This thread seems to waiver a bit between heating an engine for cold start and heating to avoid the formation of condensation within the engine when left.
You need way more power for the latter. Probably 3x more.
Do you? Have you ever been on a film set or in a tv studio? Or even worked in front of a builders light?
LeSving wrote:
We usually just leave the heaters on, but a temperature controller sounds like a good idea. Much better than any sort of timing or remote control.
We also used to leave the heaters on H24, but after the steep rise in electricity prices in 2022 we reconsidered. Our heaters are in a sense remotely controlled, too, as they are connected to the aircraft booking system. The heater starts at a time before the booking determined by the temperature. We use +5°C as the target temperature, based on Lycoming recommendations.
Btw, most of our aircraft have heaters glued to the oil sump, but the one with a Rotax engine (which doesn’t have an oil sump) has a blower instead.
Peter wrote:
You need way more power for the latter. Probably 3x more.
It’s the opposite. To ovoid condensation, it’s enough to keep the engine temp above ambient. An ancient trick on boats have been to use a small bulb (25 W) in the engine compartment. This will keep the engine nice and dry during the winter. With LED this is a bit more difficult 
but a small heating element will do. For cold start, the engine should be above +10 (or some similar number). In -30 this requires lots of heat and blankets to achieve that
Some people say leaving the heating on constantly is bad for the engine. It will dry out gaskets and stuff. I have a hard time believing that, because engines operating in desert climate does not have any such problems AFAIK.
Aha yes quite right! The objective is to reduce the RH figure, only. Like using silica gel in the cockpit to reduce RH by about 10 points (another thread).
To ovoid condensation, it’s enough to keep the engine temp above ambient
That‘s true, of course. I thought about extending my engine dehumidifier that way. I could use the Reiff preheat to keep the engine say ten degrees warmer than the dew point of the air I pump into it at all time. Would make this geeky project even more geeky 🤣
No need to measure RH, or the DP. Just heat 10K above the hangar or the OAT. 10K would greatly reduce the RH.
You can’t quote the desert as it is usually a dry atmosphere just like the arctic only warmer.
terbang wrote:
We’ve the Reiff system as well. We use a GSM switch which I usually activate in the evening if we plan an early departure.
I also have the Reiff system as pictured below plus the plate on the oil pan, and use the same SGM setup as @terbang. My absolute limit for starting without preheat is 4°C and I think the 5-6°C mentioned is even more conservative and probably better. I also have an insulated cover for the entire engine compartment from windshield forward, including covers for the propellor and spinner, as well as plugs behind the propellor. With that setup, I find that after 4 hours preheat the entire engine is nice and warm to the touch. It takes a few minutes to take everything off before flying, but I consider the extra TLC well worth it for my very expensive engine. 
gallois wrote:
You can’t quote the desert as it is usually a dry atmosphere just like the arctic only warmer.
Yes, it’s dry, and with much drier air than one could ever achieve in Europe, outside with an heating element on the engine.
