hang on . . . . Do you have an air compressor or portable air tank ?
I posted this elsewhere and copied/pasted it here.
Yesterday, I went up stairs to find some hornets in the upstairs window, killed them only to more more in another room. Luckily I found a spot where they chewed through the drywall tape in the corner of my daughters bedroom. I found they were coming in through one of the gable end vents, like 10-12 at a time
I made a trip to town and bought some Sevin dust. I took a piece of brake line and duct taped it to an air nozzle, filled it with Sevin dust and blew it into the vent, three different times.
Result, didn't get stung and the hornets are dead today. There's not a one flying in or out.