Have I missed a post.. what have you actually purchased? I presume a Webasto
Mine runs about 3l in a 6 hour working day. When I first bought it I read the specs that says 9.1kw uses 1.1l an hour and expected a lot more fuel usage. But it idles quite a lot in between jobs and moving around so on. I also think they run on around 7kw when up to temp with a one man set up. So using under 1l per hour.