CH4 + 2 O2 + heat = CO2 + 2 H2O

Great educational model on; High efficiency (or 90%, or condensing) furnacesuse a set of two heat exchangers in order to retrieve more heat from the combustion products than their mid-efficiency counterparts.
Enjoy.

Thanks Robert. Good stuff!

Thanks, Scott.

Thanks for the share Robert!

Always a pleasure, Junor.
You’re the best!