IMHO, a furnace tuneup is not a do-it-yourself job. You should be able
to measure blower static, gas pressure, manifold pressure, flame sensor
current, flue draft, stack temperature and few other things and
understand what they mean. If you want to do your furnace work, go to
www.darwinawards.com. If you don't know what you are doing, you are
risking damage or injury. Hire someone qualified and stay healthy.