They can have hot breath while having a regular body temperature. Flint starters or a pilot light in their mouth combined with a high fiber diet and the right microbiome solve this problem.

The only question left is how to move the flammable gases to the mouth. Maybe they have sacs they have to fill with roughage in their mouth. Maybe the only barrier in their digestive system is at the end so eau de colon just constantly seeps out.

Short stories and flash fiction avoid this problem by having genre conventions that allow for focusing only on a specific scene. Ploughshares in its recent Winter edition has a fiction piece that’s three paragraphs long, which I thought was an appropriate length for the content.

I think it’s somewhat common for writers to start with writing shorter pieces. GRRM comes to mind.