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Rank 2
September 5, 2025
Solved

New build. Daikin heat pump Altherma 4 advice please.

  • September 5, 2025
  • 15 replies
  • 1034 views

I have recently moved into a new build house with a heat pump system.

 

Its a Daikin Altherma 4 with a 280 litre cylinder.

 

The hot water is currently set to 45c on a reheat setting.

 

I'm trying to make it as energy efficient as possible on the hot water side.

 

I keep hearing so many different reports on which setting is best etc.

 

We are a family of 4. 2 adults and 2 teens.

 

We all normally shower etc in the evening and wash the dishes mainly in the evening, all of which happens roughly around 6pm to 8pm.

 

I'm up at 6am for work and have a quick face wash etc around 6.30.

 

The weekend is similar but sometimes the showers, baths happen during the day.

 

 I have heard that Schedule and reheat is better than just reheat?

 

If so, what kind of times should i be setting on and off, and what temps?

 

Also is it better to have a longer set back temp. like 20 or 25c or just leave it currently at 10c?

 

Also is eco better than comfort?

 

At the moment, we find that 45c on reheat works fine, but i would like to get the hot water schedule as efficient  as i can.

 

Any advice would be greatly appreciated.

 

Best answer by juliamc

There are 3 settings you can choose between: Schedule; Schedule and Reheat; Reheat (only). 

I have mine set to Schedule and Reheat, which I think is the best of both worlds. 

I think you should try setting yours to Schedule and Reheat. You could have the Comfort temperature at 48 and Eco at 45, then set the schedule to Comfort at 3pm and Eco at 3am. You will want to have the room heating on soon so you need to heat the water when you won’t notice the heating is paused. Lower your reheat temperature to 40 deg so it doesn’t reheat too often.


Nb. When it’s running the Schedule the hot water heating cycle will start at the set time, and heat the tank until it reaches the target temperature. At that point it won’t heat the water again until the next scheduled time. You don’t actually need to set a Stop time.

The other thing about timing all this is that 4pm to 7pm is the peak time for electricity usage. If you can avoid heavy use during those hours you will be helping the grid. There are some tariffs that offer a cheaper rate outside of those hours.

15 replies

BPLightlog
Super User
Super User
September 5, 2025

Hi ​@Aloha , ours isn’t a new build but we did have a Daikin ASHP fittted earlier this year.

 

What I’ve noticed with all the various notes from people is that each property and family needs are different so don’t be surprised if you end up with some adjustments just for you.

 

We have a slightly smaller hot water tank and ours is heated to 47 degrees C early morning, ready for showers (4 adults). Our water remains hot enough for most other usage during the day but we have another heating time mid afternoon which tops up to 40 degrees if needed (no reheat, just two scheduled slots).

 

The eco and comfort settings are simply preset temperature levels so that you can easily choose which you need and when.

 

You can set different timings for each day and so you might find that your weekends are rather different to weekdays.

 

For heating, we only setback to 19 degrees overnight so that the heat pump doesn’t need to work overtime in the morning to get the fabric of the property back up to temperature.

 

Of course, one other thing to consider is your tariff. Our tariff gives lower cost electricity early morning, early afternoon and late evening so your prime usage times of 6 to 8 pm might mean that you need to prepare before and avoid reheat during that time as it can be charged at peak rates.

 

I'm sure you’ll find your ideal set up after trying a few things before too long.

 

There are several who use the forum who have had their heat pump longer than I have so they may be able to comment as well.

Bring me Sunshine ~ E&E {Solar PV, Battery Storage, Hybrid EV, ASHP and Home Assistant automation}
AlohaAuthor
Rank 2
September 5, 2025

Thank you for your help.

we mainly all have our showers etc after 7pm so ours would kind of be opposite to your settings.

so if I put a setting of say on at 6am, can I then set it to off at 7am? Donut won’t come on even if the tank goes cold? 
im just trying to work the best way to do it so I don’t have reheat on 24/7

BPLightlog
Super User
Super User
September 5, 2025

Thank you for your help.

we mainly all have our showers etc after 7pm so ours would kind of be opposite to your settings.

Yes, I presumed that from your post 

so if I put a setting of say on at 6am, can I then set it to off at 7am? Donut won’t come on even if the tank goes cold? 
im just trying to work the best way to do it so I don’t have reheat on 24/7

This is my hot water schedule for today .. 

Your time slots would be different but you can set a time for heating and a time off (not heating). Our second slot in the afternoon uses the eco level so only heats if the temperature has fallen below that level … a sort of ‘controlled’ re-heat.

