The average lifespan of an air conditioning unit is around 15-20 years, while a furnace tends to last about 15-30 years. While this discrepancy in aging may lead you to believe that you should only replace one at a time, it isn’t always a good idea to piecemeal your HVAC system together. 

This guide will take you through the benefits and drawbacks to replacing your furnace and AC together and separately. 

Replacing Your Furnace and Air Conditioning System, At A Glance

You’ve probably heard the popular adage “if it ain’t broke, don’t fix it”. Why would you want to replace a machine that is working perfectly fine just because you have to replace another one?

You should consider replacing both your furnace and air conditioning unit at the same time if:

  • Your furnace is older than 15 years
  • Your air conditioning unit is older than 10 years
  • You’ve purchased an air conditioning unit with a SEER rating above 16.
  • You are looking for long-term savings on your energy bill
  • Your HVAC system is noisy (a symptom of mismatched systems)

Because the lifespan of an air conditioning unit is nearly half the lifespan of a furnace, it is more likely to be in need of replacement than the other. But even if your furnace is operating efficiently, it may also need to be replaced at the same time. 

This has to do with the underlying costs of mismatched systems, installation costs, and energy efficiency.

One Or The Other?

It goes without saying that replacing an air conditioning unit or a new furnace alone isn’t cheap. So why would you want to replace both at the same time? Won’t that double the cost? 

Surprisingly, no. Replacing a furnace on its own will run you between $2,000-5,000. If done along with an air conditioning unit, replacement costs tend to be much cheaper (between $1,000-3,000.)

Your furnace and AC unit work as a team, and need to be attached to one another in order to work. Air conditioning is mutually dependent on a furnace to operate, and will not cool your home as effectively without a furnace’s blower feature.

Another way to think about it is this: if you have a great internet connection but an old router, you’re not going to get a good Wi-Fi signal in your home. Like an internet router, there are ways to measure your AC unit to make sure you are getting the most bang for your buck—namely, the SEER rating.

Air Conditioning Unit SEER Ratings and Furnaces

SEER—or seasonal energy efficiency ratio—measures an AC’s efficiency. The higher the rating, the lower your cooling costs will be. However, in order to maximize savings, some things must be taken into consideration.

  • Pricing – The cost of air conditioning units tends to scale with SEER ratings, so the higher the SEER rating, the more expensive the unit.

  • Insulation – A well-insulated home will regulate both heating and cooling costs throughout the year. The money you save also depends on whether cool air is escaping your home.

  • Regulations – In 2006, the Department of Energy began requiring all air conditioning units to meet a minimum SEER rating of 13. In California, this minimum rating is set at 14. 

When installing a unit with a SEER rating above 16, a furnace replacement is typically advised. However, the balance between cooling savings and upfront cost is something that needs to be assessed. For this reason, experts recommend installing an AC unit rated between 15 and 18.

Tip: If your furnace and AC unit are not matched, your cooling costs will likely be higher, despite the unit’s SEER rating. It also may not cool your home at the intended level. Worse, a mismatched system can lead to premature failure, requiring more expensive maintenance over time.

Choosing to Replace Your AC and Furnace

Ultimately, the decision to replace either one or both parts of a furnace and air conditioner combination is yours. An AC system will still function if mismatched with a furnace, but may leave parts of your home warmer or cooler than others and will cost you more money over time.

You may not need to replace both your air conditioning and furnace systems at the same time if your furnace is less than ten years old, and is compatible with your new air conditioning unit. One way to think about replacing these systems is cyclically. Every other time you replace an air conditioning unit, you should consider replacing your furnace along with it. 

This can be challenging for new homeowners to determine if they don’t have access to that history, meaning the best way to determine this is through an inspection from trusted experts.

Simpson Sheet Metal is a leading HVAC company and provider of professional heating and air conditioning repair in Santa Rosa. Contact us today to learn more about how our technicians can help maintain and repair your furnace and air conditioning units.


Energy Star. When is it Time to Replace?

Bob Vila. What is a SEER Rating?.

Service Champions. Should I Replace My Air Conditioner and Furnace at the Same Time?