My thermostat along with some others display energy use of how long the car for heat is for the furnace and air conditioner. It is close enough to the gas runtime for most furnaces. Mine I have to calculate the number of cycles and remove 2 minutes from each cycle because that is how long it takes for my furnace to actually kick the burners on. When I have done load testing on the two coldest nights of this year I just listened for it to kick on and counted the cycles to get the actual natural gas on-time.
For my 2100 sq ft house my load was 24563BTU/hr for the first 9 hours of January 21st(no sun) average temperature -7 degrees with a 78 degree difference between the outside and inside. Once I have finished my energy retrofit(non-invasive, not pulling down walls) I will be able to see the improvements in comparison to this number.
The issue with the heatmeter device is that it doesn't monitor the level of gas for 2-stage furnaces, there are 2-stage thermostats that count the call for heat time for each stage so you don't need something like this.
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