A weedwand (blowtorch on a stick) can work very well as long as you don't point it at one bit for long - it's more of a waving about action. Cobwebs tend to create a bit of excitement too as they go up with a woosh. I must admit that every time I do a henhouse with the weed wand I wonder if this time the whole thing will burn
We use a mixture of approaches - the weedwand (repeated every day for a week or so if there are red mites present, to deal with their reproductive cycle time), creosote substitute inside and out, diatomaceous earth (readily available locally under trade names) to the sheds and to the hens. We have three henhouses but not so many hens, so we intend to give one house at a time a really thorough going over then leave it empty for a couple of weeks to dry before we do the next ones. Our sheds are garden sheds converted to suit the hens, made with lapped planks, so we are careful to get right into the cracks, and to take out the perches and frazzle any mites there with extra care

We have had better success since we started treating the birds too - I used to believe 'the word' that the mites stay off the hens in the day, but it's not true
Unfortunately they will always come back