After upgrading insulation and windows and replacing a 30 year old 120k NG furnace with a 75k 92% unit, my calculated heat loss went from 110,000 to 32,000 btu/hr. At a setpoint of 19C with outside temp of 5C the house will maintain 18.5-19 for several hours. The furnace cycles TWICE a day for,20-30 mins in the morning and the same in the evening. I set it back to 16 overnight.
Now I'm wondering if the new furnace was a waste of money. With such a significant reduction in heat loss, the old furnace would have probably cycled about the same as the new one with a slightly larger fuel consumption. Before the energy upgrades the old furnace would cycle twice per hour under the same conditions. I suppose the bottom line is that furnace replacement payback is going to me much longer when combined with major energy upgrades.