Just curious on the brands most installed, and how many old one's are still out there.
70% pilot driven
80% spark or Hot surface Ignitor, open burner type with or without ventor motor
90%+, sealed burner with secondary heat exchanger, plastic pipe vented usually.
Octopus fossil from the 1900s
I'm still running a early 80s Addison Weather King 70% I upgraded to 80% with a Robert Shaw 712-017 ICU kit. Very reliable, heats the house quickly,[probably too quickly to be efficient, to many BTUs] quiet and very standard parts found almost anywhere. I've over ran the blower wheel a bit for a bit more air flow thru a HEPA type filter and set the fan switch temp wise using the last run temp at 80F. Bills run $60-$100 a month for heat and hot water in winter. [gas usage+transportation pipeline fees+meter fee, all included]