What are we talking about here.?
I assumed it was a sump heater or a diesel tank heater but from your description it seems to heat the car interior.
Note even sure if you have a ‘collection’ of heaters (sump, interior, windscreen) not even sure if your car is garaged or is ‘on the street’
Are the figures you gave ‘as recommended by the manufacturer’ ?
If you need something different and you are happy with a) a linear response b) an intersect at 180 minutes (ie max duration even if at - 50 °C) then what duration do you need at (say) - 2° ?
It makes sense that it takes longer close to zero, not just because the specific heat capacity of water is huge, but because the phase change of water is even ‘huger’ (not a real word).
If (say) you wanted 40mins at - 2 then the formula would be 140-(-20*temp) I think, I’m doing it in my head again.
I use both car engine heater (typical solution here that radiates heat near the engine and warms up the oil) AND another heater that blows out warm air inside the car, that eventually removes ice from windscreen (and it’s comfortable as well 
). They both trigger from the same power plug. Both cars are outside “on the street” so to speak. The figures I gave are not recommended by some specific manufacturer, but I have got them from various sources around internet, unfortunately I don’t have an english links for you, just in Finnish. Anyway, here’s some info as for why to pre-heat a car in the first place for people who don’t know
I think that would be perfect. As it’s also said that there is no point pre-heating your car MORE than three hours in a row, and 40 mins at -2 is probably just okay as well. And it doesn’t matter if the formula would mean that there would be some heating minutes even in +5C, because the condition in that automation only triggers if temperature is less than 2C
Okay, so now I’m curious.
I assume your ‘switch’ is inside your house.
And there’s an adapter strip inside the car to feed the various elements.
The engine heater is probably built in (dealership fitted option ?) but that has a plug to go into the adapter ??? And you move the interior heater from (boot/trunk/back seat) to go on a front seat ?
So does the cable to the car have to be armoured ? Or is it ELV ? (extra low voltage, normally < 55v)
I’m just imagining the litigation issues from people being electrocuted 
How do you get the cable into the car? Just through the door seal will deform the seal and damage overall ‘weather integrity’
Why is your wife’s car not on the same ‘switch’ as yours ?, or is that to allow you to set different departure times ?
Wow, it’s a long saga…
Well, my wife and I have different time tables so both have their own departure times, not to mention that my car is on the front yard and my wife keeps hers at the back yard. Basically first we need this:
That goes to normal electric outlet (and there I have Sonoff), the other end goes to DEFA heater system that is installed in car. That is usually done in car repair shops and basically everyone in Finland has one in their cars. After installation, you have a plug in your car’s bumper where you plug in that green cable, and you have also an electric outlet inside your car, usually on passenger’s side, and there you can install this one:
Works perfectly, assuming you have remembered to plug that green cable in, but that is pretty automatic for us during wintertime 
Result: Your car starts flawlessly even if it’s -20C, AND it’s warm inside AND your car windows are cleared
I read your links and the ‘4 reasons’ one you posted earlier (I skipped it the first time)
I’m a convert !
These systems should be mandatory across northern Europe
(you will still get some idiot Brit who hasn’t read the docs and insists that it’s ‘meddling’ but to be honest they are scorned by anyone from the UK with more than 5 brain cells)
I do think they should be ELV though as some only have street parking.
Having said ALL that we should all be giving up combustion engines soon anyway, but the issue will just migrate to charging (heating will still apply too though, windscreens, interior and cell warming)
Hmmm, we live in interesting times (old Chinese curse) 
Well, these things are not mandatory here either, but it’s pretty darn good to have if you don’t have warm garage for your car, as it get’s old pretty soon if you have to scratch the ice from the windshield every damned morning when you are already late from work! 
As for those who have street parking, I think many of those have some sort of Webasto system instead. Or, they just have to scrape those windshields and punish their car engines…
And hence their wallets and the environment ! 
Living where it snows seems like far too much of a hassle 
I think you’d be better off migrating 
just give it ~5 years and it’ll be snowing less
Happy Aniversary !
Depends where you live, given the temperature change gradient and the increase towards the poles, the reduced polar salinity could turn off the gulf stream in the North Atlantic, plunging most of northern Europe into an other ice age.
Still, it might rain less !
I was just going to say that Scandinavia especially is affected IF gulf stream stops, so the climate warming will turn this part of the world actually colder! 
And that’s how discussion about home automation turned into climate change discussion 
Yeah. The point is we don’t know what the changes will pan out to. But all the models show there will be changes. I have no doubt that humanity will survive such, but how many other animals will not?
The environment is certainly more stable with diversity.
“But who cares about tomorrow when we can burn fossil fuels today and introduct more plastics into the environment which when not directly killing other animals break down into ‘pseudo’ hormones reducing fertility”
Still the world could do with a LOT less humans, especially the stupid ones (note: stupid <> less intelligent) - rant over !
But look what happened when we addressed flouro carbons ?
Bumping this thread as it seems to be the best automation yet with regards to car engine pre-heating, there are some other attempts that rely on packages, but the solution presented by Mutt was a beauty 
Opening this again is done due to two questions:
- I don’t know if the upgrades and changes HA wrt logging has changed since last winter, but I found that the time trigger of the automation a bit “noisy” in the logbook, is there any other means of sileincing it apart from adding a logbook exclusion in configuration.yaml?
- is there any way to pull the calculated times, “heatrqtm” (heat requested time?) and/or “mins” out of the service template for posting on a Lovelace card? The “huge number” mentioned, that would be in Epoch-type of time I presume.