Newark HG DHW Cylinder ROI

Hi Everyone,

This looks like a great community… This is my first post and I really hope that someone can help with a few questions regarding a new Air Source Heat Pump installation I am planning to install in the not too distant future.

I am particularly interested in optimizing’s my DHW setup as it would appear that this if often the achilles heel of most ASHP setups when it comes to maximizing the systems performance.

I live in Denmark and have recently renovated my 180m2 house with underfloor heating using 150mm pipe spacing throughout the house. (No radiators) In addition to installing the required (Danish building regs) 400mm of floor insulation and 300-400mm of loft insulation.

Currently I can run my old gas boiler at 30-35C with outdoor temperatures at -12C without any issues.

According to my calculations using the MCS Heat Loss Excel Spreadsheet I have a total heat loss of 5,7kw having adjusted the MCS spreadsheet so that the Outside Design Temperature (ODT) and the Degree Days (DD) match my location here in Denmark.

On top of this we have 4 people in our household and 2 bathrooms both with high flow shower heads installed.

What I have discovered so far
After a lot of research and calculations I have come to the conclusions that I want to purchase a “Vaillant AroTherm Plus 7Kw” which I believe will be sufficient to meet our heating requirements.

But what I am really curious about is which Unvented Indirect DHW Cylinder I should go for?

I read a great article looking into various DHW Cylinders performance written by @Zarch which I would really encourage everyone to read. It’s a great comparison of how various types of cylinder effect your SCOP, well worth the read.

What I am really interested in is how say a Newark Heat Geek Cylinder with a 6m2 coil surface area compares to say a Vaillant uniStor 300L cylinder when it comes to return of investment?

Looking at current prices for a Vaillant uniStor 300L Cylinder (Currently £1100) compared to a Newark Heat Geek 300L Cylinder (Quoted Price: £2500) I am a little unsure that there is a viable argument for purchasing the Newark Cylinder.

I noticed that @Zarch had the Newark Heat Geek 250L cylinder priced at £1,869 (retail price*). I would be very interested in knowing if this is a stainless steel cylinder with the outer case and what insulation it comes with as standard???

With a £1400 price increase compared to a standard ASHP DHW Cylinder I am really not sure that it will ever provide a return on the initial investment based on the savings it should otherwise give?

P.S. I would be happy to share my quote from Newark with anyone who is interested unfortunately as a new user I am not able to upload files to the community.


I am having a Newark cylinder installed today.
It’s not one of the “Heat Geek” models, but it was specified by a Heat Geek installer.
4m2 coil and 87.5mm insulation. 1.03 kWh/24h standing heat loss.
Give me a couple of weeks and I will be able to let you know how it compares to our current Kingspan cylinder with a 0.77m2 coil and much thinner insulation. 1.89 kWh/24h

It’s obviously going to transfer heat better with the larger coil but, perhaps naively, I expect to see savings from the better insulation where it should hopefully require less energy to re-heat the water.

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Diminishing returns for smaller heat pumps.

6m2 coil @12kW or 3m2 coil @6kW is much the same thing. If you can tolerate the “eco” runtimes and can wait until the cylinder is mostly discharged before refusing it even better performance will result.

Look at the 1.5m2 coil on @glyn.hudson installation for good performance even with small coil on an older heat pump - mostly by waiting for the cylinder to be near empty before recharging.

I would be looking at drain water heat recovery if you materially want to improve hot water efficiency for showers.


@LeiChat Thank you very much for sharing your experience! I am sure it will be a big improvement if you are using a heat pump. Most Heat Pump Cylinders have at least 3m2 of coil today in standard cylinders. For example the Vaillant uniStor has a 3,2m2 28mm coil. which would also be a lot better than your 0,77m2 on the Kingspan cylinder.

What I am really interested in knowing however is how long will it take for me to get my money back especially on a cylinder that I have been quoted £2500 for compared to say a Vaillant uniStor 300L cylinder.

Where do I find @glyn.hudson data?

Obviously there is a big benefit to using all the water you have paid to heat. That makes a lot of sense! The question here is how much does a 6m2 coil running at a much lower dT and flow rate effect the overall economy in the long run.
I think what Adam at Heat Geek is doing makes a lot of sense but I am also interested in the economic aspects should I choose to go this route.

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It’s on Here’s a direct link:

DHW SCOP for the past week is 3.9

Here’s a bit more info about my system;


This is another option:

Preheating the water will reduce heat pump COP slightly but you’re recovering heat for free.

