For info if anyone's interested, i bought parasene heater as most have done for shed  / garadge static systems but also got an oregon scientific thermometer.  The advantage of this is that is has a remote sensor that you put in shed / garadge with main thermometer in house reading temp.  You can set an alarm to go off at indicated levels so if there is a problem with possible freezing (heater thermomstat set too low?? / heater broken etc)  you will get an alarm  warning.  Remote up to 30 mtrs.
I found it useful anyway !!  
£30
code 0S EMR899
wEATHER FRONT LTD