It's hard to make good decisions on energy if you don't understand the jargon. It's really quite simple if you take the time to understand it. Here are a few of the most important terms:

Btu. The British thermal unit, a measure of heat-specifically, the amount of heat required to raise 1 pound of water 1 f. It takes about 100 million Btu to heat the average home for a season.

Btuh. Btu per hour, used to measure heat flow (e.g., out through a wall) or heat production (e.g., of a furnace or stove).

U. A measure of the amount of heat transmitted in 1 hour through 1 square foot of a building section (roof, wall or floor) for each 1 F. of difference between the warm and cold sides of that section. Expressed in Btuh. The lower the U, the better.

R. Resistance to heat flow, sometimes expressed 1-U. Insulation is labeled in R-values, and the higher the better. R-values are additive: If 31/2" of mineral-wool gives R-11, 7" will give R-22 and save twice as much heat. When you buy insulation, look for the highest R-value per dollar, which is more important than thickness.

Perm. A measure of the effectiveness of vapor barriers, a perm is equal to a gain (1/438th of an ounce) of water passing through a square foot of material per hour, per inch of mercury differecne in vapor pressure between the two sides of that material. The lower the perm value, the more resistance to vapor flow. Perms become important when insulation is blown or gunned into existing structures without vapor barriers. Water vapor will migrate outward and condense on cold surfaces, where it can cause rot and a host of other problems. To avoid this, you need a vapor barrier on the warm side of the new insulation. It should have a perm rating of about .25 or lower. The easier way to get this barrier is with a coat of a vapor-resistant paint. Ask for a paint rated .25 perms or less.