I have a link for the one in Bulgarian, I tried adding "_en" and voila - http://www.nsi.bg/census2011/PDOCS2/karta_Census2011_en.pdf
It's "availability of heating system" and I think that excludes stoves and small electrical heaters, especially given the next question. But I guess it could be interpreted either way.
Here's a funny thing in the translation - the "energy saving woodwork" is not made of wood.