i live in a 3200 sq ft house on 1/2 acre,we love it,but its a lot of house to clean,maintain and heat,we have three teenagers,i've just had solar panels fitted for hot water and under floor heating,its a great help to the oil,at this time of year it only heats water to about 30-40 degrees,but you only need a boost to have hot water very quickly,and great for under floor,as your building i would consider something on those lines,best of luck,yob