I have used and seen people using a blow torch, I do not recommend this method. As Karl had mentioned it is extremely dangerous. It only takes one small ember to drop somewhere unseen and several hours later Poof. I have seen it happen and if the home owner is around they may have a stroke or heart attack seeing you torching their home.
I also Recommend using a heat gun. As Karl mentioned it has more then enough heat to remove the paint whether it be one layer or 50 layers.
The easiest way to use it is to heat a small area use a putty knife to scrape the paint off. You can also spray a bit of water on it which will create a bit of steam and help loosen the paint.
Using a paint remover is probably the quickest way to complete the job. Although I have always been fearful that using these products, tend to seep into the would and when your scraping to start to remove part of the wood along with the paint. So if you do go this route be sure to not gouge the wood. Yes I realize you are a contractor and have done this work for many years, I am simply giving a heads up, not trying to talk down. So you don't make some of the mistakes I had made, years ago when I first started out in the Painting and Construction Trade.