Warm Air Oil Furnace Before & After Installation The #barracudateam changed out a wood/oil combo and installed a new #Kerr #Gemini warm air furnace the other day... here is a before and after! Kerr Gemini Warm Air Furnaces are the highest efficiency non-condensing oil-fired furnace on the North-American market. With BTU ratings from 70,000 to 140,000