The absolutely worst time to have trouble with the furnace is during the winter season.
If the trouble with your furnace happens during a winter storm, then you are in real bad shape.
My family and I have lived in the north Midwest for 50 years. Winter weather is never a surprise. I have seen blizzards dump 2 or 3 feet of snow in less than a day and I have seen freezing rain fall like large pellets of hail. Winter is never the time to have trouble with your furnace. I can tell you this from experience, because I had trouble with my furnace this winter. I had a regularly scheduled tune up in August and the HVAC technician did not find any problems. Unfortunately, we did run into some trouble during a serious snow storm in December. I have some knowledge of heating repairs and furnace troubleshooting, but I could not repair the issue on my own and I was forced to call the heating company. Even though I called early in the morning, I still had to pay a service fee for same-day service. The heating company did not repair my furnace until much later in the afternoon and I still had to pay an additional $50 fee to have the work completed on the same day. This is the first time that I ever had to pay a service fee and I was terribly unhappy to find out about the charge. Unfortunately, I couldn’t argue with the heating company because they are the only place in this area that will service my equipment.