiak Joule 236L. Sited in former integral garage, which is now a wind & water tight room. Inverter: Solis hybrid. Currently can’t afford batteries, but requested hybrid for future batteries. 9 solar panels, total capacity 3.78kw on a South West facing roof. All new Stelrad K2 rads. All CH pipes are in loft, not concrete floor. Loft insulation was “to standard” but was topped up and is now 40cm thick. Water law is in action. Low (15C)=37C High (2C)=50C Current COP attached. DHW is set to 47C (was 50C but I turned it down as it was too hot), cycling to 60C on Tuesdays for legionella. TRVs are fully open, except in the room I work out in as it’s too hot (middle room in bungalow) which is set to 3 and also set to 3 in tiny en suite bathroom. No TRV on hall rad. Programmer & thermostat in hall. Set to 20C from 5am-9pm, then 15C overnight (installer recommended 18C but I can’t sleep in a hot room). I wasn’t given the heat loss calculation or design specification, but having read this forum have just requested both (no idea if I’ll get them though, had to chase & chase for MCS cert & DNO approval!) I’m with EON at 22.6p pkwh flat rate. SEG 16.5p (without a battery this was my best rate). I’m at home all the time as suffering from a brain tumour so bare that in mind. A cheaper night rate and higher day rate didn’t seem like a good option with no batteries. I’m frugal with electricity, trying to only use washing machine etc. on sunny/bright days timed to come on at noon. Don’t use much hot water so a huge tank being heated all the time seems wasteful, though I do have a mains pressure shower fed from the tank 🤷🏻♀️ QUESTIONS There seemed to be a mix up with the size of the pump. Installer wasn’t expecting a 12kw to arrive and to me it seems overkill for a 120m square bungalow? Install looks OK but what do I know?! Why are my bills so humongous?! What can I do to bring them down? Can't currently afford to add any extras to the system so need to work with what I have. I was given no instructions on the most efficient way of using the system. How does it work in summer? Do I need to alter anything in summer to stop heating coming on but still have hot water? Should the programmer with the thermostat be in the lounge as this is the coldest room? Or kept in hall as the hall rad has no TRV? Have read through some posts saying TRVs irrelevant and don't need thermostat, but don't understand why not as I don't want all rooms at max temp and need to be able to tell the heating when to step down at night. Confused.com! I have no clue re ASHPs etc. so any advice needs to be aimed at a child and not using technical jargon I don’t understand 🙏🏻

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Air Source Heat Pumps (ASHPs)

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Majordennisbloodnok

(@majordennisbloodnok)

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Joined: 4 years ago

Posts: 1728

10/03/2025 4:04 pm

Posted by: @jamespa

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...

Indeed; I would recommend you focus on what's wrong/what they actually need to change

...

Absolutely. My mention of the legal side in retrospect implies I was suggesting getting into litigation which is at this point unhelpful. Not how I intended it to come across, though; apologies.

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and SPH5000 inverter
1 x Myenergi Zappi
1 x VW ID3
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; sumus solum profundum variat"

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JamesPa

(@jamespa)

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Posts: 4634

10/03/2025 4:12 pm

Posted by: @majordennisbloodnok

↑

Posted by: @jamespa

↑

...

Indeed; I would recommend you focus on what's wrong/what they actually need to change

...

Absolutely. My mention of the legal side in retrospect implies I was suggesting getting into litigation which is at this point unhelpful. Not how I intended it to come across, though; apologies.

No need for apologies, just cautioning about getting too hung up on all of the mistakes (of which there appear to be plenty enough to make a case) and instead focus on the outcome.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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bontwoody

(@bontwoody)

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Joined: 4 years ago

Posts: 1009

10/03/2025 5:07 pm

@bami I think if the heat loss documentation matches a 8kW heat pump then you have a very good case as "not fit for purpose"

Alternatively if that is too convoluted, sell the 12kW model and purchase a 8kw or maybe even 5kw depending on what you discover. Its an easy job just to swap it out.

