The D5E water heater, as you are possibly aware has an additiuonal 1KW maximum heat output. Is it worth it? this really depends on your application, for example, if this is fitted to a Canal boat or Motorhome the extra 1kw might be noticed if your existing heater is struggling with heat demand - but CAUTION - with diesel heaters it's always best for longevity if you can keep the heater working at the higher end of it's output range.
Appreciate my answer is quite generalised, if you have any extra detail on your requirement please email sales@butlertechnik.com
Thank you for your enquiry