TL;DR: I'm currently in a fight with my heat pump, as its energy consumption seems way out of line. I want to know what it is doing, that is causing it to use so much electricity even when the outside unit isn't doing any heating at all.

System: Alpha Innotec LWD 50A/SX HTD-S. It's a combination of an outside unit that does the actual heating, and an inside unit, where the inside part also contains a large buffer vessel for hot water and a Luxtronik 2.0 control panel. It uses R290 as a coolant. I'm not exactly sure when it was installed (the apartment was newly built) but it's been in use since September 2021. The heating of the apartment is done with underfloor heating with hydronic elements.

It is combined with an Alpha Innotec RBE+ thermostat, which has a touch screen that is 'always on'.

The heat pump has several settings for heat/hot water, two of which are relevant: 'off', and 'automatic', the latter meaning you can set scheduled times, so e.g. it won't start heating up hot water in the middle of the night after an evening shower, or turn on the 'night' mode for the heating. Night mode for the heating means it will lower the "heating curve" by 3 degrees Celsius. Currently, I've scheduled day mode from 8 AM to 8 PM, and night mode from 8 PM to 8 AM the next day.

Monitoring: I'm currently monitoring my energy usage using a site/app called 'mijnenergiebundel' which came with the apartment. This software splits my energy usage into two categories: 'building related', which only reports any electricity usage when the outside unit of the heat pump is working, and 'domestic', which reports everything else, including the electricity usage of the inside unit, like the Luxtronik and RBE+.

I can also monitor when the outside unit of the heat pump turned off after being used, as the Luxtronik allows me to see the last five 'afschakelingen' (shut downs).

Now, as long as I have the heating set to 'off', my energy usage looks something like this, a pretty constant usage of 0.05/0.06 kWh (the spike at 8 AM was me). Cutting all power to the inside unit of the heat pump makes this go down by 0.01/0.02 kWh, I'm guessing that's because the Luxtronik and RBE+ are 'always on' and cutting power means they're off too.

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As soon as I put the heating to 'automatic' though, my energy usage looks much more erratic, like this - the highest peak there is 0.12 kWh, the two lowest at the end were immediately after the hot water was heated up, and are 'normal' at 0.05 kWh. This was an office day, so with the exception of 15-20 minutes of lamplight to get up in the morning, there was no other energy usage. I checked when I came home, and I did also not forget to turn off the Wi-Fi, leave a light on, or the fridge door open. The outside unit didn't turn on except for one time around 1 PM to heat up the hot water buffer.

Enter image description here

So, on average, with the heating turned to 'automatic', the inside unit of my heat pump seems to be using 0.04 kWh extra each hour, so about 350 kWh a year. I'd really like to cut all that out, because with current energy prices that means about 200 euros I can save each year.

What could the inside unit of my heat pump have been doing that made it use so much electricity, so erratically? Is there anything I can do to make it behave, and go back to having just 0.05/0.06 kWh of standby consumption, while having the heating set to the 'automatic' schedule?

  • 2
    When the system is off, it uses no energy because it's not heating anything. When it's set to auto, it uses energy because it's maintaining a temperature. Why is this not what you expect?
    – longneck
    Nov 14, 2022 at 14:28
  • @longneck because I'm expecting it's the outside unit that is getting heat to maintain that temperature from the outside air, yet that unit is not on, not using any energy. This is the inside part of the system which is using energy. That part of the system has no way to heat anything up as far as I know. Nov 14, 2022 at 14:59
  • 1
    Don't trust any statistics that you haven't faked yourself. I have seen lots of broken energy monitor equipment, especially in the last few years as everyone seems to install the cheapest thing they can get. Many are inaccurate below some 10s of watts, some are not even able to properly distinguish between Wh and VAh, some take measurements every minute and interpolate the last minute from within that, or even for longer periods. If you are really intrested, setup some mesurements yourself and tinker with the controls.
    – PlasmaHH
    Nov 14, 2022 at 19:46
  • 1
    @PlasmaHH Well the data I've been getting has been constant enough, and I have been able to verify turning on e.g. a 40W ventilator overnight also accurately adds 0.04kWh to the measurements for that night. The monitoring gear doesn't seem cheap, though I don't know for sure. There are kWh meters mounted directly into the fuse box and those are being read by a device labelled "EMX" Nov 14, 2022 at 20:09
  • 1
    @Harper-ReinstateMonica 0.04kWh * 24 hours a day * 365 days a year = 350kWh. Prices here are currently at 0,73 eurocents per kWh, making this close to 200 euros. Nov 15, 2022 at 7:06

2 Answers 2


The heating of the apartment is done with underfloor heating with hydronic elements.

Then you have a circulation pump. That probably explains the "high" standby power use, as 50 W is otherwise excessive for what is a modern high efficiency unit.

