Are Heat Pump Manufacturers trying to manipulate the figures? What size pump do you need? 

Nice overview. The heat loss of our house was estimated at 6.1kW. I was bit surprised when the installer recommended a 5kW Valliant heat pump. He was right and the heat pump copes even when the outside temperature dropped to -7C. It also has no problems heating a 300 litre hot water tank to 52C.

Comppletely agree! Minimum electrical input is SO important to reduce cycling. A heatpump that is rated to deliver 6KW at -3 will struggle to deliver just 1-2kw of heat input when the weather is milder (spring, autumn). In your example, your Minimum electrical input is say 600w, but in the milder weather (10-15 degrees) you'll be getting a COP of around 5-6, so it's chucking in 3-3.6KW of heat still. If they could modulate down to just a couple of hundred watts, it would save electricity consumption and reduce cycling by trickling in just a KW or 2 of heat when that's all that is needed.

Brilliant as always. I am bang in the middle of my heat pump journey and all of this information is so useful. Thanks for sharing all your research which must have taken you ages. Jean

Simply brilliant ...'not going to waffle'....one for the Heat Geeks to note. Simple, clear and informative. Totally enlightening.

At around 11.10 think you say output meaning input a couple of times. Still understandable . Good video. Same journey we have been on.

Thanks for publishing your heat pump electrical consumption stats. This is particularly useful for me in calculating my battery size to cover not only my normal house load but also the load for my future heat pump installation.

One thing to bear in mind for modulation ratios is that whilst it may be 4:1 at a *given outside temp*, you are most likely to need the lower output at a higher outside temp when the minimum output is higher. So the effective modulation (max output in winter vs min output in late spring) is often closer to 2:1

You always say “I’m waffling” 😊 You keep waffling! We are learning plenty thank you 👍Great videos.I genuinely can’t thakyou enough as I’m about to pull the trigger on a heat pump,my biggest issue is 10mm micro bore! 😩

This has been so helpful for my particular situation, I have just bought a 3 bed detached 112 sqm and want to get an installation from Octopus which currently uses the Valliant Aerotherm . I am going to do a loft conversion and possibly a single storey kitchen extension so adding 70 sqm . From your video I am taking the assumption that installing a 7kw now would be able to handle the addition of say 4 room radiators and a bathroom one in the future so I could install now to take advantage of the £7,500 rebate and know it should be able to support future expansion.

Thanks also for this explanation as I was thinking exactly the rating was the consumption max.

I grew up and lived most my life in cold houses. It's fine to have the house get a little cooler when it's below -3 outside. So my strategy is to put a jumper on, cook a meal, and buy a smaller ASHP.

Great video, I’m slowly pealing through my onion layers of understanding. I admit I went on trust with my HP Daikin 9kw install with Octopus (which very happy with so far), so I need to go digging first details/data. My primary view of performance is via my Alpha ESS solar battery app, which shows great real time energy use in the house, so I can see real time effects of the HP spooling up and other energy use. Currently most HP energy use - when active - is between 300-800watts. Water heating overnight is biggest jump, can spike briefly at first to above 3kw then quickly settles to around 2kw for most of work. Gaps HP not working clearly larger on milder days. But generally oscillating around 800 watts when working at the moment. This means for me during day even a poor solar day my PV covers all house energy plus HP, battery fills in gaps & gets charged ready for evening heavy use (cookjng/HP). Then 23:30-5:30 cheap rate window i use to top up battery (if needed) keep HP house warm so not working hard first thing next morning, charge EV if needed & any hot water heating. Good solar day (Saturday) I did all this and fed back 19kw to grid - crazy! Not even Summer yet, keeps raining too.

Totally not relevant to heat pumps, but you might be surprised that the electrical consumption of a microwave is typically about double what the rated cooking output is, and they run at 100% duty cycle.

Thanks for the info. The main thing that puts me off is noise levels particularly overnight.

Heatpumpmonitor - should be able to find minimum running input power for most units now, the better performing examples are often sat at that limit 24/7.

Well done in producing this. It would need Government intervention to specify a standard rating and specification across manufacturers.

This was the right video at the right time for me, thanks! I am getting quotes atm and have been struggling to understand why the heat pumps recommended have varied so much, from 7kw to 12. The 12kw Samsung pump that one company has recommended seems high to me given our heat loss of 6.5kw. But the company has generally been very good and thorough so i am inclined to trust. My concern is less that they've got it wrong and more that they're just being over cautious. In reality we only heat the house to 19 so am concerned about a pump that is pretty oversized and ends up cycling a lot. Plus it's a chunky beast! Anyway, I'm waffling...

