Air source heat pump electricity consumption in November

by Mars

As temperatures outside drop, our air source heat pump has had to kick into higher gear. As part of our ongoing series to share the efficiency and performance of our pump in a period property, we’ve shared our November numbers in this post.

The data for November is not 100% accurate because the electric meter counter stopped recording midway through November 27, 2020. Global Energy Systems rebooted the logging equipment remotely, so we’ve taken an average of the figures from November 27-December 1, 2020, to complete the picture.

If you’d like to see what our numbers were like last month, please refer to our October figures.

Our overall compressor consumption for November was 1,161.24 kWh which was up from October’s 1,031.50 kWh. This makes sense because the average outdoor ambient temperature dropped from 9.32C in October to 8.04 in November.

Based on our current electricity tariff of £0.165 that means we paid £191.60 to heat the entire house and hot water demand last month. The house, with the continued exception of the TV room, has remained at temperature (21C) in most areas, 24 hours a day, which we feel is reasonable.

The test, as it was last year, will be December, January and February. We have done a lot of work around the house to better insulate it, so it’ll be interesting to see if it reduces compressor consumption. Rooms do feel warmer, and stay warmer for longer.

We are still looking at new ways to improve the efficiency of our heating throughout the property. Watch this space.


Andras Meszaros 5 December 2020 - 08:49

What is the total floor area of your house?

Mars 5 December 2020 - 08:50

Thanks for the question Andras. We’re heating around 4,000 sqft.

Andras Meszaros 5 December 2020 - 09:03

I would say that is very inpresive for such large old house!

Mars 5 December 2020 - 09:06

We think it’s doing well, but we’d like improve things further.

Andras Meszaros 5 December 2020 - 08:57

Sorry forgot to ask how many sqvered meter is heated with underfloor heating and how many is with radiators? U mentioned that your flow temperature is 45 degrees. Is 45 goes through your underfloor as well or does it get rudiced ? Does your system not reduce flow temperature acording to outside ambian temperature? I have a Samsung system and it rekons it saves me 25% if i set it to weather dependent mode insted of constan temperature.

Mars 5 December 2020 - 09:06

Most of the downstairs is UFH, and upstairs is rads. Probably a 40/60 split (more rads).

No, our flow rate doesn’t change based on ambient temperature. Does your Samsung do that? If so, that’s pretty cool.

Andras Meszaros 5 December 2020 - 12:18

Yes it does. It is a great feature.
In this link if u go to 4:45 they are atchally showing how to set it up in a Samsung heat pump. Have great day!

Mars 5 December 2020 - 17:58

That’s a great feature. I’ll ask our manufacturers if this feature exists or is in the pipeline for our pump?

George 7 December 2020 - 10:15

For November our 14kw ecodan and 500l cylinder total consumption was 1350.6kWh up from 1164.6 from October. Its running on a weather compensation setting so the flow temp is higher than October.

Is there a particular reason for the current electricity supplier as your unit rate is quite high. Providers are currently offering 10.8p if you shop around which makes quite a difference when running a heat pump over winter. Our costs for November were £160.72

Do you run the log burner(s) every day? We have ours on every night and if its a windy day we start it up around lunch time.

Mars 7 December 2020 - 11:30

Thanks George. Very interesting numbers. I’ll ask GES if their pumps have a weather compensation feature.

I’ve hunted around for a better rate and can’t find a single provider below 15p. Who are you using?

Regarding the wood burners, yes, they go on almost every evening now to give the downstairs a boost.

George 7 December 2020 - 12:04

We currently use Symbio and they are offering a variable contract or fixed 12 month term for 10.8p

The customer support is non existent but if you always remember to submit your reading each month you shouldn’t have a problem.

They also offer variable direct debit billing which I prefer as we pay for exactly what we use each month and they adjust your direct debit each month after you submit a meter reading instead of being charged £200 a month every month and waiting ages for it to balance out.

Mars 7 December 2020 - 12:47

Thanks George. I’ll check them out today.

