Welcome to the forum, @fleecy.

That's an interesting set of questions, but I have to start with one of my own. Is there a particular reason why you want to replace your wet central heating with electric storage heaters rather than investigate the possibility of a heat pump? If you have a battery and inverter - even more so with solar panels as well - you certainly have the building blocks for moving to a more interesting tariff and probably reduce your average cost per kWh to a point that heat pump efficiency starts to really overshadow the cost of gas, so I'm intrigued why you'd want to move from a 90% (ish) efficient gas boiler to a 90% (ish) efficient storage heater instead of a 350% (ish) efficient heat pump.

@fleecy There is a range within the Sunamp Thermino armoury that uses solar and or grid power. We have the Epc210 version and a Myenergi Eddi to do the power diversion. At this time of the year, solar power does all the heating for us and for the two of us showering and washing but no bath, plus use at kitchen and bathroom sink. Currently, we are using just under 3 kWh per day and have the equivalent of 210 litres of HW (hence the name. There are various sizes or capacities in the range; we chose a Sunamp Thermino Epc model as we don’t have space for the 200 + litre tank MCS specify for a ‘4 bedroomed house’. I should emphasise with our low HW usage, we only use a small proportion of the units’ capacity. We are an all-electric household with a Daikin Altherma 3 heat pump for space heating only, leaving the Sunamp to deal with all DHW needs. Regards, Toodles.

Having just ripped out storage heaters and fitted radiators ready for installation of a heatpump, I think your approach would be unusual/madness unless you have a massive solar array and battery capable of covering your mid winter usage over continuous cloudy days or under snow cover.

Backing yourself into a corner with 1Kw of energy producing 1kw of heat, when theres devices which use 1kw of energy and gather between 3 and 5kw of heat.

Is your existing pipework and radiators really that unsuitable, that a heatpump wouldn't work

You're already contemplating a mixergy cylinder, and a heatpump could heat that, or any other large coil area cylinder.

Is your existing pipework and radiators really that unsuitable, that a heatpump wouldn't work?

*CORRECTION* Epv210 is what I should have written. Apologies, Toodles.

Posted by: @singlespeed

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Is your existing pipework and radiators really that unsuitable, that a heatpump wouldn't work?

Even if they were an air/air system would be astronomically cheaper to run.

Hi, thanks for all the great input. I'll explain a bit more about my decision. First off, we have an 8kw and 13.4 kwh AlphaESS system but that is neither here nor there for the choice of heating and water. I did look at heat pumps for a long time but decided to go a different route for the following reasons.

1) the rads and pipework all needs replacing.

2) we live 200m from the fylde coast and speaking to neighbours around here, they have had big issues with salt corrosion and sand egress into their heat pumps. 1 person even went so far as to install the heat pump in his not-used garage with some vents for air in/out but he had only just done that and I don't have that much spare space.

3) I have never had a decent fluid rad system in any house. Radiators would be on when the valves were off or the other way around; rooms would be freezing when they should be warm; rooms would be warm when no one was in them; the timing schedules never seemed to work properly, or would work properly for a bit and then not etc. I just want per room control and these ecostrad iq ceramic radiators do that, with features like detect whether a person is in the room, detect open doors/windows and thermal mass storage etc. 

4) with PV and cheap night tariffs, I can fill my batteries at night with cheap electricity and use it during the day (and yes I could use that to drive a heat pump as well).

5) I'm going to need a HW cylinder or some sort of water heating solution anyway.

I may come to regret the choice re heating but we'll see. Life is an adventure and I'll report back on how it goes. Thanks for all the info re water systems and heating. It is that I need to focus on now and if others have any more information, please let me know 😎

@toodles that sounds like something I could go with. I essentially want to swap like (gas) for like (electricity), keeping the same HW on demand solution around the house. Most of the time, it is just me and Kay here so it's not like a multi-kid house with loads of showers on for hours at a time 😉 thanks

@fleecy We had a gas boiler with a 99 litre HW tank, both in the airing cupboard. To comply with MCS guidelines (and enjoy the £5,000 grant) when fitting a heat pump we were required to find space for a 210 litre tank - this really was not possible for us.

There are Sunamp systems for heat pumps but require High Temperature pumps and we did not wish to fit an HT heat pump; hence our choice of the solar / grid powered version (Epv type). Some readers have written about the cost of such a system and others have mentioned the greater efficiency obtained when using ~350% or higher COP of heat pumps but, space did not permit a large tank and we do have solar power which powers the system for a fair proportion of the year. We didn’t have the space and Sunamp is a solution! Regards, Toodles.

The problem you hit with batteries and electric radiators is they are 4 x less efficient than say an air/air heatpump. That means you need vastly bigger batteries which means you need a much bigger inverter and the pound signs keep going up and up, or you pay for a lot of electricity and the bills go up even faster.

That aside from the water perspective the two are pretty much independent in the non air/water case. There is kit that does both but it's pretty leading edge. We actually went for the complete other end of the spectrum. Our water usage isn't particularly high so the heating went air/air but most of the water is heated by a good old fashioned immersion over night and we sometimes dump some solar into it if the batteries fill. In that case because of overnight low tariffs the heatpump payback was not good enough. If the day/night prices begin to get less polarised then I suspect we'll eventually have to revisit that choice.

@etchedpixels Yeah, I may live to regret the HP v Electric Rads decision. Makes me wonder though, if an HP uses less energy than it generates, what the issues with it having generate electricity instead of hot water, or is the water it heats for the radiators not hot enough to generate electricity?

Posted by: @fleecy

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we live 200m from the fylde coast and speaking to neighbours around here, they have had big issues with salt corrosion and sand egress into their heat pumps. 1 person even went so far as to install the heat pump in his not-used garage with some vents for air in/out but he had only just done that and I don't have that much spare space.

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One thing that strikes me is that unless you have an unusually high density of installed heat pumps around you, talking with the neighbours still only means canvassing a small number of opinions that could be thought of as "informed". If it's only two or three, that's easily few enough opinions to be influenced by other factors (such as bad or mediocre installers).

I absolutely agree with your approach of asking people who already have heat pumps, but you might want to get onto the Visit a Heat Pump web site and see if you can't meet up with a few more people with heat pumps who can give their opinions to add to your information gathering. At worst, you end up wasting a few trips out and get to the same conclusion. At best, you may find a heat pump is a reasonable alternative after all, and just possibly you might even get some tips on how to get a heat pump installed in such a way as to avoid sand ingress and salt corrosion.

I should also point out that we have an awful lot of coastline in the UK and there are a lot of heat pumps installed in that environment - even amongst this forum's members. I cannot believe yours is a situation that hasn't been addressed before, so the information's out there.