Mega Joules: MJ to kWh – KJ to MJ – MJ to KJ – MJ to Joules – Megajoules to Kilowatts

Mega Joules: MJ to kWh – KJ to MJ – MJ to KJ – MJ to Joules – Megajoules to Kilowatts

Mega joules (megajoules – MJ) is a unit of energy typically represented by the symbol “MJ”.

Megajoules per hour (MJ/hr) indicates gas consumption of the appliance, not the heat output.

The prefix “mega” infers one million and mega joules (megajoules – MJ) equals 1,000,000 joules, an SI unit of energy with the plural “mega joules” or MJ.

The prefix “kilo” infers one thousand so 1 kilojoule equals 1,000 joules

So, for KJ to MJ (KJ to megajoules or kilojoules to megajoules), 1,000 KJ equals 1 MJ

The inverse, for MJ to KJ,  is 1 MJ equals 1,000 KJ

For, MJ to joules (MJ to J) , 0.001 MJ equals 1 J (joules)

What are megajoules (mega joules – MJ) and why does it matter when I buy a gas heater?

What size gas heater should I buy?

Many people think they know but you might be surprised by the real answer…

What is a MJ – Mega joules?

♦ MJ is the symbol for Megajoules (mega joules – MJ), which is a unit of measure relating to energy.

♦ Mega joules (megajoules – MJ) are based on a joule, which is the standard unit of energy in the International System of Units.

♦ As “mega” is the prefix for one million, for MJ to J, a megajoule (MJ) equals one million (1,000,000) joules (J).

♦ The energy content of LPG and natural gas are both measured in mega joules (megajoules – MJ).

♦ In the context of a gas appliance, mega joules indicates the consumption of gas per hour – MJ/hr.

♦ Mega joules are sometimes incorrectly referred to as the heat output of a gas appliance.  It is not.

♦ Kilowatt (kW) is the correct unit of measure for expressing heat output.

♦ How is megajoules (megajoules – MJ) pronounced? Say it as if it were spelled “mega jewel” or “mega jewels”, not “mega jowl”.

Keep reading for the details on all of the above…

MJ to kWh (MJ kWh) – Megajoules to kWH – Megajoules to Kilowatt Hours

MJ to kWh, megajoules to kilowatt or hours, megajoules to kWh, megajoules to kilowatt hour and megajoules to kWh are just five ways to say the same thing.

MJ to kWh is probably more correctly stated as MJ/hr to kWh, as then both are consumption over time.

For megajoules to kilowatt hours or MJ to kWh (MJ/hr to kWh), 1 megajoule (MJ) = 0.278 kWh.

So, 1 MJ to 0.278 kWh

kWh to Megajoules

kWh to Megajoules (kWh to MJ) is the measure of heat output to gas input.

1kilowatt (kWh) equates to 3.6 mega joules (MJ).

3.6 mega joules of input equals 1 kilowatt hour of output at 100% efficiency.

so, 1 kWh = 3.6 MJ

MJ to KJ – Megajoules to Kilojoules

How many megajoules to kilojoules (MJ to KJ)?

There is 0.001 megajoules (MJ) to 1 kilojoules (KJ).

So, for MJ to KJ, 1 MJ to 1,000 KJ

KJ to MJ, KJ to Megajoules or Kilojoules to Megajoules

How many KJ to MJ – kilojoules to megajoules or KJ to megajoules?

There are 1000 kilojoules (KJ) to 1 megajoules (MJ).

So, for KJ to MJ (KJ to megajoules), 1000 KJ to 1 MJ

MJ to Joules, MJ to J or J to MJ

There is 0.000001 MJ in 1 joules (J)

Conversely, there are 1,000,000 Joules (J) in 1 MJ

So, for MJ to joules, 1MJ = 1,000,000 J

Mega joules is NOT Heat Output

I once watched a product video produced by a major Australian retailer.

In it, a “Product Expert” reviews a Rinnai gas heater.

The problem was that the presenter lost me in the second sentence when he said:  “That’s 13 mega joules of heat.”

This is an incorrect statement and perpetuates a common misconception that mega joules represents heater output, as opposed to gas input.

