Heat Pump Running Costs

i have the same, all i can get is power usage via a shelly EM, there is some way of getting more info but not as straightforward as other systems.

I know i have my DHW timed over night so generally can ID what heating and whats DHW. (DHW tends to use circa 2.25KWH)

Hi,

Like you, I have 12 heating zones. In theory, that’s great, as you are only heating the rooms you need.

However, what actually happens (and I am assuming you have MHRV) is that if one room calls for heat, the laws of thermodynamics (and common sense!) mean the heat in that room will naturally flow into the colder rooms. In effect, that one room is trying to heat the entire house and will probably struggle to reach its set point. Added to this, a heat pump works best with larger volumes of water at lower temperatures. Heating a small loop results in the return temperature not being low enough, so the heat pump ends up cycling on and off and working very inefficiently.

My theory, which I think I've proven correct, is that it's better to heat the entire house as a single unit. Your MHRV already treats your house as one sealed unit and moves heat around, so you should heat it that way as well. During the winter, I stagger the upstairs and downstairs by an hour, so the downstairs comes on an hour earlier. I also have more realistic temperature settings in the evening (though still high enough for most zones to come on), so particularly warm rooms will switch off. But at night, around 3 am its balls-to-wall, I have all zones set to 23°C. At 6 cents per kWh, this costs next to nothing—maybe 20-30 cents a night (50 cents at most).

This strategy works for over 95% of the winter. On the really cold, miserable, windy days, I just let the system do its thing and allow each room to call for heat whenever it needs to. Because it's extra cold on those days, a lot of loops will be open anyway, so the system will be working as efficiently as possible.

My experiment started as a cost-saving exercise (to max out the EV rate at night) but ended up achieving both: I saved 33% on cost and reduced my actual kWh consumption by 25%. I reckon I could do more if I had a bit more control and could predict solar gain for the following day, but that’s another project.

Regarding comfort, I’ve had no complaints from the family. The entire house is a nice, even temperature. Yes, one or two rooms might be a degree colder, but it's nothing drastic.

If this is your first winter with the heat pump, I would say let it do its thing and learn how it works. The last thing you want is an earache from the family while you're experimenting with the heating! But maybe in a month or two, try this strategy for a week and see how it works for you. Also, keep a close eye on your consumption by checking it daily. Have you a live energy meter on your heat pump to see exactly when it's coming on; this is important for understanding what's happening.

October 2025

114.4kwh heating

53.3kwh hot water

Almost all night rate @13c (with the exception of of some of the hot water)

October 2024 was same hot water but 96kwh heating.

Agreed, its what the app says though.

Only 2 people in the house currently.

The house is 215sq metres.

ours is 192 sq/m but with 4 people in it (just as a point of reference) probably some optimising to be done :)

It is on 24/7 although mild enough at the minute, set at a temp of of mostly 20°. Taking yesterday e.g. the heat pump ran for just over 6 hours.

I meant from a cost point of view it will all be at the EV rate as the battery (charged at the EV rate) will cover all our electricity needs throughout the remainder of the day.

Heating schedule is:-

18° 22:00-04:00

22° 04:00-06:00

20° 06:00-22:00

Hot water set for 02:00-06:00 (it probably takes 1.5-2hrs to heat the water)

Yes correct running a Viessmann unit.

Unsure about what the heat curve is set at.

Its only a new build so tying feel my way with it without making too many changes at once.

What is the best to do next:

1- The 4 bedrooms are on rooms stats and actuators. Currently set at 19.5. Remove these, the house will be fully open loop then and allow the master stat to control the entire house?

Or

2. Reduce the heat curve?

Bedrooms can still be cooler in an open loop system by adjusting flowrates to them rooms at the manifold.

Yes a bungalow.

Like newhouse87 said, I might need to reduce the flow rates.

Thanks for that and a good explanation. I will look at the heat curve after tinkering with the bedrooms

Nov 477kwh, cost €115. Radiators, 180sqm, 21 downstairs and 18 upstairs (temps) above average insulation etc. Have accepted that it won't use less kWh having tried various adjustments over the last 2 years.