The phrase "open hearth" refers to a type of furnace used in the past to melt metals. It had an open fire that allowed easy access for adding or removing materials. Full definition
Between secondary school and college, she painted houses, demonstrated open hearth cooking for museums, and opened a café. (bookbrowse.com)
During the winter months, the Tarragona Lodge open hearth fires add to the allure of the accommodations. (travelground.com)
Coal burning in power stations is far more efficient than smoky inefficent open hearths and consequently far less particulate carbon gets into the air from each ton of coal burnt. (wattsupwiththat.com)