Bring me Sunshine ~ E&E {Solar PV, Battery Storage, Hybrid EV, ASHP and Home Assistant automation}
juliamc
Rank 20
Rank 20
September 5, 2025

@Aloha a couple of questions: what tariff are you on and do you have solar panels?

I've read that heating the tank from cold is the most efficient as far as the heat pump is concerned (discussion on OpenEnergyMonitor forum). So if you’re happy to do a bit of experimenting you could set it to a schedule to heat up during the day, particularly if no one is at home. That would mean the outside temperature should be warmer and the hp has less work to do. You could raise your target temperature a bit, eg 48 deg, and see if it lasts the evening.
You mentioned set back, which is usually a term for lowering the overnight room heating target temperature. Did you mean the Reheat Hysteresis ? That is 10 deg by default, so if your reheat temp is 45 the hp will operate when the tank temperature goes below 45-10 ie 35 deg.

You could keep those values and set the system to “schedule and reheat” then see if the reheat kicks in after all those showers. My reheat starts if I have a long shower for a hair wash. However the reheat is set at 40 deg. 
It’s all trial and error to see what works best for your household. Good luck !!

juliamc
Rank 20
Rank 20
September 5, 2025

One more thing to consider once room heating is needed: the heat pump cannot do both hot water and room heating at the same time. 

BPLightlog
Super User
Super User
September 5, 2025


You mentioned set back, which is usually a term for lowering the overnight room heating target temperature. Did you mean the Reheat Hysteresis ? That is 10 deg by default, so if your reheat temp is 45 the hp will operate when the tank temperature goes below 45-10 ie 35 deg.

Ah yes - I hadn’t considered the hysteresis level on hot water as I don’t use reheat 😬

Bring me Sunshine ~ E&E {Solar PV, Battery Storage, Hybrid EV, ASHP and Home Assistant automation}
AlohaAuthor
Rank 2
September 5, 2025

@Aloha a couple of questions: what tariff are you on and do you have solar panels?

I've read that heating the tank from cold is the most efficient as far as the heat pump is concerned (discussion on OpenEnergyMonitor forum). So if you’re happy to do a bit of experimenting you could set it to a schedule to heat up during the day, particularly if no one is at home. That would mean the outside temperature should be warmer and the hp has less work to do. You could raise your target temperature a bit, eg 48 deg, and see if it lasts the evening.
You mentioned set back, which is usually a term for lowering the overnight room heating target temperature. Did you mean the Reheat Hysteresis ? That is 10 deg by default, so if your reheat temp is 45 the hp will operate when the tank temperature goes below 45-10 ie 35 deg.

You could keep those values and set the system to “schedule and reheat” then see if the reheat kicks in after all those showers. My reheat starts if I have a long shower for a hair wash. However the reheat is set at 40 deg. 
It’s all trial and error to see what works best for your household. Good luck !!

Thank you. Yes that’s what I meant.  I didn’t know how to spell it haha. 
thank you for you great advice 

juliamc
Rank 20
Rank 20
September 5, 2025

Nor did I but thankfully the phone did !!

AlohaAuthor
Rank 2
September 5, 2025

So without sound too silly.

if I set it to come on at 5pm till 8pm at 45c on schedule and reheat, then off all night till 6am the next day till 8am at 45c it would be more efficient than reheat only at 45c ? 
as a family we tend to have showers etc in the evening after 7 ish.

just trying to find if it’s better for me to do that schedule or leave it as it is at 46c reheat. 
we have a fixed rate tariff currently, so it doesn’t matter what time of day 
 

juliamc
Rank 20
juliamcSolved
Rank 20
September 5, 2025

There are 3 settings you can choose between: Schedule; Schedule and Reheat; Reheat (only). 

I have mine set to Schedule and Reheat, which I think is the best of both worlds. 

I think you should try setting yours to Schedule and Reheat. You could have the Comfort temperature at 48 and Eco at 45, then set the schedule to Comfort at 3pm and Eco at 3am. You will want to have the room heating on soon so you need to heat the water when you won’t notice the heating is paused. Lower your reheat temperature to 40 deg so it doesn’t reheat too often.


Nb. When it’s running the Schedule the hot water heating cycle will start at the set time, and heat the tank until it reaches the target temperature. At that point it won’t heat the water again until the next scheduled time. You don’t actually need to set a Stop time.

The other thing about timing all this is that 4pm to 7pm is the peak time for electricity usage. If you can avoid heavy use during those hours you will be helping the grid. There are some tariffs that offer a cheaper rate outside of those hours.