We had the 'Back burner' central heating boiler changed to a Combi, freeing up the chimney (its in the centre of the house which is a '3 bed semi
) and installed a Franco Belge 'Montfort' Mk2 Elegance (Defra Approved exempt appliance) in its place.
We burn logs that are from a timberyards off cuts and branches (so no use for anything else) and use broken pallets for kindling so zero environmental impact as they'd either go for landfill or be burnt anyway. Now at night we sit with 3 of the cats curled up on the rug together in front of it and the youngster (Fifi) just nearby cos she doesn't yet trust the others but at least the hissing has stopped now.
As for smoke/smell, we are a non-car household so don't pollute the air with fumes from those and as for 'carbon footprint' I was lucky enough to work on Watermead Countryside Park in the 80s and planted around 70 hardwood trees and 3/4 of a mile of Hawthorn hedging (alongside the canal towpath) and we have an Ash tree (self-set) and a Weeping Cherry in the garden so I think mine is in negative figures.