The amount of electric heat output is directly related to the voltage delivered to it. Small electric heaters are not for heating large spaces. They are for small rooms and spot heating. If the home has not been kept up to temperature you could have problems getting it up to temperature.
The heating guy should have taken the supply voltage readings at the heaters, made sure all the elements were working, and taken a temperature rise across the heaters.
How old are the heaters? If you can find a temperature rise spec for them, and know the temperature in and out, you can pretty much determine how they are working. Like Zander stated, it would also help knowing what the home requires in BTU/HR to heat it.