Note: Every home and schedule is unique. What follows is generally true for most homes, but insulation levels and schedule preferences make a big difference. A key benefit of Havenwise is it learns exactly what is best for every home, every time.
Flat tariffs
If you're on a flat tariff, then the key is to run "low and slow". This means the lowest possible flow temperature, for the longest time.
This usually means only small setbacks in room temperature overnight, because it is more expensive to turn off for 7 hours then spend 1hr at a high flow temperature, than to keep running at a low flow temperature for 8hrs!
Why is this? A good rule-of-thumb is that for each 1C increase in flow temperature, CoP (and therefore cost) decreases by between 2 to 3%. So as little as a 10C increase in flow temperature can cost about 30% more to deliver!
This means almost all homes benefit from "banking" cheaply produced heat at low flow temperatures over long periods of time, even after considering heat loss to the outside.
Time-of-use tariffs
Everything changes with a time-of-use tariff. If energy is currently 4 times cheaper than normal, then your heat pump could operate 4 times less efficiently and still cost the same to run.
This means it is absolutely cost effective to run your heat pump, for example, 2 times less efficiently than normal during such a period. This is why our users on EV tariffs see Havenwise ramp up so much overnight on mode 1 - it is "banking" the cheap heat! This of course isn't for everyone who can't prevent the heat going to bedrooms overnight, which is why we offer mode 2 to disable this, or setting lower schedules overnight.
But where is the sweet spot for less dramatic swings in energy price? This is where Havenwise shines most - it dynamically calculates the absolute cheapest action that will maintain your comfort.