Unless that room is in active use, heating it and/or air conditioning it costs an enormous amount of money and energy.
Here's how to isolate that room (as much as is possible) from the rest of the house so your furnace or A/C unit isn't spending extra energy controlling the temperature there.
Step 1: Materials
You will need:
Several towels - the number depends on the size of the room and its specifications. Also, these don't need to be your finest monogrammed bathtowels, just anything you can dig up.
Duct tape (possibly) - This depends whether or not things will stay on their own where you want them.
Step 2: Block Off the Windows
The windows I'm demonstrating here are double layer storm window-style ones. I realise that many, are just a single sliding layer of glass. That will change things slightly (cue the duct tape!).
First, close the exterior pane if you have double windows, or just close the whole thing if it is single.
For a double layer of glass, stuff towels in there until the entire space between has been filled. The tape shouldn't be necessary, as the towels (the photo actually shows old hoodies) should be wedged in their firmly enough on their own. Then close the interior window and close the blinds.
For a single window, you'll have to break out the ol' duct tape to keep the towels attached to the window.
As a final note, I would recommend the use of black or darkly coloured towels for this, as it will be the least obtrusive when viewed from the outside.
Step 3: Seal the Vents
First, most vents will have some kind of switch that will close the vent. When you close them, you may notice that there is still some air getting through.
For vents along the baseboard, toss a towel over it, but make sure that it covers the whole vent. If it won't stay, keep fighting it for as long as your patience will allow. If you really, REALLY have to, use the tape, but I would advise against it. There's a fair chance the tape will damage any paint on the wall or vent.
Not that the previous step was very difficult, but floor vents are even easier. Simply close the vent, then toss over a towel.
Step 4: Stop Draughts (drafts)
To accomplish this, lay a towel flat on the floor in the bottom of the doorway.
Next, fold it back on itself. Be careful to make sure any bumps or creases are flattened out, else the door will catch on them.
Finally, close the door, and make sure any towel poking out is made even with the door so that no one trips and breaks their neck on it.
Step 5: Final
- Don't leave any lights on in your newly insulated and mostly empty room.
- Don't forget any pets inside - they won't be pleased.
- This is only meant for infrequently used rooms that can be adequately closed off from the rest of the house.
Hopefully, this 'ible will save you some money, and the Earth some wasted energy.