For the highest levels of performance the glass fronted, Riva multi fuel cassette fires offer up to 81% heating efficiency. This is because the airtight door and the latest cleanburning technology incorporated into the highly developed, firebox allows for greater control of the combustion process. Open fires are not always the most efficient at heating your room. The Riva Open Convector fires, however, give you an open fire and heating efficiency twice that of a normal grate or hearth fire. This is because the Riva Open Convector fires produce warm convected air as well as radiant heat.