Leaky Ducts - How much energy are you losing?

Ductwork - One of the highest losses of energy I see when performing energy audits is leaky ducting. There are facts and formulae out there stating you could be losing as much as 20% of your heating energy costs due to leaky ducting. In my case, I find that the average is about 10%. So if your building has ductwork that runs either in your attic or crawlspace (or both!) and it's leaky, you can use this simple formula to determine how much those leaky ducts cost you:

If you have gas heating:

(Total \$ of heating fuel) - (Average of three lowest month's bills) x 12 x 1.1)) x 0.10 = Cost of duct losses

Example: (\$1000 - (average of June, July, and August (\$15) x 12 x 1.1)) x 0.10

(\$1000 - \$200) x 0.10 = \$80

(by calculating the average of your three lowest bills, you can determine what is used for water heating and cooking, if applicable)

If you have electric heating:

(Total \$ of electricity) - ((Average of three lowest month's bills) x 12 x 1.1) x 0.10 = Cost of duct losses

(the 1.1 multiplier accounts for the average variance for winter when more lighting will be used)

Example: (\$2500 - (average of May, June, and September (\$70) x 12 x 1.1)) x 0.10

(\$2500 - \$925) x 0.10 = \$158

Wouldn't you like to put that money in your pocket? Of course your mileage may vary, and I'm quite certain it will. So this example should only be used for very rough estimates. Of course you would tend to increase the 10% number to something like 20% or even more if you go down to your crawlspace and find that some of your ducts are just hanging out, not connected to anything. That'll certainly cost you a bunch on your utilities. It happens!

But what else does it cost you? Well for one, it costs your health. A good HVAC system should be a closed system, where the same amount of air that is blowing out of the supply registers is also being sucked into the HVAC system through return registers. The amount of intake area and return area (measured in square inches or square feet) should be the same but I rarely see them sized appropriately, perhaps 75% of the time, at best. With an unbalanced system, two things can occur:

In most cases, the fix is simple: flexible duct mastic over each and every duct joint. What's not simple is the labor. It's a miserable job crawling around in your crawlspace or attic, trust me, I know from experience. But it's absolutely necessary, I assure you. And if you don't want to do it yourself, hire a high-school kid or someone who needs the money, because, to be quite honest, it's not rocket science applying the mastic. What it takes is a person with a pulse and a willingness to get dirty for a while.