Why heat pump and Agile were made for each other
Heat pumps and time-of-use electricity tariffs were built for each other, even if most installers never explain this. Understanding why requires understanding two things about heat pumps that most homeowners do not know.
First: a heat pump does not heat instantaneously. Unlike a gas boiler that fires up and produces heat within minutes, a heat pump works gradually. It moves heat from outside air into your home slowly and continuously. This is not a limitation - it is an advantage. A slow, continuous process can be run at any time of day or night. It is highly schedulable.
Second: buildings have thermal mass. Stone walls, concrete floors, and the general fabric of a home absorb and store heat. A well-insulated house that is warmed overnight to 20 degrees does not immediately return to outdoor temperatures when the heat pump switches off. It stays warm for hours. The heat stored in the building fabric acts as a battery - a free thermal battery that costs nothing to build and nothing to maintain.
These two facts combine to create a compelling strategy. Run the heat pump overnight, when Octopus Agile prices are at their lowest. Warm the building mass during the cheapest electricity hours. Let the stored heat carry the home through the morning peak, when electricity is most expensive. By the time prices drop again in the afternoon, the top-up requirement is modest.
The result: £150 to £300 in annual savings compared to running the same heat pump on a flat-rate tariff, simply through smarter scheduling. The heat pump itself does not change. The energy delivered to your home does not change. Only the timing changes - and timing is everything on Octopus Agile.
How much does a heat pump cost to run on Agile? The real numbers
Heat pump efficiency is measured by its Coefficient of Performance (COP). A COP of 3 means the heat pump produces 3 kilowatt hours of heat for every 1 kilowatt hour of electricity consumed. This is not a theoretical figure - modern air source heat pumps achieve COP of 2.5 to 4.5 depending on conditions, with 3 being a reasonable real-world average for a well-installed system in a UK climate.
Now apply Octopus Agile pricing. At 3p per kilowatt hour overnight - achievable on many nights from October through April - the calculation becomes striking:
| Electricity rate | Heat pump COP | Effective cost per kWh of heat | Equivalent gas cost |
|---|---|---|---|
| 3p/kWh (overnight Agile) | 3.0 | 1p per kWh heat | Gas at ~7p/kWh |
| 8p/kWh (overnight Agile) | 3.0 | 2.7p per kWh heat | Gas at ~7p/kWh |
| 26p/kWh (price cap rate) | 3.0 | 8.7p per kWh heat | Gas at ~7p/kWh |
| 40p/kWh (peak Agile) | 3.0 | 13.3p per kWh heat | Gas at ~7p/kWh |
The lesson is immediate. A heat pump on overnight Agile pricing delivers heat at a cost that gas heating cannot match. The same heat pump running at peak Agile prices costs nearly twice as much as gas. Timing is not a minor optimisation - it determines whether your heat pump is a brilliant investment or an expensive mistake.
For a typical three-bedroom semi-detached home with an annual heating demand of 12,000kWh, shifting even 40% of heat pump operation from peak to overnight Agile hours saves between £150 and £300 per year. Larger homes, or homes with higher thermal mass, save more.
The scheduling strategy: pre-heat overnight, avoid peaks
The core strategy is pre-heating. You set the heat pump to run at a slightly higher target temperature overnight - say 21 or 22 degrees instead of the daytime 19 degrees - during the cheapest Agile windows. The building fabric absorbs this extra heat. When the heat pump switches to a minimal or hold mode in the morning, the stored warmth keeps the home comfortable through the expensive 6am to 9am price period.
The specific pre-heat temperature depends on your home's insulation level. A well-insulated modern home might only need to pre-heat to 21 degrees. An older property with thicker walls and stone construction might actually retain heat better and benefit from a slightly higher pre-heat. Experiment with one or two degrees of variation over a few weeks to find the sweet spot for your building.
The key window to avoid is 5pm to 8pm. This is the peak period on the UK grid. On Octopus Agile, this consistently produces the most expensive half-hourly slots of the day. Running a heat pump flat-out during this window at 35 to 45p per kilowatt hour is the most expensive way to use it. The strategy is to have the building already warm when this window begins, so the heat pump is running at low demand or has switched to a hold-temperature mode.
A practical daily schedule for a heat pump on Agile looks like this. From midnight to 6am: maximum pre-heat, target temperature 21 to 22 degrees, heat pump running continuously to build stored warmth in the building. From 6am to 4pm: maintain target temperature at normal comfort level, heat pump running as needed at moderate electricity prices. From 4pm to 8pm: switch to hold mode, target temperature dropped one degree, let the stored warmth from overnight carry the building. From 8pm onwards: moderate operation as evening prices begin to fall.
