How efficient is a 20 year old furnace?

Related questions

1. Is a SEER rating of 16 good?
2. How long do Lennox air conditioners last?
3. How long do HVAC systems last?
4. What is the best rated furnace and air conditioner?
5. How many square feet does a 2 ton AC cool?
6. What is the minimum SEER rating for new systems?
7. How much does HVAC cost for new construction?
8. How many square feet will a 10 ton AC unit cool?
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Tags

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2. #utilization
3. #energy
4. #efficiency
5. #department
6. #furnaces
7. #roughly
8. #average
9. #annual
10. #furnace
11. #efficient
12. #according