Is there a way to find out how often your furnace is running?
Some of the more advanced thermostats will track how often they are running.  I have a Filtrete Wifi-Enabled Progammable Thermostat.  It gives you a per-day total of how often the heat and A/C are run.  You can also download an hour-by-hour export of the usage in CSV format.

I am in no way affiliated with this company. It is simply a product I have installed at home

It also gives you an idea, for a given temperature change, what the % change in heating cost will be: