Dew point is the tempurature the air cannot hold the weight of the water in it. The water then begins to condense and form droplets. This tempurature is always below or equal to the air tempurature.
Propane prices. Maine (ME) propane users spent an average of $2.724 per gallon over the 2012-2013 heating season. This is slightly higher than the 2.436 average for the country as a whole, for the reasons explained above (distance from major supply source, colder climate, higher demand).
Let's assume a home requires 80 million BTUs of heat per year and is heated using a furnace with an AFUE of 90 percent. Here, propane cost equals ($1.87/92,700) x (80,000,000/0.90), or 0.00002017 x 88,888,889. In this example, annual propane heating costs would be approximately $1,793.