I skimmed the manual for your unit and it says the pump must be controlled by the unit and never shut off externally. However, the manual suggests the duty cycle of the pump can be configured. The default is listed as 5 minutes on / 5 minutes off. From what I understand, you can go all the way to 1 minute on / 120 minutes off.

I haven't read through the whole thing and it's not clear, locally, if this setting applies only when heat is required or all the time. I suggest you give the manual a proper read first. If the setting is indeed all the time, you probably won't want to turn this too low or your heating will not work correctly. But you seem to have a good grasp on experimentation and taking measurements, so I think you can figure out what's optimal for your use.

  • I think I've found the setting you're talking about before, but this is for circulating hot tap water (so you don't have to run the hot water for long to get some from the tap), as far as I know it's not a setting for the circulation pump for the floor heating. Circulation pump was a thought here too, but the erratic nature of the power usage made me think it was highly unlikely. As a pump that's continually running should have a much less erratic pattern to it, I thought. Nov 14, 2022 at 16:32
  • That setting is already at 1/120 too, as I live in a small apartment and really don't need the tapwater circulation. All it does is make sure the hot water cools faster. What manual did you find? Maybe yours is more informative than the ones I found.. Nov 14, 2022 at 16:37
  • 1
    @Tinkeringbell French manual from this page, under the "Fichiers" tab, 3rd and 4th files. None came up in English but they probably exist somewhere. You may be right about that setting but you must have a pump for your floor heating too. There are references in the manual to a "glycol water circulation pump" and economy settings for it but I'm not even sure if they're talking about an inside loop or an outside loop. The manual is very terse, even at 90 pages long.
    – Olivier
    Nov 14, 2022 at 18:47
  • 1
    Yeah, I have looked at the same manuals just in Dutch then, from the .nl version of that site. That setting really was for tap water. I'm still finding the erratic usage weird (like, why would the floor heating circulation pump some hours seemingly require 0.08kWh, and others just 0.01 or even none?), but I'll go trawl through those docs again to see if they have an answer to that. There is another circulation pump setting that I'm not allowed to change, but it's a single setting (no on/off like with the tap water) set at 60 seconds. Nov 14, 2022 at 19:59

As soon as I put the heating to 'automatic' though, my energy usage looks much more erratic, like this...

When the thermostat is set to 'automatic', it's pumping water through the floors as necessary to maintain temperature in the apartment. Why wouldn't you expect some sort of electricity usage for that? The "as necessary" portion is why the usage seems "erratic". This is the way all heating systems work.

If we were to presume that your lower graph were based only on heating use, then it still makes sense and doesn't seem all that erratic to me. It takes more to heat the apartment overnight because it's colder outside. Therefore (no matter how much insulation) there is a greater thermal difference between outside & inside and more heat is lost to the outside, requiring more heat to be produced inside.

During the day, usage may vary as the outside temperature varies, and even as cloud cover changes because it makes the air temp change.

If you really want to eliminate this usage, then you'll need to set the thermostat to 'off' and deal with the fact that your apartment will be cooler when you turn it back on than it was when you turned it 'off'.

  • I'm willing to believe you (and the other answer), but I can't wrap my head around it still. So, just to be clear: It will heat up the water it's pumping through the floors once, then keep pumping that around as necessary/erratically to maintain a temperature? Even when the water has given off it's heat to the floor/air in my apartment, and thus has cooled down, it doesn't need the outside unit to warm the water up it's circulating up again? Nov 15, 2022 at 15:53
  • And what is it 'maintaining' because the temperature I want at night should be 3 degrees lower than during the day, so 19 during the day and 16 at night. Yet so far, if I turn it to 'off', it's never been below 18 in the morning yet. Why isn't it letting the apartment cool down to 16 degrees before trying to 'maintain' that then? Nov 15, 2022 at 15:54
  • It's unclear to me whether your "Automatic" graph includes having the outside unit on or off, but I'd presume that if the inside unit is on, the outside unit is on, too. If the outside unit is off, not heating water, then the inside unit will still circulate water in an attempt to heat. Only it has to run even more because it's trying to heat with cooler & cooler water each time it runs. If it does this long enough, eventually, it will run cool water through the floor, absorbing heat from the room and pumping it outside the house.
    – FreeMan
    Nov 15, 2022 at 16:00
  • All heating comes with a "dead zone" that prevents the system from constantly cycling. It will allow the air temp to drop to a couple of degrees below the set point, then heat to a couple of degrees above the set point and turn off again. This helps prolong the life of the equipment. It may be that your place is well enough insulated that the temp drop isn't enough to completely cool the water, and that the circulation pump is able to keep the inside temp warm enough with the outside unit off...
    – FreeMan
    Nov 15, 2022 at 16:02
  • 1
    This place is mostly brand new and really well insulated, so the theory of it circulating water again and again without needing to heat the water up again could make sense. I'll go see if I can find anyone in real life to take a look at the thermostat, because I still think it shouldn't be circulating at all then, if the temperature is at 18 when all I ask for is 16? Nov 15, 2022 at 16:29

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