How can I extend the length of my furnace run time after burner shutdown?
I too am like you, an old time boiler guy; 40+ years + 11 retired. My comment to you is, if your furnace fan is running on the correct fan speed and the furnace is not too oversized, the heat exchanger should be able to give up (cool down) enough so that there will be a very little waste of energy. The small amount of energy you are trying to remove may be offset by the energy the fan motor will consume. Yes, I still like the old ways that we were used to but that was then and this is now. Get used to it, the new generation has made us obsolete.