Is it possible to calculate energy efficiency of a flat by knowing how much energy was consumed for heating?

During 6 days my heating system consumed 11,4 m3 of natural gas keeping its temperature at 20 degrees of Celsius. No human or other energy source (except for refrigerator) was inside the flat at that time.

Outside temperature was about 0 degrees of Celsius (but I can provide more accurate temperature data set).

Is it possible to calculate energy efficiency of that flat by knowing how much energy was consumed to keep temperature?

• What heating source do you use? Does it have an efficiency rating? The main uncertainty in the calculation is the amount of heat leaving through the chimney/exhaust.
– user2451
Commented Jan 26, 2016 at 13:23
• Ah indeed, I didn't take it into account. Commented Jan 26, 2016 at 13:27
• What do you mean by the "energy efficiency of the flat"? That could mean various things. Another way to approach the same question: how would you use the information? Commented Jan 26, 2016 at 18:40
• To measure the overall thermal resistance (R rating) you'd need to know the temperature difference and also how much air was moving in and out. But as @EnergyNumbers says, what would you do with that information? StackExchange works better with concrete problems.
– Ⴖuі
Commented Jan 27, 2016 at 7:04
• Things with energy efficiency expressed as percentage are normally machines of some sort that use one type of energy and do some useful work, e.g. an electrical transformer or a winch. A flat isn't like that - it isn't built primarily to do physical work.
– bdsl
Commented Jun 19, 2016 at 9:43