Wood pellet to be really efficient needs to be a dedicated unit i.e. it will only burn wood pellets that are fed from a hopper into a small combustion chamber, multifuel stoves are fine if you can get coal which you can't in Portugal so your fuel source is wood, exactly what is your looking at??
It's not how many radiators it would heat but what area are you trying to heat you need that calculation to find out the type of rating stove/boiler etc you need.
It's not how many radiators it would heat but what area are you trying to heat you need that calculation to find out the type of rating stove/boiler etc you need.