I have never heard of any fire hazard due to electrical heaters
I tend to agree; I was just trying to get myself into the head of the average risk management (the latest MBA fashion) type around the UK 
I must say that I have not found it very effective
I reckon you would need way more energy to heat up a 200kg IO540 lump than a tin of beans.
There is also no way to spread the heat fast enough; if you applied say 100kW to the engine sump, it would melt the sump without doing anything anywhere else. I reckon the most one can apply on the bottom is a few hundred watts, and I will leave it to somebody whose Physics O-Level is more recent to work out how long that would take to raise say 50kg of ally + 150kg of steel, with their respective specific heat capacities, by say 20K.
That’s why the “claimed best” products involve heating the engine at many places, with little heaters screwed all over the place. The installation of that one must be a big job.
Many thanks for the feedback, all… Today my engine was about -2C and started immediately, so I have the one data point!
And regarding hangar fires: They come from where you least expect it… Our hangar is heated and has a maintenance facility, so no need for aircraft heaters, but a chance of the mechanics getting something wrong. Nonetheless our only hangar fire so far was caused by the paramedic of the rescue helicopters that used to be based there (their operation was moved to another hanger not long after that accident). During his daily systems check in the morning, he opened one of the oxygen bottles which ignited some flammable stuff in the vicinity. Luckily the ground crew was very quick at pulling the platform, on which the helicopter was parked, out of the hangar. In one of the pictures “my” aircraft can be seen which was parked right next to it. Oxygen bottles are much more dangerous than engine heaters or soldering irons, obviously!
Those aircraft which subscribe to the ArmStrong starter brand, become recalcicrant at around -5C.
Pet hair dryer?
http://m.ebay.co.uk/itm/171506494179
Awesome!
I can think of alternative uses for that 2.8kW device, for certain types of pets 
I have one – not in that colour scheme. It dries the Newfoundland but no way it would warm your engine to be worth the trouble.
This is how we heat our engine. We have 2 × 3kW electric heaters:
We had a long discussion on this in a German forum. The bottom line was that any unattended heating is a major insurance problem and for example the local hangar owner would not officially allow it. The only exception might be one of those STC solutions which are then regarded as part of the plane and covered by the plane insurance. And applying common sense I think unattended electric air blowers are just too much risk. Who knows if some plane in the hangar is not spilling fuel on the floor and then the remote controller heater might do the rest…
So my approach is as much heating power as possible using standard equipment which does not look like a DIY explosive device. This way in 20-30 minutes the plane is ready to go. We share the system with others in the same hangar and reduce the costs.
Sebastian, where did you source the heaters from?
From an engine point of view, my Thielert (sorry, Continental) Diesels probably can be started at ‘any’ temp. However, the fuel type dictates some limitations: not colder than -30 degrees C for AVTUR and not colder than -5 degrees for Diesel fuel.
