Slash Your Heat Pump Bills Overnight

SCOP vs. savings

As a homeowner and a seasoned heat pump installer with over 15 years of experience, I’ve come to a critical realisation: chasing the highest Coefficient of Performance (COP) and Seasonal Coefficient of Performance (SCOP) isn’t always the path to the most cost-effective heating system. Instead, it’s about being shrewd with the resources at hand. The quest for super efficiency can often feel like a pursuit reserved for the few who own a passive-style, superbly insulated home. But what about the rest of us?

Let me share a personal insight: my house is your average home. Despite my expertise, achieving a heating cost of £1 a day with my heat pump remains elusive. The perfect blend of insulation, solar input, and battery storage needed to attain that super COP/SCOP isn’t part of my reality.

Here’s my strategy: I exploit cheaper electricity tariffs to run my heat pump more intensively, then dial it back during peak tariff hours. It’s a balance of economics over efficiency. For instance, heating water to 60 degrees overnight when electricity costs less may lower my COP, but the kWh price is right. The water stays warmer for longer, potentially sparing me from a pricey reheat during the day.

This tactic extends to home heating. I preheat my house at a higher flow temperature in the wee hours when the tariff hits rock bottom. Sure, my system’s COP takes a hit, but my bank account thanks me.

Take a look at the figures I’ve laid out:

  • At a low rate, the cost of running my heat pump with 10 kWh input is just £0.90, while at a high rate, it jumps to £3.50.
  • As I increase my kWh input, the cost savings between low and high rates become even more pronounced, doubling with every additional 10 kWh.

It’s crucial to understand that not all heat pumps can gracefully modulate to the whims of changing seasons. And, frankly, the COP/SCOP is a metric that doesn’t translate uniformly across all homes, affected by varying ambient conditions and the specific characteristics of each heat pump.

In my professional journey, I’ve never seen a better time to install a heat pump. They’ve evolved to be incredibly quiet, reliable, and sophisticated—truly ready for the future. Yet, I must admit, the current regulations haven’t kept pace with these innovations, often making installations more cumbersome than necessary.

In conclusion, while a high COP/SCOP is admirable, it’s not the be-all and end-all for everyone. By leveraging cheaper electricity tariffs and managing your heat pump’s operation times, you can achieve a harmonious balance between efficiency and economy. This is how I’ve optimized my system at home, and it could very well be the approach that works for you too.

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HughF
2676 kWhs
22 days ago

The only things that matters to me – 1. It doesn’t cost more to run than the gas boiler we replaced, 2. The house is as warm or warmer.
We’ve succeeded on both counts. Warmer house, doesn’t cost any more.
Nothing else matters… Don’t know what my COP is, don’t really care.

Andris
937 kWhs
22 days ago

I absolutely agree! I made huge savings since cheaper tariffs were avaliable at night. I shift just like you. Push it a bit harder when it is cheap. 
This is one of the reason I am so glad we oversized our heatpump a little. I push it hard over a short period. Only need to heate once and the house stays warm throughout. My house is around 21-23c all day. 

mjr
mjr
1920 kWhs
22 days ago


I made huge savings since cheaper tariffs were avaliable at night.

I’m saving even more since switching to a tariff with a cheap rate in the early afternoon, with less of the disruption of the home getting too hot while I’m asleep.

Majordennisbloodnok
3251 kWhs
22 days ago

In an ideal world, we still have to look at efficiency as well in order to avoid the “my comfort is paramount and the climate be damned" attitude. However, one needs to be in quite a privileged position to be able to follow a route that is the best environmentally but costs more. As a result, I wouldn’t feel comfortable criticising anyone for finding a compromise that responsibly balances cost and efficiency.
But the key word there is balance. The situation @Ken Bone has outlined seems to me eminently sensible and reasonable; after all, electricity is cheaper at certain times for a good reason and making use of it during those times instead of peak times has its own altruistic benefits.

