Will Adding Insulation to My Home Pay for Itself?
The amount of heat, measured in Btuh (British Thermal Units per Hour), that your home loses in the winter or gains in the summer is calculated by a formula that is multiplied by the temperature difference. The difference between the temperature of the outside air and the air inside your home. Therefore the larger the temperature difference the more heat that will flow through your walls and ceilings. And when the insulation is doubled, the heat flow is always cut in half. But at some point the heat flow is so small that cutting it in half does not make economic sense.
A Good Rule of Thumb...
Assuming your walls are insulated, you don’t want to tear them open to add more insulation, and if your compress the insulation by adding more, you are actually reducing the insulation value. Your ceiling is normally the easiest place to add insulation and because heat rises, it make sense to have a well-insulated ceiling. A good rule of thumb is that your ceiling joists should be covered. If you can see the joists (horizontal boards that the ceiling is attached to) you will save money by adding insulation and also filling any gaps. You should have at least 12 inches, but some ceilings have 20 inches or more.
For Example...
Let’s assume a 1,000 square feet of ceiling, an inside temperature of 70 degrees and an outside temperature of 20 degrees. If the ceiling has 5 inches of insulation (approximated an R18.5), the heat loss would be 2,702 Btu per hour or 64,864 Btu in 24 hours. Using my latest gas bill in Boulder, Colorado, the cost is about $0.48 to pay for the heat loss and keep the rooms at 70 degrees. Doubling the insulation to 10 inches would cut the heat loss and the cost in half. Over a year, especially if you have air conditioning in the summer, it make sense to double the depth of the insulation. The expense of adding 5+ inches of insulation would cut you comparative cost to less than a quarter.
Doubling the insulation again to 20 inches (adding an additional 10 inches) would cut the cost in half again, but economically this probably doesn’t make much sense.
Adding insulation to an attic or over the ceiling is a day job that is easy for a homeowner to do on their own saving the cost of labor. But the job must be done correctly to realize a savings in heat loss. A topic I will cover in my next blog.