How many kilowatts does it take to heat one litre of water in one hour?

any similar formula would also be very helpfull e.g. the same but for 1000 litres and i can adjust the formula to suit my needs. Many thanks if you can help

It depends how much you want to heat the water up by:

As a general rule, the energy (in joules) to heat water is given by:

Energy = mass of water (kg) x temperature rise (celsius) x 4200

1 litre of water has a mass of 1 kg

The power in watts is then found by:

energy (joules) / time (seconds)

To convert that answer to kilowatts, divide by 1000.
It depends on how MUCH you want to heat the water. A kilowatt will raise the temp of one kg (one liter) of water by one degree celcius in one second.

(a watt will raist the temp of one cc (one milliliter) by one deg. celcius in one second. with that you can scale it for any amount of water or heat or power)
Do you mean 'boil'...?
Thats very vague - what's the start and end temperatures ?

To heat 1 ml of water takes 4.18 Joules per degree C, the specific heat capacity. 1000 watts is 1000 Joules per second, but spread over 1000 ml. So thats 1/4.18 degrees per second. (0.239 deg C).

To go from say 15C to 100C would take 355 seconds at 1kw
To do the same rise in 3600 seconds, takes 0.0986 kW for 1 hour. So thats using a heat equivalent of a "100w" light bulb.
I'd want my tea much quicker than that.
The energy required to heat water is the same, regardless of what method is chosen.

This is because the laws of physics dictate the energy requirement, not the type or brand of product.

Every liquid has a "Specific Heat Capacity" value.

In the case of water that value is 4.187kJ / kg K.

This means that 4.187 Kilojoules of heat energy is required to raise the temperature of one kg mass (one litre) of water by one degree C at standard temperature and pressure.

Work and heat can both be described using the same unit of measure. Sometimes the calorie is the unit of measure, and refers to the amount of heat required to raise one (1) gram of water one (1) degree Celsius.

Heat energy is measured in kilocalories, or 1000 calories.

Typically, we use the SI units of Joules (J) and kilojoules (kJ).

One calorie of heat is equivalent to 4.187 J. You will also encounter the term specific heat, the heat required to raise one (1) gram of a material one (1) degree Celsius.
Specific heat, given by the symbol "C", is generally defined as:

C = q divided by [M delta T]


C = specific heat in calories/gram-degrees Celsius
q = heat added in calories,
M = mass in grams
delta T = rise in temperature of the material in degrees Celsius.

The ability of any particular system to deliver this heat energy is governed by its efficiency.

If a system requires twice as much energy to what can be extracted (in the form of hot water equivalent) then the system has an efficiency of only 50%.
Yes it has all been said really.Just wanted to point out kilowatts is a power output or rate of consumption of energy.If you need to know how much electrical energy you will need to use then you must work out how many joules are needed.
Less kilowatts will just take longer.Or less kilowatts will not heat the water as much in any given hour.

The answers post by the user, for information only, does not guarantee the right.

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