oil furnaces sometimes lack the 24v control to turn on the blower unless a/c is part of the system - then you have a transformer on the oil primary and a g terminal. look for the fan limit control - may have a white button to turn the fan on manually. be aware of your increased electric usage and change filters more often. on an older willamson, you have a belt-drive blower, so check the belt, don't over-tighten. running an old belt-drive unit continuously will result in bearing problems, noise, motor failure unless you have a really good service guy who has pulled the blower and addressed these items. remember that trying to use the g lead from the thermostat requires a 24vac source and a relay at the furnace - don't run line power to the stat!