We will be starting a new self build early next year and would welcome some advise.

It will be a timber frame with hemp-lime 400mm insulation, triple glazed windows and our aim is to be near Passivhaus standards without the certification.

Dealing with DNO currently, have had quotes for both single and 3 phase supplies.

We will need new post and transformer at either 3phase 100kVA at £25k or 1 phase 25kVA at £16k.

Both quotes are eye watering. I've explored other avenues eg. ICP's but they are not interested as it's a relatively small project.

Requirements are;

10kw ASHP.

12Kwh Battery storage.

10.7kw solar panels, and in time, EV fast charger. There will also be a small workshop (hobby).

Electric is our only source of power and I want to export back to the grid. We have been told 16amps per phase.

Wish to future proof but at the same time do not want to over spec.

Any more information needed, please ask.

I have no experience in this so any advise will be much appreciated.

At a first glance, such a measure appears to have a negative impact on the transition to heat pumps, since removing gas entirely and hence no longer paying the standing charge is one benefit of the transition to low carbon heating.

However, the actual impact of such a move very much depends on how the shortfall in revenue is recovered. Currently, the gas standing charges cover: day-to-day operating costs for suppliers including metering services, the warm home discount and green levies, supplier profit and risk management, and leveling costs across different payment methods. 

There are two possible ways to meet the shortfall, the first is to cover the costs through general taxation, the second through increases to unit rates.

There are about 23 million domestic gas meters in the UK, and the standing charge is about £108.30 per year, so the total revenue is about £2.5 billion. This is a lot to cover through general taxation at a time when there are many competing demands on taxpayers money. The alternative is to increase unit rates. Ofgem estimates that the average gas usage is now 9500kWh per year for domestic consumers. Hence shifting the cost of removing the standing charge onto unit rates would increase the latter by about 1.14p per unit. 

How does this help the transition from gas boilers to heat pumps?

In Jan 2027, gas unit prices are forecast to be 9.76p with electricity unit prices at 30.28p (Cornwall Insight). Removing the gas standing charge and recovering the lost revenues through higher unit rates would lead to prices of 10.9p per unit for gas and 30.28p per unit for electricity. This gives a spark gap of 2.78, much less than previously.

Assuming that an air-to water heat pump can be run 50% on half price electricity and 50% on full price electricity (a reasonably conservative assumption about time of use tariffs) and that the achieved efficiency is 3.5 (a stretch but not impossible) and a gas boiler has an efficiency of 0.9, we have the following:

Gas heating cost per year for 9500 kWh input is 0.109 x 9500 = £1035.50

Heat pump heating cost per year for 9500 x 0.9 kWh output is (0.75 x 30.28) x 9500 x 0.9 / 3.5 = £554.78

Saving is £480.72

Over a 15 year life, that amounts to a saving of £7210. 

This is getting close to the level at which Govt could replace the BUS grant with an interest free loan for all of the costs of a heat pump upgrade, repayable over the lifetime of the heat pump (15 years). The saving in energy bills during that time would contribute over £7200 on top of the cost of around £3000 for a new gas boiler, so £10k to fit a heat pump and be overall cost neutral versus gas. This is the sort of argument that could just about work.

To really make it work, steps would need to be taken to ensure that the spark gap does not creep up above 2.8 again. This could be done by loading more costs onto gas unit prices - for example 20% VAT rather than 5% and use the additional revenues to reduce the unit price of electricity. This would leave Ofgem average customers no worse off overall, but create a stronger incentive to transition to low carbon heating.

It will be interesting to see what steps Govt takes in this area in next week's budget.

That got me thinking about the more substantial equipment we are increasingly connecting to our homes, particularly heat pumps, batteries, solar PV systems and EV chargers, because I would be interested to know how much control everyone actually retains when their broadband disappears. With our own experience, the dependence on an internet connection has become apparent through everyday inconvenience, but what would happen if you needed to change your heating, get a tank of hot water ready or charge the car for an unexpected journey, and the app you normally use could no longer communicate with the equipment?

For those with heat pumps, what can you do directly from the controller in your house when there is no internet connection, and have you actually had to use it under those circumstances? Can you turn the heating on or off, change the temperature and request a hot water boost, and can you override a schedule that was originally created through an app? I am particularly curious about where those schedules actually live too, whether the heat pump remembers and follows them independently, whether you can edit them locally and whether an instruction previously sent through an app leaves you hunting through controller menus to work out how to change it.

I would also love to hear the same from people with batteries, especially where charging and discharging are managed around electricity prices or an external optimisation service, because there are several different things that could matter during an outage. Does your battery carry on following its existing settings, can you change charging times or the minimum charge you want to keep from controls available at home, and what happens to any arrangements that normally depend on receiving fresh instructions over the internet? With solar PV, I would also be interested to hear whether losing connectivity simply leaves a gap in your monitoring or affects any of the controls you normally use to manage the wider system. 

EV charging raises yet another set of practical questions, particularly if your usual routine involves an app, a scheduled charging window or instructions from your electricity supplier. If the internet goes down and you suddenly need the car charged, can you walk outside, press a button and get it charging, or do you need to find another way to override the existing arrangements? Where several systems work together, such as a charger using surplus solar or a home energy management system coordinating the heat pump and battery, which parts continue doing their job and which parts lose their ability to respond?

Please share what equipment you have, how you normally control it and what you can still do when the internet is unavailable, particularly if you have experienced an outage and discovered either a useful fallback or an unexpected limitation. I would also be interested to know whether your installer explained any of this at handover, whether everyone in the household knows how to use the local controls and whether restoring the connection gets everything working again without intervention.

After two days of discovering how much administration can sit between a person and a 'smart' light bulb, I am keen to understand how well our renewable systems cope when the internet stops cooperating. The last two days have been alarmingly revealing.

I have always hated switching broadband providers because so much of my work depends on having a reliable connection, but after being assured by Plusnet that the whole thing would be seamless and easy, we reluctantly decided to go ahead. We are, after all, in 2026, the fibre is already installed and we had a perfectly good connection before any of this started, so I allowed myself to believe that changing the company taking our direct debit might be a reasonably straightforward exercise.

BT managed to disconnect us in the early hours of Monday morning with surgical precision, while Plusnet said we would be up and running that day, so out came the old router and in went what looks remarkably like the same router wearing a Plusnet badge. Monday passed without anything happening, and when I checked this morning, the website had replaced its previous message with We’re really sorry there’s been a delay with your installation. 

I then spent almost an hour on the phone to Plusnet, and I will give them credit for having someone in Sheffield available to speak to (unlike reaching BT that entails speaking with chatbots headquartered out of India), although the conversation became increasingly frustrating as we worked our way through several escalations. Apparently, Openreach is the issue, BT was also brought into the discussion at one stage, and the eventual answer was that Openreach had been contacted and the switch could take up to another 48 hours. I must say the UK has mastered blaming someone else, and I probably found disconcerting is that everyone I spoke to didn't really have an answer or could provide any assurance. Given it's 2026 l said earlier, I'm staggered that this process is more transparent.

I appreciate that technical problems happen, but our connection was working before the switch, and nobody has given us a clear explanation of what has changed or what needs to happen to restore it. We live rurally, our 5G coverage is patchy and fibre is a substantial part of how I earn a living, so losing it means rearranging work around an unreliable mobile connection while waiting for an update that might or might not move things forward.

The saving is still worth having, but this is exactly why I was reluctant to switch in the first place, and every passing hour makes those assurances about an easy, seamless handover feel a little more ambitious. Somewhere between BT switching us off, Plusnet switching us on and Openreach doing whatever is required in between, somebody needs to take responsibility for getting us connected, because I have now spent considerably more time managing this supposedly effortless switch than I spent finding the deal.

Could someone please refresh my memory on how to set/ reset the schedule timer to achieve this?

For house heating I have a weather compensation curve and will operate 24 hours  

Last night at 23:00, the house temperature was 22.6c and the heating hadn’t been on all day because it was warm enough to heat the house from just the sun. OAT dropped to 6.2c (reported by the Cosy unit) at 03:30 with the house temperature at 21.2c.  At 07:30, the house was at 21.7c and it finally reached 22c at around 09:30 when the OAT had reached 9.5c.  It took 6 hours to raise the temperature by 1c.

My flow temperatures are 50c@-10c OAT and 33c@12c OAT.  This is a drop from 36c@12c OAT I ran last year.  As far as I know the WC curve is linear.  At that flow temperature setting, the house can reach temp and I have to say it is more comfortable for having the heating on for that time period because the internal air actually feels warm.

Is there any consensus on how long you would want to take to warm up by 1c?  Is there anything in the above that says I may have dropped the flow temperature too far given it’s likely to get colder? Perhaps there is scope to drop the flow temperature further?  Really it’s more a discussion point than an actual query: if it meets temperature, we are comfortable and it isn’t costing the earth then all is good right!

Remember, Octopus control their Cosy units via a thermostat with the hysteresis set to -0.1c to +0.2c.  So with a setting of 22c, heating comes on at 21.9c and off at 22.2c.  These are reported temperatures of course, I doubt the sensors are that accurate!

On a semi-related subject, I’m inclined to think it isn’t worth doing a setback for just 3.5hours.  I suppose then it becomes more a question of whether the flow temperature is sufficient to recover from the 1hr water heat cycle when it is colder.

Heat pump suppliers recommend buffer tanks as they greatly simplify the installation for installers and they help protect the manufacturer against warranty/ installation issues as a result.  It works, but buffertank systems cost more, they reduce efficiency, and they are often simply not needed.

Design - Ensure system thermal mass and/or heat exchange is sufficient.  This mass / exchange can be from any combination of system water volume, mass volume (concrete in a hydronic slab), or heat exchanger capacity (ability to exchange heat).  As long as the heat pump can exchange enough heat it won’t short cycle .. this is physics 101.

Sizing - Many installers in the HVAC industry are used to oversizing gas furnaces by anywhere from 20-50%.  This is fine for a gas furnace, but heat pumps should be sized for the minimum justifiable load.  Oversized units cost more to run and they will likely short cycle.  In very cold regions like Alberta, back up heat is necessary anyway for when conditions fall below -35C.  For economic efficiency, it is actually better to use -20C as the cutoff as COP drops below 2 typically at this temperature.  In Alberta, 90% of the seasonal BTU heating load is above -20C (this is accurate btw).

Controls - Heat pumps use different strategies and controllers to turn on / off and modulate.  When using a buffer tank, the heat pump heats water to a target tank temperature and then turns off once the tank reaches the target temperature.  In a bufferless system, installers will either place the buffer tank’s sensor onto the return water line, or just ignore it and leave it in the unit.  Either way tank temperature is arbitrarily set high so that it is never reached. Set this way, the HP would never turn off .. instead, a home thermostat is used to control the on- off function and the return water line is used to modulate output.  Ambient temperature modulation curves are in turn linked to return water temperature.

Zones - bufferless systems work best in simple, full flow designs with one circulating pump for the whole system.  No zones, no extra pumps, no /few auto valves, etc.  You try to set / balance your flows mechanically to ensure the system always has full flow available.  This is a “must” as the system needs to be ready to exchange heat at any time .. especially for defrost cycles where the system will run at full capacity.

On/Off hybrid system control - Depending on your HP, it may have sufficient ambient temperature control and features to not even need an on/off thermostat.  If it needs one, here are some solutions.

You can set up separate thermostats to run both the HP and gas furnace or use just one.  How you set this up will vary by your HP controller and thermostat logic.  For the system I just installed in Alberta I used a separate thermostat for the gas furnace and simply set it 1C lower than the HP so it performs as a “peaker”.  This is not ideal as both units could run at the same time and this can cause too much heat / errors depending on your design.  A better solution is to use one thermostat or system to coordinate both units.

You may find you need to use a dual transformer compatible / high DT thermostat in this case (like an Ecobee Premium), and you may find that you need to wire the thermostat W1 and Y to the same on/off switch on your HP unless your HP controller has both terminals.  The cheap Chinese unit I just installed didn’t.  If you do this, the current will probably backfeed and cause damage to your HP and/or thermostat.  A cheat is to install diodes on W1 and Y to prevent backfeeding the circuit.  A better solution is to wire W1 and Y to separate dry contact relays to control the HP.  OB control (reversing valve) may be switched manually / seasonally or it may be automated depending on your HP.  Good luck!

I'm no HVAC professional, but have been very interested in GSHP systems since the early 2000's.

A concept my mind has been playing with (mainly to reduce installation expenses, and maybe increase efficiency is to use underground liquid tanks instead of ground or water loops.

My specific idea is (for a 3 Ton pump) to have two ±20,000 liter underground tanks, at a good distance from each other. Instead of using one source for all temperatures, have one designated hot liquid tank, and one cold / ice tank.

To further mitigate the risk of everything freezing up, I'm thinking to connect a set of evacuated solar tubes to heat the hot liquid, and connect the hot and cold tank with mixing valves so temp can be kept at ideal temperature.

The benefit of this would be that you can freeze the cold tank at the end of winter, and use this energy for cooling in early spring, while hot tanks should be warm enough by then to provide a bit of heat if needed. In the fall the reversed process will be used. I figure you may be able to completely turn the heat pump off for a month or so in the spring and fall ...   

As said I am no pro, but this idea is stuck in my mind for over a year now ... Am I onto something, or are some of my ideas not realistic? I'm looking forward to your professional opinions, for which big thanks in advance!