Mars 7 December 2020 - 15:30

What a great find and suggestion George. I’d looked at the usual comparison sites and they never came up. I’ve just initiated the switch. Extremely competitive kWh rate and standing rate. Thank you for sharing this with us.

Sue Charter 9 December 2020 - 15:08

Hi we had a 12kW NIBE ASHP installed in Oct 2020 to 4 bed barn conversion 150sqm in Ripley, Surrey. I started by setting the system to drop back to 16 degrees overnight then up to 20 in main living area, 18 in bedrooms, it’s now just drops by a degree overnight but struggles to hit 20 by midday on the cold days. I wasn’t convinced to run the system at our top temp for 24 hours a day as the nights are much colder and therefore require more work to maintain but I was told by the installer it’s still more efficient to keep to a set temperature all day. It sounds like this is what you do but I wondered if you had arrived at that decision by trying different options and looking at cost? Great site by the way, try interesting read.

Mars 9 December 2020 - 22:14

Thanks for the feedback and comment Sue.

We are able to maintain 80% of our house at 21C, with a few rooms that are not coming to temperature as a result of plumbing.

We have tried loads of different combinations and scenarios, with a lot of trial and error, and we’ve discovered that running the ASHP 24/7 at a higher temperature is the way to go, as opposed to dropping and spiking the temperature..

The ‘recovery’ in your case from 16 to 20C is quite a big ask for an ASHP, and from our experience wouldn’t be efficient. I’d suggest running it 24/7 on 19-20C in your living area (based on what feels comfortable), and just watch and monitor the electricity consumption on your metres. In our case, running 24/7 at 20C or 21C made absolutely no difference. This week, we’ve raised our temperatures downstairs to 22C, with no significant increase in electricity consumption.

I hope that helps. Please keep us updated and let us know how you get along.

Sue Charter 10 December 2020 - 18:30

Thank you Mars. We have also installed 6KW of solar panels with Solar Edge so, like you, I have a handy display which shows all consumption. The spikes have definitely dropped over the last two days as I’m now only running with a 1 degree difference between night and day. I’ll give it a week and then try constant temp.

I can see how much we are consuming and assume this relates to what we are using to power everything including the air source but I don’t have any means of seeing what I’m really needing as you do. So I can’t calculate a coefficient or have I got that wrong?

My other thought is that I want to make sure that all excess solar power goes to heat water and not have the ASHP jump in. In winter there’s little or no excess but as we get into warmer months I want to restrict the ASHP from heating water in daylight hours and only top up at night. Is this something you have satisfactorily configured?

Thanks again.

Mars 10 December 2020 - 22:13

Thanks for the update Sue.

The SolarEdge app is excellent for monitoring overall consumption. You are correct: the SolarEdge app shows all consumption like the fridge, ASHP, lights, etc. Massive spikes, 95% of the time are the ASHP.

Did you apply for the RHI scheme? We did, and as part of the requirements we had two metres installed; one that only shows electricity consumption for the ASHP and one that shows heat generated. So it’s super easy for us to work out. We also know, in real time, how much power we are using and how much heat we’re generating.

Without these metres it’ll be tough to work COP out. Which brand ASHP do you have? Some pumps have control panels that monitor this data. Ours has additional data we can pull that shows how much power the pump uses on a daily basis.

For the hot water, we installed a gadget called the Solar iBoost. This sends all excess solar production to the hot water and doesn’t send it to grid and we’ve set it to heat to 60C to also deal with the legionnaires cycle. Only after water is at 60C does electricity go back to the grid. It’s worked very well for us. We speak about it in this video:

The iBoost does exactly what you want. Our hot water from April to September is heated by the iBoost alone.

Sue Charter 11 December 2020 - 15:49

Hi Mars,

Our supplier/installer GreenSquare in Bramley are managing the RHI application currently. I’ve raised the meter question with them but looking at the Ofgem site it suggests your payment meter is needed because you have the back up oil boiler and we don’t have that. Ours was removed because it needed replacing. The performance meter is the one I’m not sure about, hopefully I’ll get a response soon. is the page I found.