Abernyte
2204 kWhs
22 days ago

Those of us who inhabit the Twilight Zone where a smart meter signal has yet to arrive (along with 2G,3G, and 4G signals) must pursue efficiency and lower costs by a different route. I agree that fixation with COP and SCOP does not help so being imaginative with avoiding the coldest periods for boosting the HP’s work load is key, that and a large heat pump!

mjr
mjr
1920 kWhs
22 days ago


In an ideal world, we still have to look at efficiency as well in order to avoid the “my comfort is paramount and the climate be damned" attitude.

Isn’t cost on a time-of-use tariff now partly a representation of how renewable the electricity is at that time? Being more efficient but using more electricity from coal power stations is probably worse for the climate.

Majordennisbloodnok
Reply to  mjr
22 days ago



In an ideal world, we still have to look at efficiency as well in order to avoid the “my comfort is paramount and the climate be damned" attitude.

Isn’t cost on a time-of-use tariff now partly a representation of how renewable the electricity is at that time? Being more efficient but using more electricity from coal power stations is probably worse for the climate.

Absolutely, hence the “as well as". But you’re right; it’s not just about efficiency any more than it should be just about cost. Once again, the right balance is the key.
 

cathodeRay
Editor
6509 kWhs
22 days ago

Another point to consider: what happens if time of use tariffs become commonplace, and many more people time their electricity use according to their tariff? What if demand in peak periods falls, and rises in non-peak periods? Given the fact an ASHP will be the major electricity consumer in most settings that have an ASHP, shifting their use to off-peak periods might substantially reduce peak load and increase off peak load, and in so doing remove the basis for time of use tariffs…

Domestic energy use is second only to transport use, and much of that domestic energy use will be used for heating:

image

Source:

 

SUNandAIR
2363 kWhs
21 days ago


It’s crucial to understand that not all heat pumps can gracefully modulate to the whims of changing seasons. And, frankly, the COP/SCOP is a metric that doesn’t translate uniformly across all homes, affected by varying ambient conditions and the specific characteristics of each heat pump.

Sorry, I have to say this post simply serves to muddy the waters. 
I agree that the time of use tariffs may produce savings as a tactic. But in no way can it be seen as a replacement for efficient installation and commissioning. And latterly efficient operation through low and slow heating strategy. TOU tariffs are not a strategy they are a possibly short lived tactic which is a good overlay after the system is set up properly.
lm sure you have good intention but I can see an audience who may wish to exploit this kind of scenario. There is no way I want to see another substitute for proper installation being created by simply telling the customer “just use better tariffs”.
Likewise the manufacturers need to stop piecemeal development of controls with ad-hock   upgrades which aren’t user friendly. 
So I see efficient use of TOU tariffs as a good overlay once efficiency of the overall heating system is achieved. Then you probably will have discovered that’s boost overheating is not efficient or necessary.
but you’re right… CoP is not King…. Efficiency is King.

JamesPa
3542 kWhs
Reply to  SUNandAIR
21 days ago

Completely agree good installation is mandatory.
I think its highly likely that ToU tarrifs will persist, they have, after all, been around for at least the last 50 years!.  They are an obvious way to smooth demand.  This reduces the peak, which in turn reduces the (expensive) network capacity needed and any residual need to burn fossil fuels which, unlike most other ways to generate electricity, can be turned on or off easily.
They may well get more sophisticated and less attractive as night time charging of electric cars begins to become significant thus helping with the day/night balance, but I cant see a way to manage demand without ToU tarifs of some type. 
 

