Sounds a bit high but then I don’ know your system by heart. I calculate 20 W per unit (streamer, pre, power) in idle. 24 x 365 it’s 525 kWh. I pay 0.3 euro per kWh, so 157 per year, 13 per month - in the Netflix league. Up to everyone to decide for themselves 
Putting the streamer into standby could reduce it. And worth remembering that most non-Naim power amps use much more in idle. Naims are class-B, so idle use is low. Not quite the same with A or even A/B. I had a Rotel using 50-60 W
As HH has said find a green energy supplier and cut electricity usage in other areas.
I use a green supplier to power my ASHPs so I’m not pushing CO² out of a flue. No matter how ‘efficient’ a gas boiler is it still converts carbon molecules to mainly CO².
I’ve got five Naim boxes (or six if you include the NAPSC) and they stay on!
I thought Naim were Class A/B ?
My 250 is warm on idle although this may be the regs 
You are right, they were B in the past apparently,
and, if that’s correct,
There isn’t much warmth, but Naim is not, and never has been, bright or edgy. Most Naim gear of old was strictly Class B. The Supernait 2, however, has a Class A preamp output stage joined to its Class B power amp section
(from the SN2 review in Wall of Sound)
but new ones are A/B, also says so on the Naim website.
But anyways, their idle power use is low for an amp
It all boils down to one’s priorities in life.
I have a friend who lives alone (no wife and kids) and always reminds us to switch OFF all the lights in our houses during “Earth Hour” in order to save the planet. This same person opines that he would only drive American SUVs with V8 engines.
Due to Covid, I no longer go out of town for work assignments or holiday. I just leave my boxes turned ON 24/7. I just turn them OFF during thunderstorms.
I guess this guy earns his living as a politician?
No, not a politician 
. He is just very passionate about these American gas guzzlers and he is not willing to “sacrifice” his driving experience with anything else.
Similar to us audiophiles / music lovers, we have certain “musts” that we don’t want to compromise, and that is sound quality. The level of compromises though vary from person to person.
To each his own.
This is an absurd thread. If I say what I really think Richard will get mad at me. The OP should do what ever he wants. If his shet blows up that’s his problem. If it sounds worse that’s his problem. Plenty of folks here who I believe know a lot about Naim have advised him. End of the story
Cripes!
Don’t take things so seriously, I mostly just visit this place for a chat about stereo’s, with all of the other weirdo’s. :0)
I hope I am allowed to support the OP’s approach even if this is the minority around here
not too complicated for me:
otherwise - service sooner is at hand, luckily. Imagine we had to make do without the great Naim service dept? Would you keep it all on for 10 years?
Naim amps, especially power amps, need probably about 20 mins max to warm up (if that), so switch it on, make a cuppa, relax and the music’s already there!
I also interpret the advice from Naim on this as OK to leave it on if you want it in constant peak performance 24/7 - it’s OK, not necessarily the best for the electronics? Could it be that it’s somehow become one of these amusing passionate folklore recommendations?
We have to take into consideration that no all people, even with costly equipment, value sound quality as the most important criteria.
Look at some threads where people prefer to use Chromcast with their Ndx2, or other who stack boxes into crap sounding cabinets because it looks better for them, or the OP here who prefers to sacrifice sound quality vs power consumption.
However I agree with Opus, perhaps a Naim forum is not the best place for them.
and the elitarian folklore continues! 
It’s his kit, he can do what he wishes with it. If he doesn’t like the sound it makes when he turns the amp on and off he can trade it - other makes are available.
I know. We , audiophile people, can be considered as animals from a Zoo.
I would not say “ elitarian” folklore but “ optimal utilitarian “ folklore.
Sure, but others can say that they think it’s not a good idea. Actually, after the first post it was necessary for someone to say it
Oi, who are you calling a weirdo, I resemble that remark!
Because he uses his power switch?
Do you have any idea how uninclusive this sounds. You make it sound like a cult.
Offer advice and opinions sure. It’s when people start talking to people in a way they wouldn’t if they were face to face that bothers me.
The OP is free to do what he wants with the amp but adding a cheap switch box with spring-loaded terminals that can’t accommodate NAC A4 let alone A5 is going to degrade it’s performance.
Imports from China don’t really contribute to lowering carbon emissions which I believe was the reason for the purchase of this device. 
The French know how to deal with the elite. Still thankful for that.