Let’s say COP 4.5 for 45 litres means 20 litres of electricity to give 90 litres of hot water id the best you can get.

If you get 22.5 litres of hot water for free (this is typical for wastewater heat recovery - metered data) and then a (slightly reduced because of preheat) COP 4 for the other 67.5 litres that means 15 litres of electricity used.

15 litres of electricity into 90 litres of hot water gives COP 6.

£ for £ that beats any cylinder upgrade for improving heat pump COP.

£ for £ extra PV probably also beats it.

For cylinder payback:

  • a 3m2 coil in a 300L cylinder with a 5 or 7 kW Arotherm will be at least sCOP3

  • £0.30/kWh means £0.10/kWh of heat

  • 1 m3 from 10C to 40C is 35 kWh or £3.50

  • Say a 6m2 coil in a 300L cylinder with a 5 or 7 kW Arotherm will be at least sCOP4.5

  • £0.30/kWh means £0.067/kWh of heat

  • 1 m3 from 10C to 40C is 35 kWh or £2.35

Payback after 1000 m3 of mixed water.
1000 m3 is 1,000,000 litres, or 100,000 minutes at 10 litres/minute, or 1,666 hours in the shower

Plausible over cylidner lifetime

If the standard setup gives sCOP4 then you’re looking at payback after 3000 m3 or 5000 hours in the shower. More marginal but plausibel within lifetime for a heavily used setup.

Quick sanity check: 365 days per year; 3650 days in 10 years; 7300 days in 20 years. Say cylidner lasts 7300 days. 5000 hours is quite heavy usage but not implausible with a family setup.

3,000,000 litres over 7300 days is 410 litres a day though; so you would be emptying and reheating that big 300 litre cylinder twice a day to hit this kind of figure. Is that what you do?

I suspect what you’ll find is that the 300L / 3m3 cylinder on a small Arotherm in the ECO mode where the comrpessor / evaporator are also most efficient gives sCOP4.5 anyway. I don’t think anybody has measured one yet though.

I’d spend the £1000 on wastewater heat recovery myself.


Okay… Funny I have actuallly watched some of your YouTube video before… I didn’t put 2 and 2 together… Your profile image on OpenEnergyMonitor is slightly different. :wink:

Thank for the great tips…

What do you think of the Samsung 8kW HT Quiet R32? Everyone is talking about Vaillant on YouTube as a high end option so I am a little interested to hear why you have gone with the Samsung?
One aspect that is SUPER important for me is the noise levels due to certain Danish requirements and the fact that we need to install ours on our boundary line.

I was planning on going with a Vaillant Arotherm Plus 7kw, but having had a look at some of Samsungs new offerings I can see that the HTQ might be an option. I would love to hear your thoughts.

I have a 7m insulated 40mm Pex pipe running from the boundary to the house underground (Uponor EcoFlex) and plan to then split break off to a 35mm Copper pipe and then down to 28mm as I have a 5m run to my indoor Underfloor Heating Manifolds.

I think I have also decided to drop the Newark HG cylinder as it doesn’t make a lot of sense thanks to @markocoheat input and explanation. However I would really like to hear which 300l cylinder people would recommend. I have previously looked at Vaillant’s UniStor 300L as well as the Gledhill Stainless Lite Plus Heat Pump

Love all the input you guys have provided the community… Keep up the great work! :slight_smile:

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I’ve got a 5kW Samsung Gen 6, which is a totally different product line to the HT/q. See highlighted

My 5kW Gen 6 is pretty quite, but the Vaillants are even quieter. From what I’ve heard, the new Gen 7 HTQ are quiet, but the performance does not seem to be a good as the Gen6. They seem to have optimised for higher temperature instead of efficiency, the 8kW HT Quiet model shares the same compressor as the 14kW model, so low end modulation is poor. Here’s an example of a 8kW HTQ on HeatPumpMonitor.

Samsung have just launched a R290 range which looks very interesting. I would choose R290 over the HTQ R32.

I’m very happy with my Gen 6 5kW Samsung unit, I choose it became its relative small and light, I wall mounted mine at height. It’s also got a good documented modbus protocol and significantly cheaper than Vaillant. As you can see from my system on it’s getting excellent efficiency. However, the controller and the control algorithms are not as advanced as Vaillant, it requires more tweaking to get it running at optimal efficiency.

