i use 1 thermo controlled propane heater,this runs of a 47k bottle (£30).the thing is i dont heat the whole greenhouse,the heater is positioned central under the right hand side staging,which in turn is fully cladded with polythene around it.the top bench of the staging is built of 3/4" ply which is also covered with polythene.on top of this is a layer of sharp sand covered with a sheet of micropore black polythene.i normally sow into module trays which are then covered with yet another bit of poly (to retain heat and moisture.the heater only heats the small area underneath the staging with the heat rising upwards.i can maintain a bench temp of 60c whilst the greenhouse temps never drop below 45c.i have 3 wireless thermometer probes,1 is positioned on the bench 2 is free standing in the greenhouse,the 3rd is outside.all max min and current temps are displayed on a little monitor in front of my pc.i know it sounds complicated but its so simple to operate and didnt cost that much.thers also a temperature alarm which sounds if somethings going wrong,i may have not explained it very well in words but if anyone wants some pictures of the setup id be more than happy to send some.it all makes sense when you can see it, sorry for going on a bit peterf
