Daz why don't you go the diesel heater route?
for the cost i dont think its worth it mate.initial installation,ongoing running costs(diesel,servicing etc).plus ill be getting a brand new van every 5 years from now on.
im already spending over 10k a year on expenses,taxes and insurances before ive even made a single penny in profit.you gotta draw the line somewhere as a sole trader.
cold water works just fine.the time saved and added cleaning ability of hot water is marginal.not enough difference to justify the extra cost of a pro diesel heater IMO.
I installed a fastar 8l a week or so back and i think it's great....I think hot cleans a lot better 
Could not agree more SB as hot most defo cleans a lot better than cold.
This is a bit of a silly statement, I don't think anybody will disagree that hot water doesn't clean better, for a start if hot
enough it has the ability to melt.
So the question is what are you getting off the glass that cold users aren't ?
The answer is nothing otherwise cold wfp cleaning would have never taken off, at the end of the day your opinion is totally
based on your speed which for the majority of cold users isn't an issue.
That's why I compare it to things like parts per billion machines which at the end of the day are nothing more than confidence
builders.
Using hot is just a confidence builder my arse. lol
Even dazomond noticed the difference going back to cold or he would not of started this post now would he?
Off course its a confidence builder, there's a video on youtube of a guy cleaning a detached property with a backpack
who does the front in under 2 minutes so hot wouldn't make him any quicker unless he hadn't the confidence to go at this
speed.
Back when I first started wfp cleaning I was told that purified water cleans better as it absorbs/eats the dirt, total nonsense but because I believed it I was then able to clean quicker as that belief meant I was more confident in the method.
We see what we want to see.
I see a lot of one-off, irregular and even regular cleans that are filthy. Using hot just melts away the likes of dried on tree sap, traffic film, algae, lichen, snail trails, bug/bird poo etc on plastics and glass. I'm not really that interested in how much quicker it is but how much easier and better hot cleans.
As far as that vid is concerned anyone including myself can be a cold splash & dash merchant. Which may I add has nothing to do with confidence either. lol