This post was modified 1 year ago by bontwoody

House-3 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60

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BAMi

(@bami)

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Posts: 29

Topic starter 10/03/2025 9:29 pm

@jamespa
@bontwoody

Heat loss calculations found and attached. Although of course the room areas are incorrect 🙄

From this do I assume the 8276 equates to a roughly 8kw pump?

CC15 1728895235575.room-by-room-calculations.pdf

Changing the subject, DHW came on today as per new schedule. I set it for 2 hours at 47C between 2pm-4pm, then had a bath at 5pm & the water was still too hot. So now turned it down to 45C and will see how that goes.

👍

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bontwoody

(@bontwoody)

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11/03/2025 12:18 am

@bami yes. 8kw = 8000w

I would change the areas in the heat loss calc to the correct ones and recalculate the heat loss.

It doesn’t mean that it is the correct heat loss but it will determine if they were correct to fit a 12kw heat pump or not.

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 4634

11/03/2025 9:11 am

Posted by: @bami

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Heat loss calculations found and attached. Although of course the room areas are incorrect 🙄

Was there any more detail or it that it? Its over 8kW, and by the time they make an allowance for DHW they would be able to argue for 12kW based on this. But I would lay money its a typical gross overestimate that much of the industry does. Your oil consumption and house size/construction is nowhere near consistent with 12kW, more like 6kW.

As @bontwoody says its worth plugging the correct areas in for a rough check. You may be able to make a case for them to swap it out which in the long run would be beneficial.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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BAMi

(@bami)

Eminent Member Member

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Posts: 29

Topic starter 11/03/2025 10:11 am

@jamespa
@bontwoody

I can't just input the proper floor areas on the installer calc as he missed out 2 windows and patio doors. So I used this online calculator (don't know if it's the correct one but it asks the right questions re floors, walls and window areas)
https://www.plumbnation.co.uk/heating-calculator

Using this calculator, heat requirements come out at 5460.94 watts, so do I assume from that a 6KW pump would suffice?

I'm going to ask the installers to re-do the heat loss calculation and we'll see what the outcome is.

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bontwoody

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11/03/2025 10:29 am

@bami I think a lot of people use heatpunk as a heat loss calculator. To me 6kW would sound about right but this is an area where installers regularly over size their systems often due to an over estimate of air changes per hour. I would guess that the majority of people get an oversized heat pump to a varying degree and getting any redress is incredibly difficult in the current system.

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Broadsman

(@broadsman)

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Joined: 2 years ago

Posts: 76

11/03/2025 11:50 am

To Bami and others with Samsung pumps. I notice that the controller is set to "Heat".

Is this correct, or should it be set to"Auto" for Water Law (as is mine)?

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bontwoody

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11/03/2025 12:38 pm

@broadsman I run mine on water law but with regards thermostat as a limiter on my warmest room so the controller does display HEAT.

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BAMi

(@bami)

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Posts: 29

Topic starter 11/03/2025 5:59 pm

@broadsman Not the faintest clue! When I read about how to change the water law settings it never mentioned changing the Heat to Auto, so I've just left it on Heat.

But like Bontwoody I also have a house thermostat which tells the pump what time to set back and when to come on if house temp gets too low.

I'll ask the installer tech guy if he ever gets back to me!

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JamesPa

(@jamespa)

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11/03/2025 6:13 pm

Posted by: @bami

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But like Bontwoody I also have a house thermostat which tells the pump what time to set back and when to come on if house temp gets too low

Don't lose sight of the fact that at some point to optimise your settings, I recommend to turn this to max and 24*7 operation then adjust your water law curve down. I suggested a procedure quite some posts ago. Your choice of course but lowest possible flow temperature=lowest operating cost and greatest comfort in most cases, and is definitely the place to start.

This post was modified 1 year ago 2 times by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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