[cercis]

I would and have done so. But, I also put curtains over my windows first (except I would open the curtains if the sun was hitting that window).

I didn't have central heat, so I hung a blanket over the two doorways out of the main room (with the heater). We just lived in there. About an hour before bed, I'd turn on space heaters in the bedrooms to get them warmer.

I don't know how much it saved us, but I do know that that room was a lot warmer than the curtained off rooms. I could keep it 65-70 while the other rooms were much closer to the outside temps.

And, it doesn't have to be blankets. We had to paint a room in our house and needed to use spray paint (we had some exposed wallpaper or something which ran when it got wet, so we first sprayed spraypaint to coat it). We hung the very thin plastic over the archway into the room. Once again, it was a home without central heat and that room was one without a heater. It was sooo cold in there, just with that little thin plastic blocking the heat.