Improve efficiency: holiday mode?

How long do you need to be away for it to be worth putting the heat pump into holiday mode?

And do you regard this as “turning it off”? I do, as the button on the Mitsu FTC has a power symbol as well as a suitcase on it, plus the pump almost never runs in that mode (only late in the coldest nights). I think most people would call that “off” rather than reserving the term only for use of the Big Red Switch outdoors.

For completeness, someone on Facebook was advising not turning a heat pump off over xmas if away for less than two weeks, vaguely citing unknown comments from heat geeks and @TrystanLea as the reason. I suspect a misunderstanding, but it could be mine!

On the FTC you can set the min room temperature to be maintained so if you set this high enough you can treat Holiday Mode as a long set back period.
You can also set the min water temperature which I assume is to reduce the risk of freezing pipes outside.

Note that the end date is the last day you are away not the day you get back as I assumed.

You can see what my Ecodan did while in holiday mode here Emoncms - app view

I turned it on around 18:00 on 26/12/2023 with the end date set to the 31st as we got back on the morning of the 1st.

One thing to note is that our FTC6 main controller is in the hallway where there currently is no radiator and all the internal doors would have been shut so when room temperature was dropping to 16 degrees it was probably warming all the rooms with radiators quite high before the FTC would have seen the temperature rise.

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Oh, I’ve just had a thought, do you have an FTC5 or FTC6 (I vaguely remember you might have a 5)?
I think the holiday mode might be one of the differenced between the two.

Yes, a 5, but it sounds like yours. It may differ in some small details. For example, holiday mode on mine can’t be shut off early by the melcloud app.

How long are you away before you use holiday mode? I think it worth using for two day absences.

I turned ours off while we went away for 10 days over Christmas. Then started to warm the house 2 days prior to coming home which seemed to work well.

Only issue we had was our BUH (Daikin) was turned off, unfortunately, the unit needed this to be on as it had been off for a period of time. Luckily I could guide my dad on how to turn it back on before coming back.

I think in the future I’d be a bit more aggressive with a higher set back temp. This is pending a change in controls to the Madoka as we have Tado at the moment which I don’t trust!

I’d guess that it depends on how well the house keeps its heat vs. how long it takes to get warm again. Some houses (e.g. stone walls / high thermal mass) will take longer to recover, so it’s worth keeping them warm for short vacancies.

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We turn ours off even if we’re just away for a day. It only takes and hour or two to get sensibly warm again. We’re usually charging about unpacking when we get back so that activity keeps us warm. Oh, and a cup of tea of course.

We went away for three days last week and left it on just to see what happened. It felt weird and used plenty of electricity that it didn’t need to.

How much extra electricity would it have taken to warm the whole house up again? I guess that depends how cold it gets when not heated…

Our house got to be about 10.5 degrees whilst we were away. I would have set our house to 16 but I don’t trust Tado!

It seems to work better when you set it to be “on” - not maintain x temperature.

With the tweaks we made to the Daikin, it was essentially running in LWT until we got back.

In the 3 days we were away last week it consumed 45 kWh energy.

(you can see why I like to separate DHW and space heating on the other heat pump app for investigations like this, the space heating was actually 38 kWh)

Even with the heating on it still got cooler because the humans weren’t around doing things:

We lose about 1 degree per 10 hours when not heating:

That period of no-heating wasn’t long enough to allow me to look at recovery, it didn’t get cold enough to create a statistically significant recovery event.

Here’s a better example from January 2023.

Heating was off 2023-01-14T15:20/2023-01-16T12:40. It was cold outside and got colder. Let’s just be clear, any sort of holiday mode would be set to protect the house from getting cold enough to cause damage.

Room temperature went from 22.3 to 15.8 = 6.5 degrees over 45 hours => minus one degree per 7 hours. It heated back up over 9 hours from 15.8 to 20.3 = 4.5 degrees => plus one degree per 2 hours.

