What an hour of gas cooking really costs: the math nobody shares
The 7.5 kW on the label is the hob's total power and equals hourly consumption at full flame. Here's how to convert it into cubic metres and euros.
English · Original discussion in Spanish · Published
Cooking for an hour on a single gas burner costs cents, not euros
The label on a natural gas hob says it all, yet almost nobody reads it: EQn 7.5 kW and 545 g/h. Translated, the entire hob on full power consumes 7.5 kilowatts per hour, and each burner works independently: the auxiliary burner 1.00 kW, the two semi-rapid burners 1.75 kW and the rapid burner 3.00 kW. The question that sends half the internet searching for "gas hob consumption" is whether those kW are per hour. They are. A burner's rated power is, in practice, its hourly consumption at maximum flame.
What EQn 7.5 kW 545 g/h on the sticker means
The manufacturer's label mixes two units because the same appliance can run on different gases. The 7.5 kW is the total power of all four burners added together. The 545 g/h is the equivalent consumption when the gas is butane or propane, measured in grams because it is sold in cylinders. With natural gas, the reference is cubic metres and pressure in mbar: G20 at 20 mbar is the Spanish domestic network, while G25, G30 at 28-30 mbar and G31 at 37 mbar correspond to other mixtures and to butane-propane.
The code ST6XG321 is no mystery: it identifies the hob family, not the pressure. And that's where the manufacturer's useful information ends. Not a single line about euros.
Converting kW into cubic metres and euros
The conversion is the part that trips people up. A 3.00 kW rapid burner lit for one hour consumes 3 kWh of energy. Natural gas delivers roughly 12.5 kWh per cubic metre, so that burner uses about 0.24 m³ in sixty minutes. The 1.00 kW auxiliary burner, just 0.08 m³. The full hob at maximum, the 7.5 kW, comes to around 0.6 m³ per hour.
If you want a comparison, the equivalence that circulates is the butane one: a 12.5 kg cylinder yields about 112,000 kcal, equivalent to 12.5 m³ of methane. With that, anyone with their tariff in hand can work out the cost without relying on a technician.
Why there is no official consumption figure per burner
The short answer: because the manufacturer declares power, not cost. Actual consumption depends on the flame you use, how long the burner stays on low and whether you put a lid on the pot. An hour of home cooking is not an hour of four burners at full power, not by a long shot.
The long answer is that the figure people are looking for isn't in the manual because the manual is written for the installer, not for the user who wants to know what Sunday's stew costs them.
The calculation that actually tells you what cooking costs
Multiply the kW of the burner you use by the hours it is on, divide by 12.5 to get cubic metres, and apply the price of the consumption term on your bill. The result, for a 1.75 kW semi-rapid burner over one hour, is 0.14 m³. With the natural gas price on your bill, the final figure is cents, not euros.
Is it worth changing hobs to save money? With these numbers, the answer answers itself.
The label on a natural gas hob says it all, yet almost nobody reads it: EQn 7.5 kW and 545 g/h. Translated, the entire hob on full power consumes 7.5 kilowatts per hour, and each burner works independently: the auxiliary burner 1.00 kW, the two semi-rapid burners 1.75 kW and the rapid burner 3.00 kW. The question that sends half the internet searching for "gas hob consumption" is whether those kW are per hour. They are. A burner's rated power is, in practice, its hourly consumption at maximum flame.
What EQn 7.5 kW 545 g/h on the sticker means
The manufacturer's label mixes two units because the same appliance can run on different gases. The 7.5 kW is the total power of all four burners added together. The 545 g/h is the equivalent consumption when the gas is butane or propane, measured in grams because it is sold in cylinders. With natural gas, the reference is cubic metres and pressure in mbar: G20 at 20 mbar is the Spanish domestic network, while G25, G30 at 28-30 mbar and G31 at 37 mbar correspond to other mixtures and to butane-propane.
The code ST6XG321 is no mystery: it identifies the hob family, not the pressure. And that's where the manufacturer's useful information ends. Not a single line about euros.
Converting kW into cubic metres and euros
The conversion is the part that trips people up. A 3.00 kW rapid burner lit for one hour consumes 3 kWh of energy. Natural gas delivers roughly 12.5 kWh per cubic metre, so that burner uses about 0.24 m³ in sixty minutes. The 1.00 kW auxiliary burner, just 0.08 m³. The full hob at maximum, the 7.5 kW, comes to around 0.6 m³ per hour.
If you want a comparison, the equivalence that circulates is the butane one: a 12.5 kg cylinder yields about 112,000 kcal, equivalent to 12.5 m³ of methane. With that, anyone with their tariff in hand can work out the cost without relying on a technician.
Why there is no official consumption figure per burner
The short answer: because the manufacturer declares power, not cost. Actual consumption depends on the flame you use, how long the burner stays on low and whether you put a lid on the pot. An hour of home cooking is not an hour of four burners at full power, not by a long shot.
The long answer is that the figure people are looking for isn't in the manual because the manual is written for the installer, not for the user who wants to know what Sunday's stew costs them.
The calculation that actually tells you what cooking costs
Multiply the kW of the burner you use by the hours it is on, divide by 12.5 to get cubic metres, and apply the price of the consumption term on your bill. The result, for a 1.75 kW semi-rapid burner over one hour, is 0.14 m³. With the natural gas price on your bill, the final figure is cents, not euros.
Is it worth changing hobs to save money? With these numbers, the answer answers itself.
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Summary of a discussion on Burbuja.info - Foro de economía, actualidad y política., translated from Spanish and reviewed before publication. Read the full discussion (2 replies).
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