Gas Consumption is in Megajoules per Hour (MJ/hr) — Not Just Mega joules (MJ)

Megajoules per Hour (MJ/hr) ratings on appliances actually indicate the gas consumption of the appliance, not the heat output.

On the other hand, heat output must also take into account the relative energy efficiency ratings of the models being compared.

The Mega joules per Hour (MJ/hr) gas consumption rate is often erroneously expressed as just “MJ”.

This is how MJ is frequently used in reference to gas appliances.

Kilowatt to Megajoules, kW to Megajoules or kW to MJ

Kilowatts (kW) is how gas heater output is measured.

To convert kW to megajoules or kilowatt to megajoule (kW to MJ),kW to MJ conversion:

1kilowatt (kW) equals 3.6 mega joules (MJ).

3.6 mega joules of input equals 1 kilowatt of output at 100% efficiency.

so, 1 kW = 3.6 MJ

Megajoules to Kilowatts, MJ kW or MJ to kW or Megajoules to kW

Heat Output = Kilowatts or kW

To convert MJ to kW, convert megajoules to kilowatts or megajoules to kW (MJ kW):

So, 1 MJ = 0.278 kW.

However, no gas appliance is 100% efficient.

That is why we have Star Ratings, so we can compare relative efficiency between models.

Appliance output is often expressed as just kW.

What about kWh to MJ – Kilowatt Hours to Megajoules

kWh to MJ (kilowatt hours to megajoules) is the cumulative consumption of energy over time, measured by the hour.

kWh to MJ (mega joules) is probably better stated a kWh to MJ/hour, as both are units of energy over time, measured by the hour.

For kWh to MJ (kWh to MJ/hr):

So, 1 kWh = 3.6 MJ

MJ to kWh (MJ kWh) – Megajoules to kWH – Megajoules to Kilowatt Hours

MJ to kWh is probably more correctly stated as MJ/hr to kWh, as then both are consumption over time.

For MJ to kWh (MJ/hr to kWh), 1 megajoule (MJ) = 0.278 kWh or better stated as

So, 1 MJ = 0.278 kWh

Gas Heating

Gas heating is the heating of a room or outdoor area using a gas space heater fueled by natural gas, LPG (propane or butane) or biogas.

Indoor gas heater types include unflued portable gas heaters, flued gas heaters, radiant gas heaters, convector gas heaters, radiant-convectors, and gas fireplaces.

Gas Heater

A gas heater is a space heater used for room heating or outdoor area heating fuelled by natural gas (including CNG and LNG) or LPG (propane, butane or a mixture of the two).

The two general types of home gas heaters are flued gas heaters (vented) and unflued gas heaters (unvented).

Energy Efficiency – Star Ratings

Star ratings were developed to provide consumers with an easy way of comparing the energy efficiency of different models.

All States now require both LPG and Natural Gas heaters to be tested and certified, under AS4553, by independent testing organisations, such as the AGA and SAI Global.

The Star Rating is based on net heater efficiency.

Net heater efficiency is calculated on the basis of a combination of efficiency measures and takes into account all gas and electrical inputs.

It basically compares the amount of raw energy input consumed by the heater in comparison to the heat energy output provided.

Remember, for MJ to kWh (MJ/hr to kWh), 1 megajoule (MJ) = 0.278 kWh or better stated as 1 MJ/hr = 0.278 kWh

To convert kW to megajoules (kW to MJ), 3.6 mega joules equal 1kW at 100% efficiency.

This is calculated as a percentage and then translated into the corresponding Star Rating.

Please see Energy Efficiency & Star Ratings for Gas Heaters

What Size Gas Heater Do I Need?

What to Consider

If you buy too small a heater, it will not be able to adequately heat the intended area.

Heating Area Volume & Climate Zone

Very Cold Zone: 1kW output required for each 8.5m²

Adjustment Factors

Gas Heater Sizing Example #1:

Gas Heater Sizing Example #2:

Use kW not MJ – kW to MJ – MJ to kWh

Energy Efficiency Matters – Star Ratings

Minimum Room Sizing

Manufacturer Sizing Charts

Final Thoughts on Mega Joules