To calculate the efficiency of the space heater, you can use the formula for efficiency:
\[ \text{Efficiency} = \left( \frac{\text{Useful energy output}}{\text{Total energy input}} \right) \times 100% \]
In this case, the useful energy output is the thermal energy produced, which is 896 joules. The total energy input is 1,400 joules.
Plugging in the values:
\[ \text{Efficiency} = \left( \frac{896 \text{ joules}}{1400 \text{ joules}} \right) \times 100% \]
Calculating that gives:
\[ \text{Efficiency} = \left( 0.64 \right) \times 100% = 64% \]
Thus, the space heater’s efficiency is 64%.