Flats needing refurbishment.
100-150 square metres.
Refurbishment is a great opportunity to replace the old gas boiler with an electric alternative. Depending on the condition of the heating system and your budget, you have four options:
Install a heat battery boiler, like the Tepeo ZEB, to supply hot water and heating. You remove the existing boiler and plug in this new one.
Well-insulated 100 to 150-square-metre flats should be just within the ZEB's energy capacity. If your property is not well insulated, you should look at Option 2 below.
Approximate cost: £6000 installed
Same as above, but combined with a smart immersion tank. The addition of the tank gives you more power output, more flexibility of use and ultimately reduces your bills because you are almost guaranteed to charge only at night.
What else can you do?
The power required to heat the house ultimately depends on how well-insulated the building is and how efficient the heating system. It makes sense to address the building fabric and the heat engine simultaneously: improving the fabric reduces energy requirements, and the cheapest energy is the one you don’t use.
Fabric first: Old buildings (pre-war) have no cavity walls. Insulating walls from the inside can be tricky and expensive. Our advice is to advocate fabric improvements at the scale of the building to improve walls from the outside (where possible) and the roof. Instead, you can replace the windows and doors and improve air tightness by checking and insulating all the penetrations (pipes and ducts going out).