Just keep the doors closed and only heat the rooms you're using. You should be ok.
---------- Post added at 10:16 ---------- Previous post was at 10:13 ----------
Hang on - just reading that PDF again - they aren't variable output, they're different models with differing outputs depending on which one you buy. So you're back to looking for a rating plate again ... actually all you need is the precise, complete model number, the PDF gives the output for each. For example the E4EU 0500 is the 0.5kW model and the E4EU 2000 is the 2kW model.
---------- Post added at 10:19 ---------- Previous post was at 10:16 ----------
According to this page:
http://www.noboheatinguk.com/techdata_spec.html
You can tilt them forwards for decorating behind - you may find the rating plate or a full model number there.