Gas/Liquid Temperature Interaction is unusually slow

I'm not sure if this is intended but gasses seem to have a hard time transferring their heat to liquids or something I'm inherently doing wrong.

And this was a design I was using to heat up water and I did reach gas heat around 200C at one point (somehow) and yet water in the area wouldn't heat up as fast as I'd expected. It'd float around it's 40-50's it was and slowly climb but not as fast as I would expect. Occasionally, if I got lucky, steam would spontaneously be created but not as aggressive as I'd expect.