How does changing heathing from gas to electricity influence the bill?

The answers aren't so easy either. If you don't have a night meter for electricity you can expect a significant increase. The extent of increase or decrease will likely depend on the type of heating you install. If you install some kind of system which heats up water using cheap electricity at nights the saving of course will be much greater. But, at what cost??? The question on double glazing is also not so easy to answer. If there is a large amount of heat leakage around your present window frames you will save a lot of heat by replacing them. But if the frames are in good shape and you add only another layer of glass the difference may be less. So, no easy answer. It's a question of savings vs. investment in new materials.