Always deal with wasp nests very cautiously. Wasps are likely to attack and sting if their home is moved improperly, and a wasp sting is very painful. If you are allergic to them, the stings can also be fatal and a nest is home to a large number of the insects. A wasp nest can sometimes find its way into an air duct because of the shelter and seclusion a duct provides. Remove the nest systematically to ensure no one is stung.
Wear thick layers of clothing that cover your entire body. Include gloves, a veil and goggles to help protect against being stung. Keep all clothing tucked in to eliminate any openings that a wasp can fit into.
Spray the nest with a wasp pesticide at night. Avoid spraying during the day when the wasps are likely to be more aggressive. Use a sprayer that allows you to target the nest from at least 10 feet away. Stay as far back as possible when spraying the nest.
Sprinkle a pesticide dust around the nest to affect any remaining wasps and kill wasps returning to the nest.
Observe the nest for a day to ensure it is not still active.
Spray the wasp nest once more while wearing all of your protective clothing and then pull it out of the duct if you can reach it. Throw it away. Wasps will not reuse an old nest so it should not attract new wasps. You need to remove it though so it won't attract other pests.
Do not shine a flashlight on the wasp nest since this will aggravate the wasps. If you need a light source while spraying at night, place a red filter on the flashlight. Do not attempt this with beehives since they normally have many more bees than there are wasps in a nest. If you cannot access the nest in the vent directly, have it professionally treated.
Do not damage the nest itself in any way when spraying it since the wasps are likely to scatter if the nest is breached. Do not attempt this if you have any kind of allergy to wasp or bee stings. Have the nest professionally removed.