It is funny it's a little like Chinese whispers it all started as a fAg packet idea to stop people buying gas lol
An exploding bottle does worry me...
Spruce... Looks like you've been plugging away at this for a while then, rather than setting your heater as a demand unit did you look into it heating the water as a hot water tank (like at home) and using a controller with temperature probes to tell the unit when to fire between certain peramitters?
Yes that was a consideration. In fact a Webasto service engineer said that in his opinion it was the only way of doing it successfully. He did point out that as we use pure water, this is what would be inside the Webasto. Under design conditions as a block heater, the Webasto would be protected against frost damage with anti freeze. We would have to find a way to protect the whole unit from frost damage.
I didn't want to heat a whole 650 liter tank of water to say 40 degrees and have half go to 'waste' as we didn't use it that day. What happens if we couldn't get out that day due to sickness or bad weather? At the heat output coming from the Webasto in practice it would take around 7 hours to heat the water in the main tank. At the price of diesel, that's around £9.00. So this heater would use around three times the amount of fuel a week than my van does.
Heating the water you are using at the time makes more financial sense to me.
I've considered a separate smaller 100 litre tank, but that would take up too much space. I have considered a calorifier as a heat source, but none of the manufacturers would commit themselves on suitability. In fact, a well respected supplier into the marine industry suggested I buy one and report back to them of my findings. (They thought using a calorifier as a heat source was a good idea and if it worked, they would adopt the idea.)
To produce a raise of temperature from 9 degrees to 35 degrees (C) at 1.5 LPM would need 2.6kw of heat (from memory). So when starting this many years ago I believed that the Thermo Top C I have would just support 2 pumps with each operator stopping and starting. I presumed that the 5kw was the usable heat, so soon found out that it is a theoretical figure. About 50% of their quoted figure in our application is what is usable. This came as quite a shock to me.
If anyone is going down this route of wanting to build a cheap diesel heater, my advice is to be cautious. The Webasto Thermo Top like mine are very popular second hand as that this what is mainly used in the motor industry. However, you need one that is a universal one which is mainly sold into the marine industry. That uses a standard 'analogue' controller. IF they come out of a specific vehicle, say a BMW, they will only work on a BMW vehicle as the electronics on board will only accept 'orders' from a BMW ECU. You can buy a new circuit board that will work, but will cost £200.00 + import duty from a supplier from Turkey.
Eberspatcher is owned by Webasto as Webasto bought them out 5 or 6 years ago. Eberspatcher are more likely to be a better buy as they aren't generally vehicle specific, but, as they are less popular, spares aren't as readily available.
