Most common in older homes are draughts, which can be due to cracks or unsealed windows or gaps through your doors. Draughts can let the frosty air into your house which means your heating has to work harder to keep you and your home warm.
If you suspect you have draughts, do a quick check to try and locate it, when you find the suspected draught, if it’s from a door, try using a door snake or if it’s from a window, you might need to visit a hardware shop and get some seal or no more gaps.
Another effective way to keep your home warm is to close the curtains before it gets dark. If it’s a sunny day, the warmth from the sun can maintain the warmth in your home, so close your blinds early enough to capture this warm temperature so your appliances don’t need to work as hard.