DavidAlgarve
335 kWhs
21 days ago

The maths attached to a cost analysis of this approach sounds daunting. 
It seems to me that there are two variables that would need to be evaluated, i.e,
1 How much cheaper is the night time tariff than day time?
2 What is the difference between Daytime & night time temperatures? Surely it is cheaper to extract heat from warmer air?
I am trying to hedge my bets by mainly heating DHW up at night, but having an additional period at the hottest part of the day. 
Then again, I am in the Algarve, so temperatures and night time tarriffs are different to the UK

Gary
647 kWhs
21 days ago

@iancalderbank I just run the downstairs UFH only, so no one gets hot whilst asleep, saves about £1.50 a day in terms of off peak vs peak prices.
Its not a thick slab as its retrofit but today at 4C outside it was enough to prevent the heating coming on for 7 hours.

Andris
937 kWhs
Reply to  Gary
21 days ago

@Gary I am the same. None is cooking upstairs, the radiator is set to everyone comfort max 21. Downstairs UFH is on for about 7 hours 22t concrete  ( hand mixed 💪 back in the day  when we built it, We put 150mm Kingspan under it using 20mm piping for UFH.)
I when I go  to bed usaly is is around 21.2c when I get up it is about 21.8c . As underfloor seems to heat up slow once the heating off temp still rises a bit for a few hours and the concrete giving out the heat till it reaches about 22-22.3c then starts falling by 10 pm is about 21.2c again.
As the heat rises still keep upstairs ok. When the heating comes on it does go to about 19.5 but then the heating kicks in as the flow temp is only about 35c. It takes a while to heat upstairs but always stays comfortable.

mjr
mjr
1920 kWhs
20 days ago


Another point to consider: what happens if time of use tariffs become commonplace, and many more people time their electricity use according to their tariff? What if demand in peak periods falls, and rises in non-peak periods? Given the fact an ASHP will be the major electricity consumer in most settings that have an ASHP, shifting their use to off-peak periods might substantially reduce peak load and increase off peak load, and in so doing remove the basis for time of use tariffs…

I suspect there will always be a peak time for domestic heating need which will always result in some peak/off-peak differential worth reflecting in a time of use tariff. No-one is going to be heating their home only while everyone’s in bed.
If load-shifting was that easy, heavy-using industry would have done it years ago and things like Economy7 would have ended.
Batteries probably have far more potential to change this than varying ASHP time of use.

cathodeRay
Editor
6509 kWhs
20 days ago

No-one is going to be heating their home only while everyone’s in bed.

But that is pretty much what has been proposed in this thread… The point I am making is that if this happens widely, it may mean the tariffs end up changing to make it less attractive.

Batteries are an obvious solution for domestic load balancing, apart from the fact the technology isn’t there for mass market yet, and then there are the problems many choose to ignore, like the 12 year old kids operating in toxic mining conditions, what happens to end of life batteries etc. 

iancalderbank
3454 kWhs
Reply to  cathodeRay
20 days ago

@cathodeRay I don’t think it can happen widely. to be honest I’m a little bit puzzled by the original post. I can see how this works with a large UFH slab (as @Gary and @Andris confirmed) but not any other way.

guthrie
438 kWhs
Reply to  cathodeRay
20 days ago



No-one is going to be heating their home only while everyone’s in bed.

But that is pretty much what has been proposed in this thread… The point I am making is that if this happens widely, it may mean the tariffs end up changing to make it less attractive.
Batteries are an obvious solution for domestic load balancing, apart from the fact the technology isn’t there for mass market yet, and then there are the problems many choose to ignore, like the 12 year old kids operating in toxic mining conditions, what happens to end of life batteries etc. 

I remember discussing this sort of thing years ago with people with varying technical backgrounds.
The first point is that using car batteries for load shedding etc only works if your batteries are good enough to take the extra cycling.  They weren’t back then, they might be in some years time. 
Without specific gvt intervention to specific aims, tariffs will change to meet the need of the company to make profit.  Simple as that, so you can expect lower tariffs only when it suits them, e.g. there is too much wind power.
Finally, I’m sure someone could do the modelling, but it probably isn’t efficient to have 20 million little home batteries for load balancing, somewhat regional setups would probably work better.  I also wonder what the fire rate would be when you get to tens of thousands of home batteries. 
As for the child labour, that is how the world works and is solvable with appropriate political will.
Battery recycling is only an issue because the omnipotent market is not actuall omnipotent and there is always drag and inefficiency, which is where a sensible gvt intervention to get it up and running properly would be a good idea.  E.g. these disposable vapes thing, if you had a deposit scheme that would probably help.  But anyway, battery recycling won’t be a problem soon because once supply chains are setup and so on, there will be proper facilities etc for it.  Money needs to be put into it though. 
 
