I wish to start a thread that discusses the use and building of coolant heaters and block heaters as I think it will usefully improve the car for those with access to mains power when their car is parked. They have benefits even when used in summer temperatures, so you might wish to read on even if you don't live up north.
A quick rundown of the benefits of these things would be a good start, so here goes.
1. Reduced fuel consumption. On my 40 mile trip, at zero temperatures it works out at 10%. Short trips will be substantially more.
2. Reduced engine wear. About 80% of engine wear is caused because we start our engines from cold.
3. Improved comfort. The cars interior gets warm quicker, or is already warm, if the water is circulated to the heater matrix with it's fan blowing.
4. The windscreen stays fog free. If heat circulation is used, the warmed screen will not attract condensation and can even have de-iced itself for you.
All this will cost you about 15 pence at UK domestic rates, less if you have cheaper night rate electricity, or use a small heater.
I will now run through the options available to heat the coolant to get these benefits.
Plenty of cars have what is known as a "fuel burning heater" fitted. This is not something you plug in to the mains. Instead it burns the fuel of the car to generate the heat. This makes it useable anywhere you like, but it burns quite a bit of fuel in the process (about a quarter litre I think) so it is not really for us, plus they are very expensive. Don't rule them out completely for other cars though. The Volvo estates have them as a £1500 option, which initially sounds horrendous, but that should pay for itself in a couple of years and has given you a comfy car that has not worn itself out. Aftermarket firms do make these, see
http://www.webasto.co.uk/general/en/am_ ... _3177.html
Moving on to grid powered devices, there are small block heaters just like the standard Honda Insight fitment that are designed to increase the temperature of your engine coolant, especially in cold climates. The low power of these does not lend itself to you pumping the coolant to the interior heater matrix. They rely purely on convection currents to circulate the water around the engine block so when you un plug the car in the morning you have a nice warm engine and the top bit of the radiator, but the rest of the coolant is much colder. A stock Canadian Honda Insight block heater goes straight in where the block coolant drain plug is, and it works just fine. If you go this route, for gods sake make sure you do not over tighten the thing when you fit it. USE a torque wrench and do not guess. It is approx 400 watts, gets the coolant up to 180 degrees F in about two hours on a cold day. The net result of this is that the engine starts nice and easy, then the water temperature dives a bit once it starts circulating. It then takes a drive of about 1.5 miles to get back up to full temperature, rather than the 5 or 6 miles it would have taken if you had a standard cold car. You save somewhere around 10% up to 30% on short trips, and save on engine wear as well. Don't forget to un plug the bloody thing before you drive off though.
Peter Perkins is looking to combine the use of a Prius style thermos flask with an integral thermostatically controlled element and a separate circulating pump. This would be way more efficient as far as power consumption is concerned, and will allow you to trap the free heat as well as allowing you to keep the thermos piping hot, but will have limitations when warming the majority of the coolant. The power required would be so low as to even allow the use of a 12 volt dc element should you wish.
Next up are the heaters that work on the grid just like the small block heater but are more like 1,500 to 3,000 watts. These are way too powerfull to rely on just convection currents to move the water as it would start boiling! They are fitted in conjunction with an electric circulating pump which means that the entire coolant system of the car gets taken to running temperature, and should you wish, the interior of the car can get heated into the bargain if the water is allowed to flow through the heater matrix and the interior fan is made to operate. A system like this will warm a small car up in about 30 to 40 minutes. Aftermarket systems are still expensive, with some linking into the simpler car heating systems. To get the full benefit of interior heat using one of these systems, the Insights climate control system would have to have been set to "full heat" to open the coolant valve and the mode would have to be set to windshield to get any screen de frosting. On top of this, either some sort of additional fan needs to be fitted into the ducting, or the Insights standard fan would need to be isolated from the climate control circuitry using relays or whatever, and then powered up by the new pre-heater system. See
http://www.kenlowe.com/pre-heaters/cars/index.html
Now on to the back yard DIY systems, as all the aftermarket stuff costs an arm and a leg.
I am going to be talking about the powerful systems with a circulating pump from now on, as the low power, convection circulating systems are perfectly covered by Hondas standard block heater.
When selecting a heating element, it needs to be suitable for easy mounting into some sort of robust leak proof container. At the moment, in the UK, ASDA is selling a cheap "smart price" cordless kettle for £3 that has an element that fits the bill, so you won't get much cheaper than that. (Look inside and check it has a visible coiled element and check underneath to check you can see the element mounting screws)
The electric circulating pump must be suitable for hot coolant and preferably must have no shaft seals, as you would find on say the typical domestic washing machine water pumps. Look for electric automotive coolant pumps on ebay and you should see a few that will do. They seem to be about £40, and have usually been part of an oem pre-heating system. I am probably going to use a Range Rover pump that is found on the supercharged versions. It pumps coolant to the supercharger whenever the ignition is on, so it is well up to the job, is self contained, with the electric motor actually running in the coolant itself, so no seals and no overheating of the motor.
There needs to be a system in place that ensures that the pump is circulating coolant before the element is powered up so the element does not boil static coolant. This needs to cut power to the element should the circulation fail for any reason. I have heard that some aftermarket systems have indeed burnt out elements because of circulation failures.
I will leave this for now, just to see what comments it garners, and add to it as things progress. Feel free to add ideas
Benefits of Pre-heating the coolant
. In addition to the bottle there is a control valve (prevents cold thermosiphoning) and circulating pump. 