Spot on with this video, oh I wish that the manufactures would ALL have a standard whereby @35° flow they show the output and cop at +7, 0, -3 and -7°C. it would make it a bit easier to pick the correct model. Also it would be useful to show the minimum output at +7°C.

Interesting to see the max inputs. I was wondering if the 3.5kW Vaillant would ever draw more than my inverter can kick out (3.3kW max) and from your 7kW numbers it seems unlikely. Of course, if something else is running at the same time it may well do it.

The reason nothing has changed and everything is still being oversized is because MCS regs say your HP must cover ALL heating requirements at -7°C to qualify for the BUS. MCS are not allowed to install a system that might require a little convector or an extra blanket on the three days a year when it is actually that cold. Even though you might have a log burner or storage heater for those coldest days - they have to ignore that. They also ignore any solar gain you might get and funnily enough the sky is usually clear and the sun shining on the very coldest days. You also have heat from the TV, cooking, pets, people, etc - all irrelevant to MCS calcs.

I have found the Mitsubishi information the best of the bunch for those who really want to go into the details; the Ecodan A2W Databook has masses of information (min/part-load/max power output at 5 deg C increments of air and water temperatures). However, yes their two-page data-sheet is a bit weak.

I'm in the US (Colorado) so my system is very different - ASHP, air handler and air ducts throughout the house. I have seen the heat pump come close to its rated maximum input power but at 10C below the design temp (-18C here). Those days were big outliers on my data. Other people in my area with similar installs added supplementary heat and/or turned down the thermostat for those days. Our house is about the same size but the temperature swings here so much, my heat pump is 14kW and probably only a little oversized.

I decided not to go with Octopus as they would only put in Daikin ASHP's. Anecdotally it looked like the minimum daikin running elec consumption was higher than the Vaillants plus integration/API's seems better with Vaillant. Any thoughts/comments ASHP guru's?

Thanks, I’d also been looking at the first three models and only the Vaillant seems to quote real figures across different temps and so 7kW would be the nominal with a bit extra unlike the others where the figures are just fingers in the air…

I faced with the same difficulties when I looked at pumps suitable for my house I do confirm that it is very hard to find useful info, when you want to know more than the basic info (in Italy the law is to inform about power output and COP at 7°C OT and 35°C delivery flow, and also at 45°C flow. Typically you must be an installation company to have access at more data (at least on the italian website, but I cannot access any other). More data are available to everybody from LG for their R32 ThermaV Monobloc S versions, even if I feel that some info is possibly not accurate. I compared the three units that are rated 12, 14 and 16 W (at -15°C, while operation down to -25 is possible with reduced output), which are certainly the same machine assembly with just a different tuning: on paper they are rated for modulation down to 11 to 13% (and the circulating pump down to 10%), but I could not find much info of what the COP will be at those low power output. There is however a table suggesting data for a "typical" system at various external temperatures: interestingly, as the power output is reduced, the COP gets better. Among the three units (of the same construction) the lower power are slightly more efficient. On the user manual of the same units you have many different control options: e.g. you can select the deltaT, or even the circulation pump speed, if I correctly remember, which should allow you force the heat pump to operate at different power outputs, at a given temperature (but this is my theoretical understanding).

Can I ask where you get the usage info around 12.00 into this. We also have vaillant Arotherm.

Where can I find the 4 to 1 modulation data for Vaillant ASHPs you mention in the video.... Have I wrongly assumed that Vaillant low modulation was simply a ratio of the minimum & maximum l/h flow rates which is closer to 2 to 1.

Hello. Isn’t the 7 kW arotherm plus rated ussually at w35? At A-5/W35, it generates more like 8,2kW. Why do you compare -5/W55 with others at W35 and 45?

