have a 2300 Sf house w/27 yr old rheem gas heater that has an electric ignitor. however,turned on the heater, it blow up very hard w/ gas smell. called a technician and he said it has a delay ignition and/or valve problem. however, he cleaned the ignition switch and the burner and the problem was eliminated for a week till it happened again. we got two estimate for the unit change. For a 5 ton carrierw/ 16seer is $4998.00 and the other is $3998 including installation, what would be the BTU. would like to know if the unit and the prices are right and size up. if I like to change the heater for now and how much would it be for the same carrier system, and what is the difference bet one stage and two stage blower. Thanks