Posted: 05/12/2013 at 13:41
An electric heater with a thermostat will only come on when it reaches the set temperature. The warmest part of the day in winter tends to be during the day so it may not come on at all during the day. I would not worry about those being left on.
My GH has no electricity so I use paraffin heaters and if it is forecast to be low temps all day I just leave it on - fuel lasts for 5 days if needs be.