heating

As mentioned before, our energy needs can be broken down according to category. From our table of electrical usage for the Peak Oil Homestead, we can extract the following:

Heating
Furnace: 300W, 8 h/day --> 4 kWh/day
Water: 4500W, 6 h/day --> 27 kWh/day

Cooling
Air conditioner: 600W, 8 h/day --> 4.8 kWh/day
Deep freezer: 600W, 12 h/day --> 7.2 kWh/day
Refrigerator: 600W, 8 h/day --> 4.8 kWh/day

Cooking
Oven: 5000W, 3 h/week --> 2.1 kWh/day

In the last post we discussed the common industry insulation measure known as the R-value. Focusing solely on a material’s R-value can be a major mistake, however.

First, R-values are determined under very specific laboratory conditions: in a warm, dry, wind-free environment. Of course, every home is subject to wind and precipitation, and even protected layers of insulation will be affected by weather. Fiberglass insulation loses nearly all of its thermal properties when wet, and allows air to flow through it easily even when dry.

An often-mentioned number in home building is “R-value” or “R factor”. The R-value is a measure of a material’s resistance to heat transfer and is used to compare different types of insulation. It is calculated using the thermal conductivity constant, k:

R = [thickness (in inches)] / k
k = [BTU * inch]/[ft^2 * hours * ?F]

Insulation must be treated as a whole-structure concept. Just as the amount of insulation in your home means little if you leave your door wide open, using very high-R material in the walls may provide little return if you use low-R windows. It’s all in the rate of heat transfer.