No you won`t crack any windows with it unless your working in Antarctica,and as for fitting the Varitech heater i would get a good motor mechanic to fit it for you someone that knows a bit more than most,the fuel lines on the heater and small pump although look simple to fit are not as straight forward as you would first think.Also as van floors have ridges on them it`s a good idea to fit small brackets either side of the heater in order for it to sit flush on the van floor,fitting it as it is on a van floor would leave it looking lop sided or Pi**ed.Like i say it looks simple and is to the right person but i wouldn`t attemp it myself with basic knowledge,also bear in mind they weigh a hell of a lot more than you`d think aswell.