Welcome to the world of the "Ratings Game". It has always been the case that AC & Heat Pump manufacturers rate & produce performance data to show their products in the best possible light. Car makers do exactly the same with prescribed fuel consumption test procedures under lab conditions, which as we all know, bares no resemblance to real world results because replicating real world conditions for different types of drivers & ways of driving is impossible to achieve. The same is true for Heat Pumps. Interestingly, Air to Air split heat pumps have long since shown minimum & maximum heat/cool capacities & power input data for different models (at least the manufacturers that I was involved with did). However, the temperatures (inside & outside) that were used to generate this data could vary widely so once again there is plenty of opportunity to "manipulate the numbers". And, as you have found, the same is true for ATW products. In an effort to make comparisons between different makes more easy industry bodies require individual heat pump models to be tested & rated at specific conditions. This can be done in-house at the manufacturers factories providing their facilities meet the governing bodies test, measuring equipment & procedural standards. Governing bodies will visit & witness the manufacturers testing facilities to ensure their compliance. Governing bodies will also do spot checks by testing randomly selected / purchased heat pumps & test them in its own lab facilities. In the UK the most well known of these test houses is BSRIA who I had dealings with when I worked for two different heat pump manufacturers. This data is also used for the energy labels attached to each product. That said it is still not easy to do meaningful comparisons between manufacturers when there are so many installation variables that can affect the overall system performance e.g. the type of emitters used, the pipe sizes, lengths of pipe & pressure losses, pump sizes, buffer tanks or not etc etc. To combat this most ATW manufacturers should publish a "short form" of capacity & power input product rating based rads or UFH & different flow temps. This is typically shown in their sales catalogues & should be the same format for each make in an attempt to level the playing field. Whilst not totally accurate it can be used as as a quick way of comparing different makes. However, for all the reasons stated above accurate comparisons between makes are almost impossible due to the many variables involved. Last but not least, oversizing of heat pumps is still fairly common & is a hangover from the days of boilers when sizing was, how should I say, more of a guesstimate than a science. It's far better to slightly undersize a heat pump that to oversize it. Now I'm waffling so I'll stop!!!!!

I strongly recommend Toshiba Estia for you. For 8kW pump you get following modulations for 7 deg and above: 1.01, 1.17, 1.28, 1.45. Much better than I've see.

Not sure if you can help , I am having two pumps and installer is quoting for two Mitsubishi ecodans labelled 11kw . From what I am reading Vaillants would be preferable all round , agree or disagree?

Interesting video, I am assuming that as that energy demand drops you will be along the heat curve and therefore the flow temp will be lower, that again increases COP and doesn't help the low modulation. I did have the chance to get a 5kw arotherm, but went for the 7kw as my heat loss is 7.6kw at -3. Ouu by the way second hand pumps can be had , lol. I have my 7kw, as its DIY, I am putting in 35mm primary and twin mag and y strainers, because I can.

To be fair, the calculations and the MCS requirements are complex. If I was an electrician or a plumber I'd just prefer to use a bunch of rules of thumb and avoid the paperwork. I'm pretty sure that a 5kW heat pump will be fine for my house (based on detailed calculations and closely monitoring my current gas system) but I suspect that I'll be quoted 7kW and above when the plumbers come round this week. There's no incentive for a plumber to quote a smaller system - less money overall and a greater chance of a customer call-back when they're too cold.

Still learning about heat pumps so sorry if I get things wrong , I did hear that there’s a new refrigerated system that is coming in by Jan 2025 I think it’s part of the in coming law or requirements within the industry, heard about this the other day , did I get it wrong or should I cut down on the whiskey.

We are in the process of getting a heat pump from Octopus our heat loss in the house is 6.5kw. Octopus initially specified the 9kw Daikin however the 9kw HP has a minimum electrical input of 950w where as the 8kw heat pumps minimum electrical input is 325w a massive difference that ultimately would have cost me on my bills. Discussed with Octopus and they were happy to change the HP to the 8kw. Apparently the 4,6 and 8kw HP are all exactly the same the first two are limited by software only so it makes sense that they all take the same amount of electricity to run them at the lower output end. Again the 9,11,13 and 16kw units are all the same unit thus the reason why there is such a difference in minimum electrical input between 8 and 9kw units.

Maybe the 3.5 kw pump would have been the most efficient would be undersized at 70% as some dedicated software recommends. Nothing is lost and I recommend trying to find the temperature at which the pump stops cycling and heating to different temperatures during the day. It is now oversized only for 24/24 use but not for 12/24 or even less hours of operation.

The Vaillant max power input numbers do seem to be available on the "Installation and maintenance instructions" PDF on page 46 not sure what the external design temp is probably -2 or -3 is my guess I contacted my DNO recently and even they thought 7kW was peak electrical power input so it's not just consumers

So much cycling. Definitely got an oversized heat pump.

They manufactures need to do a lot better with modulation, problem is we need more awareness. I’ll probably keep my 10:1 boiler until they do better.