Zooming in on the recovery:

That was 24 kWh to come back.

I’m using the time from “off” to “recovered” to compare to another time. That’s about 54 hours.

I’ve hunted around for an equally cold time and found December 2022. In that same time window, with similar outdoor temps the heat pump used 80 kWh for space heating. In this specific case that’s three times as much energy than was be used for recovery.

Given this, you’d conclude that:

  • You use more energy to heat the house whilst you are away than you use in recovery
  • You should invoke the recovery before you get back home if you want it warm

Clearly there are many variables at play here. The outdoor temperature in this case meant there was a significant recovery event. Normally we don’t even have a noticeable recovery because the temperature drop isn’t very much.

You’re all quite capable of working out the formula for determining the heat loss over a period of time (thanks Newton) paying particular attention to the fact that heat loss gets much smaller when the house cools closer to the outdoor temperature. As a result, longer “off” times don’t get a lot worse than shorter ones. You can see here that it’s not a straight line down, and in fact towards the end it even plateaus:

The plateau in the middle is where it was daytime for a few hours and got warm outside which shows that heat loss is affected by outdoor temperature as you’re all well aware. In my case the house barely cools when it’s 10 °C outside:

If you want another way to look at it, these delta events show when the temp dropped and you can see they get more spread out as it stops dropping so often:

As the original question implies, the longer duration holidays clearly make sense as times to put the heat pump into holiday mode.

For shorter duration events it also makes sense. When we were on a different electricity tariff we even switched off overnight which is a very short holiday :slight_smile:

My personal conclusion is that it’s always more cost effective to turn off the heat pump when you don’t need it, the duration doesn’t matter.

In Andrew’s case it looks like it was about 20 hours to recover so I can see why people might conclude that you should leave it on. That was 34 kWh for recovery and the holiday time window would have used 76 kWh if it was left running. The recovery was cheaper than leaving it on. This is glossing over things like time-of-use pricing that might mean you’d bump it on even when you aren’t there because the cost is so low.

For some situations your question might revolve around a more intense reactive recovery at higher flow temps (and hence lower CoP) rather than pro-active recovery. The old-fashioned “whack the thermostat up when we get home” trick that we know is somewhat misguided even with fossil-fuelled systems.

Practically our problem has always been knowing when we would return. Most of our holidays are somewhat open-ended so we’re never quite sure when we’re getting back. Even with more structured holidays we’ve had travel delays of over a day. There comes a point where you just have to accept that to get guaranteed user comfort you are going to need to accept some inefficiency.


FYI: Click on “Space heating” COP to see stats breakdown for just the heating. Same for “Water heating”.

Yep, that worked as expected, thanks Tim.

The recovery time is an isteresting point. I suspect people on here have carefully tuned set ups balancing the supply to the loss. But as a result these are going to be the systems with some of the slowest recovery times.

On our vaillant i have wished for a boost option that puts up the flow temp for an hour if the house is not heating up fast enough. A loss of efficency but only for a short period.

I have taken to raising the target temp by a degree and this shifts the weather curve up quite a bit for faster recovery. Then put it back down for better long term efficiency.


That’s a good approach Joe.

It’s the sort of thing we want the vendors to bake into their control algorithms so we want to show how they work and what our experiences are.

Ive added a holiday mode to my ‘Agile optimiser’ - it just shifts the set points down for the specified period, but makes the set point in the high priced periods even lower so that it won’t ever run in those slots.


My property loses 0.7° per hour, so would get rather cold over 10 hours. Heat loss coefficient is 260 W/K, despite having cavity wall insulation and double glazing. I suspect there’s many more drafts I need to find and seal.

  • Chart of house temperature (blue) and rate of change (yellow).

As I’m on the old RHI grant thingy, I’m paid according to how much renewable heat is measured from the heat pump. This is usually more than it costs to run it, so it’s economically beneficial for me to keep the heating on while we’re away.