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Electrification and Independent Hot Water Systems Request for Knowledge

 
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Domestic Hot Water & Cylinders
Last Post by Singlespeed 3 weeks ago
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 EtchedPixels
(@etchedpixels)
Estimable Member Member
Joined: 2 months ago
Posts: 124
08/07/2026 10:14 am  

Posted by: @fleecy
↑

@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?

A heat pump moves energy from A to B efficiently, especially if the differentials are low. Trying to generate electricity from heat is very different and needs high temperatures to achieve even 30-40% efficiency. Physics doesn't let you print free money.

 

 



   
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Majordennisbloodnok
 Majordennisbloodnok
(@majordennisbloodnok)
Famed Member Moderator
Joined: 5 years ago
Posts: 1999
08/07/2026 10:20 am  

Posted by: @fleecy
↑

...

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?

That's because it doesn't generate electricity. In fact, it doesn't generate energy at all. All it does is move heat from one place to another, and that process is efficient enough that the energy it needs to do the moving is significantly less than the amount of energy it moves.

You already have a heat pump in your house, so you can see the physics in action. The inside of your fridge is cold, but the coil at the back of it is warm. The fridge isn't cooling per se; it's just moving heat energy from inside to outside and heating your house in the process. Similarly, my heat pump in winter is expending a lot of energy trying to cool Surrey down further, and the heat it removes from the Surrey countryside is dumped into my house. There is a very good introduction to the whole topic at https://renewableheatinghub.co.uk/heat-pump-basics-jargon-free-guide/

 

 


105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and SPH5000 inverter
1 x Myenergi Zappi
1 x VW ID3
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; sumus solum profundum variat"


   
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 fleecy
(@fleecy)
Active Member Member
Joined: 3 weeks ago
Posts: 11
Topic starter 08/07/2026 10:23 am  

@majordennisbloodnok good points. I will do so. Thanks



   
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 fleecy
(@fleecy)
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Joined: 3 weeks ago
Posts: 11
Topic starter 08/07/2026 10:24 am  

Good point. I will do so. Thanks 😎



   
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 EtchedPixels
(@etchedpixels)
Estimable Member Member
Joined: 2 months ago
Posts: 124
08/07/2026 10:39 am  

Posted by: @fleecy
↑

@etchedpixels Yeah, I may live to regret the HP v Electric Rads decision. 

 

Occurs to me you might want to look at the videos by Andrew Till / Mr EV on youtube. He went with the electric heaters but lots of solar/battery choice.

 



   
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 Singlespeed
(@singlespeed)
Active Member Member
Joined: 4 months ago
Posts: 14
08/07/2026 11:36 am  

Posted by: @fleecy
↑

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.

Are your neighbours units specifically designed for coastal areas and are your neighbours regularly rinsing off the unit and its heat exchanger?

In the Findhorn eco village, which is bounded by dunes and close to the Moray Firth, the heatpumps are almost exclusively Mitsubishi Ecodan units which I'm guessing will be the coastal variant.

Would ground source be an option for you? As that would eliminate the external unit.

As I said earlier, I have just removed my storage heaters, two of which were newer dimplex quantum. Resistive heating was expensive to run and the house was only partly heated to a comfortable temperature.... A battery / solar install to cover the heating demands were completely unrealistic. I haven't removed the infrared panels, as they don't interfere with anything and they may be required on very cold days.

Unless your heat demand is ONLY 1kw, your battery isn't going to last the day feeding an electric heater.

 

 



   
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