Which is a better way to save energy and keep your house warm. Manual or progamable therostats

I have an Intertherm Central Electric Furance mode FEH-015H Voltage supply 240 volts Heating output 53,000BTU Appliance Number F000551240.It is only putting out warm air.Before my husband died it was throwing out hot air.What can be wrong with my furnace.To get my trailer a little warm it runs about all of the time.Before it got hot in here in no time.