6. Block the unused chimney, then set the thermostat properly
An open, unused fireplace is the largest single hole left in most older homes — a permanent uncapped shaft from your living room to the sky, pulling warm air up it all day. A chimney balloon or a wool draft excluder costs $25 to $45, CA$35 to CA$65 or £20 to £35 and pushes up into the throat of the flue in two minutes. Leave the tag hanging down where you can see it, because if anyone ever lights a fire with the blocker in place you will have a room full of smoke within seconds. If the chimney serves a working appliance or a gas fire, do not block it at all.
Now that the envelope is tighter, reset the controls, because a sealed house holds heat long enough that your old schedule is wrong. Drop the thermostat by one degree Fahrenheit and live with it for a week before deciding — most households settle at 68°F or 20°C in living rooms and a few degrees cooler in bedrooms. UK households with a combi boiler should also check the flow temperature on the boiler display; many are shipped at 80°C when 55 to 60°C lets a condensing boiler actually condense, which is where its efficiency comes from. That single setting change costs nothing.
Turn down radiator valves in rooms nobody uses, but leave them at the frost setting rather than fully off, and keep the doors to those rooms shut so you are not heating them through the hallway. If you have a hot water cylinder, check it has a modern insulating jacket; an old thin one or none at all wastes heat around the clock.
Finally, reverse the ceiling fans to clockwise on low if you have them. That pushes the warm air that has collected at ceiling height back down the walls instead of blowing a cooling draft on you. Run it on the lowest speed only — anything faster defeats the point.
Do all six steps and a typical household sees a meaningful drop in the first full billing cycle, usually somewhere between 5 and 15 percent of heating spend depending on how leaky the place was to start with. Keep the receipts and compare the same month year over year rather than month to month, because weather swings will otherwise drown out the change.