So I've been looking into this more and have been trying to work out two things: 1. Whether we can fit a hot water tank in the airing cupboard and 2. What it might cost per year to run (worst case).
The airing cupboard is 850mm x 650mm x >2000mm and currently houses our combi boiler. I know Octopus do a slimline tank, but they can be pretty strict on the 1m x 1m x 2m dimensions. I am not too concerned if they need to put other things in the loft, but as our loft already contains 165kg of batteries, I don't like the idea of any more heavy items up there so would not want the tank up there. We have electric showers and only use hot water for the sinks and the occasional very shallow bath for the kids, so we don't need a huge capacity tank.
You’ll need to talk to your surveyor about this. They can put the buffer in the loft no problem.
I wouldn’t skimp on the tank, make sure you get something that can also be used for showers. Trust me, mains pressure hot water blows an electric shower away and I’d fully recommend the upgrade when you next fancy doing some renovation work.
You could always get the structural calcs done for the loft and if it will go in there you gain a very useful cupboard in your house.
The location of the heat pump is also a consideration. The perfect spot would be against the wall on the other side of the house to where the boiler currently is. That would involve an approx. 8.7m run through the loft and then down and out around 4.8m to the heat pump if it were to be located there. The consumer unit is also on the other side of the house, so a cable run would be needed too (not to mention another sub-unit).
Should be fine, functionally there isn’t a limit, it just adds to the heat loss.
Cost wise to run, we use about 7200kWh of gas for heating and hot water per year. This is almost identical to what our EPC says (B 86) - approx. 7100kWh. We live in a 2019 new build which is extremely well insulated. Assuming the boiler is 95% efficient, that's 6840kWh of heat. Assuming a rough COP of 3.5, that's 1954kWh of electricity. We're on Intelligent Octopus Go EV tariff, so get 6 hours at 6p/kWh and the other 18 hours at 25.045p, so that would be an average 20.28p over the 24 hours. That would be £396 per year vs £454 for gas - we would only require a COP of 3.0 to break even. This is worst case and does not take into account that we have a 14.7kWh battery and 9.42kW of solar, so it would be substantially less in reality. We could eventually also go induction hob and remove the gas altogether, saving the £108 standing charge per year.
Your gas boiler definitely isn’t 95% efficient regardless is what the sticker says, however you’ll probably run the house slightly warmer on average than you otherwise would with the boiler because it will be cheaper per kWh to run.
But given you have solar, batteries and time of use, you’ll save some money either way. Gas can’t compete when you are paying below the going rate for electricity.
I also really rate induction hobs, they work very well but it does mean you can’t use cheap aluminium pans and the aluminium pans that claim to be induction compatible because they put a thin bit of steel on the bottom are not great either.
I did a test yesterday running the combi at 50C to see how the house temperature faired and it did struggle a little but did eventually get to temperature, so I imagine we'd need a few radiators replacing, but nothing drastic. The quote suggests Octopus will do this. We're on the standard plastic 10mm OD piping to the radiators so not ideal, but pretty standard for new builds.
I’d expect then to want to swap your reception rooms and bedrooms as a minimum.
I think for the quoted £600 installation cost it's worth it for us. The wife likes the idea of the house being a constant temperature so is in favour too. The big question mark is the hot water tank. I guess the only way to know is to have the survey.
Yup, pretty much.
See my comments about the tank above. I wouldn’t write off the loft either, the extra space in the house is more useful.
