Had my HVAC system updated.  Installed an American Standard system with a heat pump.  The heat pump works out to cost the equivalent of LPG @ $0.90/gallon.  i.e. it is more cost effective to use the heat pump unless I can buy propane for $0.90/gallon, assuming electricity is @ $0.10kW/hr.

The yellow bars show when the heat pump is operating, and the red when the furnace (using) propane. As you can see once the heat pump had been enabled it has been used the majority of the time. This has really cut my propane use, and will doubtless not make me popular with my supplier!