Dakota wrote:
Perhaps some magazine, or an individual, could run a test. It just feels like the furnace really works hard and long to bring up the temp from 60 to 70. What if it was held steady at 68. I am not sure the answer is so clear cut.
There has been a huge amount of research done on this. You can find plenty of data if you search the web. Good places to look are Home Energy magazine, the Department of Energy - Energy Efficiency and Renewable Energy Program - Building Technologies Program, and the Rocky Mountain Institute, among many others.
The furnace works no harder to bring up the temperature further. Since the thermostat is simply an on-off switch, the furnace is putting out the same output all the time, but for longer periods to bring up the temperature more degrees. Actually, it is generally harder on furnace components to cycle a lot, which is what happens when you maintain a warm house 100% of the time. The furnace behaviour is simply a function of heat flow.
As to the science of it, heat is constantly flowing out of a warm house through convection, advection and conduction. The rate of heat flow is governed by: 1) the temperature difference between inside and outside ;and, 2) by the materials the heat must flow through. if you put in weatherstripping and insulation the rate is much reduced. The furnace just injects heat to make up for the loss, therefore if you keep that temperature difference high all the time (leaving the thermostat at one setting), the heat flow is dramatically increased, ergo your furnace has to produce that much more heat to compensate. Very simple equation.
If your furnace has to run an unusually long time to bring up the temperature, then that means that either: 1) the furnace is undersized for the space; or, 2) your weatherstripping or insulation is inadequate.
