Insulation Investment Calculator

Have you ever invested money in the stock market, or put money into an interest bearing bank account? If so, you were interested in the rate of return on your investment. Spending money on insulating your house is also an investment. It's return is in consistently lower utility bills to heat and cool your house.

Insulation resists the flow of heat. Knowing the R values before and after an insulation upgrade and the average temperature difference across the insulation, you can calculate the amount that the insulation upgrade reduces heat flow. Knowing the cost of energy and the cost of the insulation upgrade, you can calculate the rate of return on your investment in insulation.

This interactive calculator does these calculations for you, letting you quickly and easily investigate the cost-effectiveness of various insulation upgrades.

Inputs
Old R value		Added R value
Area	(Square Feet)	Cost of Insulation	$
Climate
Heating Degree Days (*)		Cooling Degree Days (*)
Energy Cost
Natural Gas	$per Therm	Electricity	$per Kilowatt Hour
Heating / Cooling System
Type of Heat:
Heating COP (*)		Cooling COP (*)
Calculated Energy Savings
Energy Saved per Year	BTU = KWH
$$ Saved per year	$	Return on Investment	% per year

Don't be surprised at a fairly large rate of return, especially if your house is poorly insulated, you live in a severe climate, have an inefficient heating or cooling unit, or expensive fuel.

Bear in mind that this calculates monetary rate of return. The savings of energy is also environmentally beneficial, reducing a variety of pollutants, and conserving finite fossil fuel supplies.

(*) Notes:

COP stands for "Coefficient of Performance". It is a non dimensional representation of the efficiency of a cooling or heating system, as is EER, which has the units of BTUH/Watt. To convert EER to COP, multiply it by 0.293.
Heating Degree Days and Cooling Degree Days, or HDD/CDD. These are tracked by the Weather Service, and represent the number of days that the outside temperature is cooler or warmer than some assumed inside temperature, multiplied by the temperature difference. It is common for HDD and CDD to both be calculated against an inside temperature of 65F, which is a little colder than most indoor spaces in winter, and much cooler in the summer. It is appropriate when using this calculator to increase the HDD a little, and decrease the CDD by quite a lot, depending on local climate.

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