If youre already on a smart tarriff, it is apparently, very difficult to switch from that,to a day/night meter, but some have managed to do it.
For the heat pump, you can set a timer on this, to only heat the water during the night rate hours, typically most people with this setup, have the water heated, before morning showers. You can also limit the upper temperature, we use 50 degrees C, and this has worked out fine. Its pointless, heating water to a temperature above that, if it is not being used. The only time we’ve been caught out is where we have say 2 friends staying, and extra showers etc. you can manually over-ride where required, we don’t have any electric showers.
For house heating, find a temperature that suits yee, and set that. This depends on personal preference, and the insulation level and BER of the house. It tends to come on occasionally to maintain temperature's at night, and more frequently on cold winter nights.
During cold nights, the heat pump automatically comes on and goes into “antifreeze” mode, this uses bare minimum power, and significantly less, than when it is actually heating the house, i could be wrong but my understanding is, this is just keeping the external unit, above a minimum temperture.
To benefit fully, from a day/night meter, you also need to change some habits, and time washing machines/dryers/dishwashers, to finish before the night rate ends. We also changed appliances over time, to efficient rated ones, and all bulbs changed to low wattage LED’s, and get better at switching off things, rather than leave them on standby, cumulatively, these items, all add up.
50% usage on night rate is relatively easily achievable. We have an EV also, so its higher, but expect it to go to more than 60 % this summer, as the heating not in use, as tempertures rise.
If you actively make some habit changes, a day/night meter is difficult to beat, i’ve run the numbers a number of times, and makes sense for us, but is largely dependant on each individual household setup. The higher annual standing charge is more than compensated for ourselves, assuming you can move 50 % + to night rate.
The 9 hours on a much cheaper rate, means it is the most practical setup, by far, for an EV, as you are not plugging in/out every single night to avail of a 2 to 3 hour low rate, which is what is only on offer on smart rate plans.
Solar PV, is also an option to consider as well, we don’t have this currently, allthough i have got a quote last year, and thought the payback was a little too long, but keeping an eye on this also.