Weather compensation and COP - why mild nights are goldmines
Heat pump efficiency is not constant. COP varies significantly with outdoor temperature. The smaller the difference between outdoor air temperature and your target flow temperature, the more efficiently a heat pump runs. This relationship is fundamental to understanding when your heat pump delivers the most value on Agile.
In deep winter, outdoor temperatures of -2 to 5 degrees Celsius mean the heat pump is working hard to extract heat from very cold air. COP drops toward 2.0 to 2.5 in these conditions. The heat pump is still cheaper than gas, but the gap narrows.
In mild spring and autumn weather, outdoor temperatures of 8 to 14 degrees mean the heat pump barely has to work. COP rises to 3.5, 4.0, sometimes higher. The heat pump is extraordinarily efficient, producing four units of heat for every unit of electricity consumed.
Now combine mild weather with overnight Agile pricing. A mild October night - outdoor temperature 10 degrees, heat pump COP of 4.0, Agile overnight rate of 4p per kilowatt hour. The effective cost of heat is 1p per kilowatt hour. That is genuinely cheaper than burning anything. Gas, oil, wood pellets - nothing delivers heat at 1p per kilowatt hour.
These nights are not rare. Spring and autumn in the UK provide dozens of them. The heat pump owner on Agile who has set their pre-heat schedule captures every single one. The heat pump owner on a flat-rate tariff pays the same whether it is midnight or 6pm. The savings diverge quietly over thousands of hours of operation.
Modern heat pumps support weather compensation curves, which automatically adjust the flow temperature based on outdoor conditions. When the weather compensation is properly configured, the heat pump runs at lower flow temperatures on mild days, which further boosts COP. This is a setting your installer should configure, but it is worth asking about specifically if they have not mentioned it.
Setting your heat pump schedule: Daikin, Mitsubishi, Samsung, Vaillant
Every major heat pump manufacturer provides scheduling capability. The interface varies, but the goal is the same: set the overnight pre-heat window to align with the cheapest Agile hours, and reduce demand during the 5pm to 8pm peak.
Daikin Altherma
Daikin heat pumps are controlled via the Daikin Online Controller app. Open the app and navigate to Schedules. You can set up to six temperature setpoints per day, each linked to a time. Configure an overnight setpoint of 21 to 22 degrees starting from midnight or 1am, dropping back to a maintenance temperature of 18 degrees from 6am, rising to your normal comfort temperature through the day, and reducing again at 5pm. Daikin also supports domestic hot water scheduling - set hot water cylinder heating to the cheapest overnight Agile window, typically 2am to 4am.
Mitsubishi Ecodan
Mitsubishi Ecodan heat pumps use the MELCloud app for remote scheduling. Navigate to Schedule settings and create a weekly programme. MELCloud supports separate scheduling for space heating and hot water, which is important - you can time the hot water cylinder independently of the space heating and optimise both for the cheapest overnight slots. Set the space heating overnight pre-heat temperature to run from 12:30am to 5:30am, and the hot water boost to run from 2am to 4am.
Samsung EHS (Gen 6 and later)
Samsung heat pumps connect to the SmartThings app. Go to your heat pump device in SmartThings and select Schedule. Samsung supports both quiet mode and an eco mode; enable quiet mode for overnight operation if your heat pump is located close to a bedroom or neighbour's wall. Set the pre-heat schedule to the cheapest Agile window for your region. Samsung's weather compensation is configured through the engineer menu at installation - confirm with your installer that it is enabled and set to the appropriate curve for your home.
Vaillant aroTHERM plus
Vaillant systems use the myVAILLANT app or the physical control unit. In the app, navigate to Heating Zones and then Time Programme. Vaillant supports detailed daily and weekly schedules with different setpoints for each time slot. Set the overnight comfort temperature programme to your pre-heat target for the 1am to 6am window. Vaillant also has a Smart Grid Ready feature that can accept an external signal to switch between normal and boosted operation - if your installation is Smart Grid Ready enabled, this can potentially be automated with Agile price signals in future integrations.
The seasonal approach: summer vs winter scheduling differences
Heat pump scheduling is not the same in every season. The strategy shifts as the heating demand profile changes through the year.
