I set the Nest thermostat to 75 but the house is always like 60-68 degrees. I put my hands on the vents and the air is not warm at all. How do I verify that my furnace works? The blower is working but I'm not sure about the heating. [attach]110534[/attach]

so our home has a Janitrol (Goodman) gas furnace. the first 7 years, we had zero problems with it. but the past 3 years, i have had issues every year. the first problem required replacing the circuit board and igniter. when the (silicone carbide) igniter goes bad, it takes so many amps that it burns the board up. i learned this the hard way, by replacing 2 circuit boards. initially, i replaced the igniter because i broke it getting it out. the 2nd year, when the board burned up, i also checked the igniter, and that was the eureka moment. the igniter had gone from 50 ohms, to over 200 ohms of resistance in just 1 year. so this year, i checked the igniter before heating season began, and the igniter had gone up to 140 ohms resistance. so i replaced it, in hopes that i will not have to replace another board. i would like to change this entire ignition system to a style that uses a "spark plug type" if that is possible. my initial thought was to just get a spark igniter, and graft in an ignition coil from a small motorcycle to run it. but knowing how dangerous "custom cobbling" can be, i figured i had better find a better way. any ideas?