My 80% efficient furnace was made in 1969. It does not have a crack as of yet. It still has the original blower motor. I have cleaned the system almost every year and inspected it for a cracked heat exchanger. My outside condenser has a hole on the backside where rust has eaten about 15 sqin of metal. This unit was replaced in 1984. It has never had any parts replaced. I guess that it is luck of the draw. (I also modified the system for efficient operations in 1995)

With this said, I believe many systems do not survive more than 12-15 years. Many condenser coils may only last about 5 years.

I have decided to replace my 21 year-old 7 SEER Trane heat pump even though it is still working. This decision goes against my normal logic which is to run things into the ground unless maintenance costs become too much. The reason for the replacement is that Maryland electric rates are going up 65%, and I can save 45% in energy costs with a 14 SEER unit, so my net increase in the electric bill is 20%. If rates were not going up, I would keep my 21 year-old unit and have window units as a back-up in case the heat pump failed in the summer.

i just replaced a 30 year old system with a brand new heat pump 2 weeks or so ago. it was working fine for heat and during mild days for cooling, but could not keep up with demand on days above 85 or so and that is MOST days around here. when we pulled it out, the housing for the coil was rusted thru and had a hole in it the size of a softball. this hole was NOT there last summer, as i seald all ducts myself and checked for air leaks along 100% of the system. our best guess is that once i sealed the leaks the pressure caused the rust to give way and blow a hole thru it. i could have just replaced the housing and gotten away with it for a while, but i decided to go ahead and replace the entire system and save some money on my electric bill at the same time.

my other system, for the rear of my house, is 12 years old and works extremely well. i am hoping it will last at least until i get the new one paid for, and then it too will be replaced.

I think most systems outlast their SEER ratings - That is, it's probably more economical to change them before they quit just to get the energy savings a new one will give you

Been there, done that twice already - Swapped out a 7 SEER for a 10 in 1994 and swapped the 10 for a 14 last year

Don

I don't think there is any sure way of telling how old a system gets before it needs replacing. There is for when you "should" though.
It's time when the system is just to expensive to operate or maintain and no longer is trustworthy.
I've seen old noisey, rusty, ugly systems that I thought would die anytime, run another 5 years or so- amazing! But then I've seen systems I thought would last many more years go out sooner than normal.
Older systems can last last 30 years, the later systems seem to average 12-18 years. Competition for price and efficiency has driven makers to use thinner copper and materials, though compressors are much better now than years past with the scroll technology.
A good proffessional installation is utmost important if the life of the system is a concern along with yearly service.
The time to replace a system is BEFORE it goes out completely and is in the age range of 12-18 years.Some sooner.
If you don't trust your HVAC company to deal honestly with you, then you need to shop around, but remember- picking the company that tells you what you want to hear, may not be the right choice either.

This is great reply from other people.

Life expectancy of an Hvac system depend on location and regular maintenance.

I had seen air conditioner that last for 30 and still running fine with few parts replace.

I also had seen unit that only last for 5 years. I would blame that unit. I would rather blame the contractor on that.

Here is a link that might be useful: central air conditioning units

Our old SEER 10 A/C system was beginning to cost serious money in repairs, located on a Gulf front condo in Florida. I replaced the complete system in May 2001 with a new Trane SEER 14 unit (including the air handler). Our property manager gave me a hard time saying it was physically "too large" although the compressor is roof top mounted. My air-conditioning/heating costs were cut in half.

During the last 24 months we have spent slightly over $1000 in repairs. I believe I am now at the point of diminishing returns with my 10-year old SEER 14 Trane unit. I am thinking of getting a SEER 16 system (BUT IT WILL NOT BE A TRANE UNIT DUE TO THEIR EXTRAORDINARILY HIGH REPLACEMENT AIR PART SELLING PRICES TO CONSUMERS WHICH IS AKIN TO HIGHWAY ROBBERY).

I

My two Carrier furnaces were 25 years old when I replaced them two years ago. The only repairs I did was the control board. One of the condensers required a new fan. The other was never repaired. I did no maintenance except change the filters.

A 16 year old furnace is not old, but the condenser is reaching the end of life and not worth repairing.

No one can predict when you will have a failure. You have the luxury of doing your homework on a replacement system. The best times are between the hot and cold temperature extremes when HVAC contractors are not busy.

I have 2 lennox AC & electric furnaces systems in my house that were installed in 1971. Still running (knock-on-wood) have had to replace relays and 2 fan motors over the 40 years. One unit is a 5 ton and the other is a 2 ton with a combined total of 45kw of electric heat strips....a real energy hog to say the least!

to the previous poster with 7 tons of cooling and 45kw of electric strip heating. I bet your bills are quite high. You should consider upgrading your 7 tons of cooling to heatpumps that are the highest efficiency single stage. I'm sure those 1971 compressors can't be higher than 8 seer or maybe even lower. You will save tons of energy on the cooling side and even more on the heating side. Heatpumps produce heat in-expensively and today's heatpumps are more reliable and long lasting than ever. What climate are you in? What do you pay for electricity per KW hour (total rate with delivery and taxes).

Thanks neohioheatpump, yes these are about 6.8 seer and the time has come to replace them. I am going to replace them with Goodman 13 seer Heatpumps w/r410. I know there are higher seer units but I prefer simplicity. I used to be a an HVAC contractor so that is the reason they have been able to survive this long. Even with the 13 seer and heatpump the reduction in operating costs should be tremendous. Both these unit are slightly oversized because we zone them. Neither run at the same time as one is for the bedroom area and the other for the main living area. Whenever we leave the house for more than a few hours we turn the units off and ,this may explain why they have lasted for 40 years. With a heatpump this strategy may not be needed but I plan to try both methods. From a cold start the electric will supplement the heatpump for about an hour. Since the main unit will be operating during the daytime the outside temps will normally be above freezing
which will increase the efficiency of the heatpump cycle.

I agree, simple things do last longer. You might want to consider upgrading to the highest eff. single stage. That is typically 14 seer outdoor unit and turns to 15 seer with the air-handler.

I also am against setbacks with heatpumps much because they work best at maintaining temperatures. They have a tendency to run a long time to bring temperature backup unless you run auxiliary.

What is your climate? What type of electric bills do you currently have with heating with electric resistance without heatpumps? You want to maximize the heatpump run time and minimize electric resistance heat time. I would consider a brand heatpump that has demand defrost. THis is a nice feature that is available on some heatpumps and will surely save wear-and-tear of unnecessary defrosts and energy. Rheem/Ruud, York-Luxaire-Colemand, American-std/Trane all have demand defrost.

Thanks for the reply neihioheatpump. My climate is in the southeast=outside design temp of 92 & 10. When house was built it was built as a "gold medallion"by the utility,at that time they were pushing all electric homes and giving you a lower utility rate...they would even pay for the service entry riser and panel! My Kw usage has been as high as 7800. The rate here is 11.5 cents (the all electric discount was dropped long ago). I will have to due some calculating to see if less expensive to maintain or setback. I plan on installing enough resistance heat to satisfy my heat loss,that way I will have emergency heat if needed. I will probably add some outdoor thermostats to stage the Kw with the outside temps. I know, I have been putting this off for far too long.