I have the following situation:
1. 3 level split house 1800 sq feet in the Seattle area
2. In the last 8 two heat exchanger developed cracks .
3. 8 years ago I have hired a local heating contractor to install a new gas furnace and got Carrier install. I dont believe that salesperson did proper Manual-J sizing, but merely eye-balled the house, windows, etc to recommended proper sizing.
The installed furnace is:
Carrier 58RAV095, Input BTU 92000, 80% efficiency, therefore output BTU 74000.
It may worth mentioning that during its 8 years inducer motor was replaced 3 times (two while previous inducer motor was on its own warranty)
This is a second furnace with the crack, albeit a hairline crack.
According to the rough estimate http://www.hvacopcost.com/equipsize.html the correct BTU for my house would be 79000. So the my furnace seems to be within the range.
With all these said:
1. Would what would cause 2 cracked heat exchangers in the course of 8 years? According to above reference furnace does not seem to be oversized
2. Is there inherit problem with the Carrier 58RAV (keeping in mind 3 inducer motors which gone wrong)?
The house is build in 1969, where there is no obstructions in the ducts, some rooms on the 3rd level have pretty poor airflow. I would attribute this to lack of proper design (too many 90 degree bends).