What makes stoves so efficient?

[Stubby]

Just get the smallest Burley stove . It has a well insulated fire box with a single double glazed door giving high efficiency rating

[benedmonds]

If space is an issue get an inset stove. 

https://goo.gl/images/NsGBpj

We have a narrow lounge and found this took up the least space. 

[slim reaper]

You may find that fitting a free standing stove and compliant hearth eats quite bit of space out of a room space..inset stoves as suggested are neat , Stovax Riva belt out some heat for their size 

[Alycidon]

The installation of a register plate into the base of the chimney to prevent heat loss up the chimney is the single most important reason why a stove provides far more heat into the room compared to an open fire.    I looked at two earlier this week due to poor heat outputs., they had no register plates and flue pipes around 2mm away from oak lintels that were badly charred, builder install in 2005, am amazed the lintels have not caught fire.  Thus all the heat generated goes straight up the chimneys.

 

A