You won’t need to actually measure loss of each component because calculations will be accurate enough. You should measure overall heat loss, however, so you can plot your progress. Invest in an electronic thermostat that also displays the number of hours that your furnace is on per day and cumulatively from the time you reset the counter. Establish a baseline measurement, such as the number of hours of heat used during the month of February, and record the average daily temperature (it’s available on your energy bill) as well as the average daily temp inside your house. This will allow you to calculate the savings in years to come.
To figure out where to put your money and effort, calculate heat loss through each part of your home. Charts like
http://coloradoenergy.org/procorner/stuff/r-values.htm"
give you the insulating efficiency (R-value) of different building materials, from which you calculate heat flux as
\dot{Q}=A(T_{outside}-T_{inside})/{Rvalue}
where A is the area.
Example; I bought an old house in Colorado that had a 7’x9’ single pane sliding glass door with a highly conductive aluminum frame. The window was iced over most of the winter and the family room was uninhabitable. If the average R-value was about 0.6 and the daily average difference between indoor and outdoor was 30F (mild winter), then
\dot{Q}=3150 Btu/hr. Sorry about the British units but that’s what’s used in the US HVAC and energy industries...
I installed a double-pane Low-E French door assembly with insulating shades, R-value about 3.3, so the savings is about 2.5kBtu/hr or 1.8e6Btu/month. My gas furnace is about 82% efficient (value available from the manufacturer) for a savings of 22 therms or $15-25 per month (natural gas prices vary from year to year) from just this one item. We would have done this upgrade for aesthetic reasons anyway, but with this kind of calculation I could determine the benefit (and also balance what sort of window with how much insulation versus cost).
Here are the rules of thumb:
1. Seal all drafts first. They are the biggest winners, while conversely if you don’t take care of them they’ll undo the effectiveness of any other improvements. Many of the biggest ones are hidden; for instance, the vertical chase of each “wet wall” (space for pipes behind your tubs and showers) is usually open to the attic.
2. Next take care of the most egregious offenders, like the window discussed above.
3. Next go from top to bottom.
a. Attic is a huge area and is easy to upgrade. Roll out new unfaced (so they breathe) R-25 fiberglass batts to bring the thickness to around 12 inches (R-38). Fiberglass is so cheap that this is a big win.
b. Next do windows, and garage walls (insulate and drywall) and door (insulated unit) if you have rooms above.
c. Can’t do much with walls unless you want to demolish the house. R-15 is typical for wall with 2x4 studs, R-11 insulation, drywall inside and wood sheathing outside.
d. Last in effectiveness is under-floor insulation.
4. You mention a more powerful furnace; if you insulate your house, you may get by with a smaller one instead, as I did. Upgrading the furnace will save money if existing furnace is old and inefficient. New furnaces are 80+ to 90+% efficient compared to 60-70% for 30 years ago.
The cold rooms in my house are now comfortable and the furnace rarely turns on unless in gets really cold outside. The calculations predicted pretty well the energy savings I actually observed (this isn’t rocket science after all…)
You can get more sophisticated later if you want. I've measured the thermal time constant of my home (it's now about 40 hours), the effective heat capacity, etc. These are amusing for a physicist, but the simple equation and chart above are all you really need.
Have fun!