 

cathodeRay
Editor
6509 kWhs
20 days ago

I’m a little bit puzzled by the original post

You weren’t the only one. There is another recent truly bizarre post here, to which I nearly replied ‘"The broader challenge calls for a collective introspection…" as to how on earth I can get away with posting 486 words of AI generated gibberish which says absolutely nothing’. Perhaps the poster’s name is a clue – Nathan Gambling.

JamesPa
3542 kWhs
20 days ago


Batteries are an obvious solution for domestic load balancing, apart from the fact the technology isn’t there for mass market yet, and then there are the problems many choose to ignore, like the 12 year old kids operating in toxic mining conditions, what happens to end of life batteries etc. 

Even more so given that, in 20years time, we will all have at least one 60kWh battery sitting on the drive.
Seriously electric cars should make an enormous difference to load balancing opportunities, although 5-7pm may well remain a problem.
 

Toodles
3836 kWhs
Reply to  JamesPa
20 days ago

@JamesPa When I had my first Powerwall 2 installed in 2022, my installer suggested I think hard before installing a second unit. I have 8.1 kWp. of solar PV and they thought a second unit would never show any ROI. Though my PV installers knew of my intention to have a heat pump installed soon, they still did not feel that more energy storage would be a benefit. The solar PV provision has not changed but with the NG and energy suppliers encouraging us to ‘load shed’ and also the initiative to support the grid during times of highest demand has, I feel moved the goal posts! Once I had the heat pump installed – I felt doubling my capacity would have multiple advantages. 27kW/h of storage arranged around a TOU tariff would be a good move. Not only do I feel the flexibility of TOU charging rates help reduce costs, I have the comfort of being more resilient in the event of power outages … and the benefit of ‘helping the grid out’ whilst being reimbursed well for doing so goes a fair way towards recouping some of the cost of paying for Mr. Musk’s holidays. 😉 Regards, Toodles.

Above&Beyond
9 days ago

Thanks for sharing your tips on reducing energy bills. One more tip is to make sure you have your thermostat in the right spot. If it’s too close to a fireplace, in direct sunlight, or in a room that’s much cooler or warmer than the rest, it might not get a good read on your home’s overall temperature. This can make your heating or cooling system work harder than it needs to. Moving your thermostat to a place that better represents the average temperature of your home can make a big difference.

PeterR@Saltings
128 kWhs
9 days ago

@Ken Bone
I agree that this approach is more cost effective, but not necessarily the most efficient way to run a heat pump.
I have a 12KW Samsung on the Octopus Cosy Tariff.
I run it for 3 hours 4am to 7am on the off-peak tariff (house is warm when I get up) by setting the timer to a 20C target (it overshoots by 1C), then set it back to 18.5C. On really cold days, it might come on again mid morning for an hour or so. I then set it back to 20C at 1pm, for 3 hours, during the second off peak session (1-4pm), so the house is again warm when I get back from work. I set heating and DHW off 4pm to 7pm as this is the peak period. I then set it to 19.5C at 7pm, and then set back to 18.5C at 10.30pm. The heat pump rarely runs between 10:30pm and 4am which is fine with my neighbours.

IMG 2028

 
So the house average is around 19.5C +/-1C throughout the day and night, getting coolest at 4am and warmest at 4pm. So the majority of the heating effort is done using off peak electricity. 
I also run the dishwasher, washing machine and tumble drier in the off peak windows and this also makes a huge difference to lowering the bills.

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