Open Fire What are the options for Energy Efficiency

Stovax insert stoves are excellent - beautiful piece of kit and heat from just burning seasoned wood is great clean burn system ensures glass doesn't get discoloured. Are expensive but you will have it for 20+ years
 
Over time, dont the windows of those stoves go all black and you cant see the flames? Thats what I have heard from other people.
But maybe they dont clean them enough?
Mine has a top air inlet as well as a bottom inlet that draws down over the glass which helps to keep it clean