In winter (November to February), the overnight pre-heat strategy works hardest. Long cold nights mean the heat pump needs to run for several hours to build adequate warmth in the building fabric. The overnight cheap window from midnight to 6am is fully used. The 5pm to 8pm peak is consistently the most expensive period of the day and most consistently worth avoiding. The building's thermal mass is working against you to some extent - colder outdoor temperatures mean heat loss from the building is faster, so the pre-heated warmth is depleted more quickly. Extend the overnight pre-heat to the full 6-hour cheap window and use a slightly higher setpoint.
In spring and autumn (March to May, September to October), these are the golden months. Mild outdoor temperatures mean COP is at its best. Agile overnight prices are often very low because wind generation is strong and demand is moderate. The combination of high efficiency and cheap electricity is uniquely powerful. The building retains warmth for longer because heat losses are lower. A shorter pre-heat window - say 2am to 5am at moderate pre-heat temperature - is often sufficient to maintain comfort through the morning peak. Run an analysis on AgileAlert of which overnight slots are cheapest on mild weather days; you will often find three or four consecutive hours below 5p per kilowatt hour.
In summer (June to August), space heating demand drops to near zero across most of the UK. The heat pump's role shifts primarily to domestic hot water heating. Schedule DHW cylinder heating to run once daily, ideally in the early hours of the morning during the cheapest Agile window. A 200-litre hot water cylinder heated from cold requires roughly 4 to 5kWh. At 3p per kilowatt hour, that is 15p per day for all your hot water. Heat the same cylinder at 6pm peak rates and it costs £1.75 to £2.25. The summer saving is not as dramatic as the winter space heating saving, but it is real and it accumulates over months.
Agile vs Octopus Cosy for heat pump users
Heat pump owners considering time-of-use tariffs often compare Octopus Agile against Octopus Cosy, which is specifically designed for heat pump households. Understanding the genuine trade-offs matters before you commit.
Octopus Cosy offers fixed cheap periods every day: 4am to 7am and 1pm to 4pm. These are predictable. You know exactly when cheap electricity is available, and you can set your heat pump schedule once without ever checking a price dashboard. The daytime window (1pm to 4pm) is particularly useful for heat pump owners because it allows daytime heating to be timed to a cheap period, which is not possible with Agile's overnight focus.
Octopus Agile is dynamic. The cheapest windows vary daily. On a good overnight Agile day, prices in the 2am to 5am window might be 2 to 4p per kilowatt hour - well below the Cosy fixed rate. On a poor day, those same slots might be 10 to 14p. The variation is significant. Agile also offers plunge pricing, which Cosy does not - the ability to earn money when prices go negative is exclusive to Agile.
The practical conclusion for heat pump owners: Agile wins in spring and autumn when wind generation is strong and overnight prices are frequently excellent. The combination of high COP and very cheap electricity in these months is Agile's strongest argument. Cosy has merit in deep winter when consistency matters more than the variable floor. On the coldest nights, when you really need the heat pump running to its full schedule, the predictability of Cosy's fixed windows removes the anxiety of checking whether tonight's Agile prices are acceptable.
Some heat pump owners switch between tariffs seasonally, which Octopus permits. This is a valid approach but adds complexity. For most households, Agile and a well-configured overnight schedule delivers superior economics over the year when averaged across all seasons.
What AgileAlert shows heat pump owners
The most valuable single piece of information for a heat pump owner on Agile is tomorrow's cheapest overnight window. Not the cheapest individual half-hour slot - but the cheapest three-hour or four-hour consecutive window, because pre-heating a building requires continuous operation, not a single cheap slot surrounded by expensive periods.
AgileAlert shows the live half-hourly price schedule for your region, updated every evening when new prices are published. The dashboard lets you see the complete overnight price curve at a glance. Identifying the cheapest three-hour block takes seconds. Set your heat pump timer to that window. On nights when prices are uniformly low, run the full overnight period. On nights when there is a clearly cheaper window in the early hours, set the pre-heat to start and finish within that window.
Over the course of a month, this optimisation means the heat pump's overnight operation consistently aligns with the cheapest available electricity. The cumulative effect on the annual bill is where the £150 to £300 saving figure comes from. It is not dramatic on any single night. It compounds, quietly and reliably, over hundreds of operating hours.
AgileAlert also shows plunge pricing events when they occur. For heat pump owners with hot water cylinders, a plunge pricing event is an immediate trigger to run the DHW boost cycle. A 200-litre cylinder heated during plunge pricing earns a credit on your Octopus account rather than incurring a cost. Capturing even six or eight of these events per year adds £20 to £40 in credits on top of the scheduling saving.