Dan P wrote:
I have a spare bedroom that has 3 registers. The room never gets used.
Although the vents do close, there is some leakage out of them. With
winter coming, I was thinking about using magnetic covers to save
energy. Is there enough air coming through these vents to make a
difference? See link below.

http://www.cetsolar.com/ventcover.htm

Also, when I bought my place last year, it did not have AC. I replaced
the gas furnace and had central air installed. The two bedrooms are on
the upper level. I have a high air return register in the hallway
between the bedrooms. I have another air return register on the main
level of my home, plus one in the finished basement right by the
furnace. Due to high ceilings in the bedrooms upstairs, it takes a lot
of heated air to heat the upstairs. Would it be wise, when I start
using the furnace, to cover the air return register upstairs until warm
weather returns?

Thanks!

Hi,
It is not a good idea to make a room too cold or hot even if unoccupied.
Air circulation is balanced and messing with it too much may create an
unexpected problem. I have 2 story house with 2 zone heat/ac which is
much easier to maintain even temp. hot or cold. Our NG is government
subsidized when the price goes over trigger point in winter. My
electricity is 7 cents/kwh locked in for next 5 years.