We have a NIBE 12kw system. I’ve also asked our supplier about calculations the COP.

On hot water, we have an eddi which is the same as an iBoost I believe. However, today I noticed we exported a very small amount of energy and I don’t want to export anything in winter. You seem to be sure that iBoost doesn’t get beaten to your hot water tank by the air source. With the old oil boiler I can just switch the hot water off in the day and get it to come on early evening to top up. With the air source I haven’t yet discovered how to do this or even if I need to do this. Again, I’ve contacted both my solar supplier and GreenSquare for best solution today. The tank must be hot to capacity if I am exporting so I’m thinking the air source programmed to heat hot water full time – I’ll do a bit more research!

Mars 13 December 2020 - 21:44

You are spot on Sue. You only need both metres if you’ve retained an old boiler as a backup, which we did.

That does complicate your COP calculation – does your metre only provide a heat output reading in kWh? If so, you should be OK because your pump must have a consumption log of how much power was used to drive the compressor.

Pertaining to exporting, how hot are you allowing your tank to get? We also export small amounts at this time of year.

Our iBoost does get beaten to heating the hot water by the ASHP because our system is set up to heat hot water over central heating. So if we have early morning showers, the water will get reheated before there’s any solar around. There appears to be no setting on our system to override this. It appears to be the same in your case. It may have something to do with defrost cycles.

You can, however, adjust your hot water to say 42C and let your eddi get it hotter to 60, thereby using more solar. That’s the way we’ve set ours up.

Sue Charter 22 December 2020 - 13:18

Hi Mars,

Yes the meter is a 2nd generation one and does give KwH. Since your last message I’ve talked to all parties and we are now upgrading some radiators as they recommended, installing a new one on a mezzanine floor and had confirmation that we are fully compliant with RHI. The installers have raised the tank temp by another degree which will get tested on Xmas day when the outdoor temp drops but we are running comfortably at the moment. From your advise on the 10th on keeping temps constant we have used considerably less energy so thank you.

On the water front, it’s been suggested that I can schedule the air source hot water to give the solar full control over daylight hours. Our system blasts the temp to 60 degrees once a week overnight so I’m pondering your suggestion vs just switching off the hot water element during the day. It’s not an issue at the moment but maybe I’ll try a few variants and see how it works out.

I hope that you and your family have a lovely Xmas and thank you again for your responses and advice.

Mars 28 December 2020 - 09:48

Thanks for the update Sue and we’re glad to hear that running your pump at consistent temperatures is working better and more efficiently for you.

Please let us know what you decide about your hot water, and how that works out for you.

All the best to you and your family in 2021.

Sue+Charter 9 March 2021 - 19:32

Hi Mars, you asked me to let you know about the hot water – I asked some questions and checked the wiring options with the Eddi and what seems to make sense to me, but yet to be proven, is to schedule the heat pump for hot water to be on only when the solar panels are normally active i.e 830am to 630pm. My logic is that any excess power during the day (and we did have plenty on the warmer sunnier days recently) should power the heat pump to heat the water as it is a far more efficient way to heat water than the immersion, any further excess should then increase the water temp of the hot water using the immersion over and above the temp reached by the heat pump towards 60C max. Any further excess will be exported. My reason for disabling the heat pump hot water overnight means that our small use in the evening will not be recovered until the following day when the panels activate again. This latter part is geared at warmer months as a way of limiting the heat pumps use of mains electric as far as hot water is concerned.

The Eddi is wired to give the heat pump priority – Option 13 in this manual

I think adjustment on scheduling over the year will happen especially if we don’t have enough hot water in the mornings or I’ll just not close down at night to see if there’s any real difference – possibly not. The key fact I hadn’t twigged when we last spoke is that the heat pump makes more efficient use of the excess than the immersion so I just need to let it sort itself out and monitor.

Kind regards,


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