With good insulation an hour of heat in the morning from the sun shining in through the window, topped up with body heat and heat from a computer can help keep us warm throughout the day.
Consider changes we can make to use this free energy.
Repeating Challenge
In cold weather use the warmest room available. 
Repeating Challenge
Put rooms with sunny windows to good use by making sure curtains are tied back out of the way and net curtains are open when the heat from the sun is needed.
Repeating Challenge
Reuse energy from cooking by allowing it through a serving hatch to warm a living room or office.
Repeating Challenge
On cold nights consider using heat from the day at night by sleeping in the warmest room on a futon or in the room above it.
Repeating Challenge
Keep windows clean to let in more heat.
Repeating Challenge
Use dark surfaces in sunny rooms to give off valuable heat when the sun shines on them.
One-hit Wonder
Make your own radiator heat deflector sheets (4.97 Mb PDF).