Orangeries were often built in the grounds of large houses. not only to grow exotic fruit but also to impress guests with their wealth and status.  The orangery at Dalkeith which was built almost 200 years ago was heated by an under-floor system which used a ton of coal each day, which was not a problem for the Dukes of Buccleuch who owned several coal mines.  During the 1940s and 50s It was badly damaged and there are plans to restore it now while meanwhile a tent-like roof has been added to slow down deterioration. 
Thanks to Bobsblips for the “Something historical” challenge