The units formula is printed on your gas bill. Last winter I paid 10,800, 9,800 and 8,800 respectively for using a heater and a geyser only. In summer the bill was normal like 160 rupees. I asked gas company to check the meter and they said it was working fine. I checked with other people who ran heaters and a geyser day and night there winter bill was like 700, 1200 etc. Now I suspect that the geyser is the culprit. I am testing it, it never shuts the burner (I think that the thermostat has gone) second suspect is that the insulation in geyser is gone. I have talked to my landlord and even if he did not agree on replacement I am going to replace the geyser on my expenses. Cannot pay this much bill and since last year they have increased gas price too much. check this
For all those getting higher gas bills, it is time to replace the geyser. Your bill will fall dramatically after new geyser