Is the 5kw sufficient to heat a 20 x 20 insulated garage?

The Reznor EGW-5 Electric Unit Heater 5 kW unit will be too much heating for your required space. The Reznor EGW-3 will be a better option as it will have the recommended BTU for your garage. If you have any further questions we recommend that you give us a call. Thanks!