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@glyn.hudson Is this the model you are referring too?

Looking at the installation manual the Vaillant still appears to be quitter than the new Samsung EHS… Perhaps better just to stick with my original plan.

I have a deadline as I am planning on coming over to the UK to visit family and then taking a heat pump back to Denmark in the middle of Feb. due to the stupid Scandinavian prices and a great excuse to visit family and friends.

Just to give you an idea a Vaillant Arotherm Plus 7kw costs £6500 in Denmark and a unistor 300L is £2200… :money_mouth_face:

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The EHS unit lauched running R32.

That either tells you about how little Samsung invested in R&D or it tells you that they had more problems with R290 than they would have liked. (i.e. they rushed out an “temporary” unit at the last moment until they could finish the R&D for R290)

Wouldn’t want to touch either the R32 unit or the R290 unit as a one-off import for this reason. (unless DIRT cheap) The R32 unit is an orphan and the R290 unit is suspect given the delayed launch. Wait for A N Other to be a guinea pig.

It’s also a high temperature optimised unit (not what you need from what I see) with quite a high minimum output (unlike Vaillant they don’t publish full datasheets; but have indicated 4 kW in some correspondence elsewhere).

I’m surprised at the price discrepancies between the UK and Denmark on the Vaillants. Is it a case of a small country cartel in operation; import taxes; or are there just no “wholesalers” with piricing accessible to the public in Denmark?

Very interesting thread here… Lots to read! Not sure if it’s been mentioned by anyone, but I have been happy enough with 3sqm coils for say 5kw of heat, and tend to like it occupying the lower half of the cylinder. Otherwise you cannot benefit from heating the cold bottom. With a tall coils, there could be heat taken from the top. I guess it will sort itself out, but not ideal nonetheless

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@markocoheat Thanks for the background on the Samsung. I will stay well away! As previously stated I was planning to install a Vaillant AroTherm Plus 7kw anyway.

With regards to the pricing… we have the same VAT etc as in the U.K. but I think it’s just the way things are generally in Scandinavia. People have gotten use to paying high prices and I guess it’s a small market so it makes it more difficult to cover higher costs.

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Yes that’s the new R290 one.

I agree with @markocoheat about the R32 HTQ, the performance of the system on heatpumpmonitor example, doest not seems to be that great, R32 is not the best choice for high temperature.

My positive experiences is with the Samsung R32 Gen 6 unit which is a totally different unit, there are plenty of high performing examples of Gen 6 units on

The new R290 units look interesting, but would want it to know more about then and see some real work monitoring data before committing,

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On the 31st we had our existing 150L Kingspan cylinder replaced with a Newark 170L cylinder.

Prior to the 31st our average DHW cycle COP was 2.7 (34 days)
Our new average is 3.8 (only 4 days so far as solar diverter has topped it up on the other 3).

The old cylinder had 50mm insulation and a 0.767m2 coil surface area. Standing heat loss rated at 1.89 kWh/24h

Newark has 87.5mm insulation, a 4m2 coil surface area and standing heat loss of 1.03 kWh/24h.

Would obviously be better to compare a cylinder of the same capacity.

While the better insulation helps reduce how often we would need to (re)heat the water, some might argue that could result in lower COP because the ASHP is more efficient when heating water from a lower temperature. :rofl::thinking:

My hope for the upgrade is that we use less energy overall annually and the power consumption is lower, leaving more available for other household consumption, when it’s all running off the storage battery.

We do not have children though, so hot water consumption is probably well below average. Hopefully someone in the OEM community will be able to share a comparison for a larger cylinder.

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So amalgamating the info we have.

Some people with smaller coils are getting 3.8 COP for DHW. Adam is getting 4.06.

The cylinder costs £1100 more.

Electricity is £0.30 kWh.

Average daily kWh for DHW seems to be about 8 kWh.

So that would be an electricity saving of 0.135 kWh per day.

That saves £0.04 per day.

So payback is 75 years? Longer if smart tariffs are taken advantage of. Can that calculation be right?


@JM97 Yaaa… Expensive don’t you think! :thinking:

One thing that isn’t taken into account here is the likelihood that electricity prices will increase as we switch to use electricity more and more in the coming years…

But… The ROI still doesn’t make sense!

There is also reheat time.

You can bang in 12 kW with the 6m2 coil and get decent COP. You can’t do that with a small coil.