Hello; Efficiency in terms of cost can depend on our long term plans. If you own the home and plan to be there for a time then insulation of the space will pay off. If you rent or do not plan to stay then more heaters may be the best short term solution.
Before I bought my current home I rented a house. The rental had a full unfinished basement where I kept several tanks. One side of the basement was for parking a car so had a garage door. Every time I opened the garage door heat was lost. I came up with a middling solution.
I attached tarps to block off the area around the tanks. I attached the tarps to floor joists and the center support beam.
Made a tarp door way with smaller tarps for access arranged so they overlapped. That way when I came and went the tarps would sort of lightly seal behind me.
The tarps were longer than the walls were high and when I opened the garage door they would move about and thus spill my trapped heat. Solved that by attaching long pipes and even 2x4's to the bottom of the tarp and rolling them up enough to just reach the floor. Metal fencing top rail pipe I had around did the better job as it was easy to match it to the needed length.
Turned out to be a fair solution. I could feel the difference in warmth when I went into the area holding my tanks. Did cut down on my heating bill and my tanks kept at a more steady temp.
There was a neat aspect to this arrangement in addition to being easy to remove when I moved out. That was I found I could just roll the tarps onto the pipes all the way up to the top and tie them in place with short ropes. That way in warm weather they were up out of the way and easy to roll back down the next fall.
