Replace A/C when replacing furnace?

I live in San Diego. House is 1600 sqft. My furnace is a 23 year old Day&Nite 80,000 BTU unit. It uses a 3 ton split system air conditioner, also 23 years old.
The A/c sees very little use and is working fine. The furnace is getting cranky and I would like to replace it.
Is it necessary or advisable to replace the a/c compressor and coil when I replace the furnace?
Is there any cogent need to replace even the coil? After all, there is no wear/tear on the coil. Can I just replace the pan under the coil when I replace the furnace?
I realize that a new A/c compressor and coil would be more efficient but we only use the a/c during an occasional hot spell, maybe 10 days a year.
--

Walter
The Happy Iconoclast www.rationality.net
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Walter E. wrote:

23 years old! Yea I would replace it. Considering where you are it may take a while to get your money back, but you are going to save a good percentage on the cost of running it. I suspect if you factor in the potential for breakdowns, and the expense and possible lack of available parts, you may actually be ahead a lot sooner.
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Joseph Meehan

26 + 6 = 1 It's Irish Math
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may
In stuff like this, labor is a big part of the installed cost. They are gonna have the whole thing apart and the a/c discharged anyway. Especially considering how small modern furnaces are- the HVAC guy would probably have to kludge up something complicated to make the old A/C properly fit onto the new furnace. Not to mention how to integrate it into the control system. Definitely, replace it all. Even if the payback in energy costs will be decades, most of the money should be recovered when OP or their heirs sell the house. A young furnace/AC is a big sales point.
aem sends...
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This is Turtle
By what you say --- I would change the furnace out and let it go. You only have one thing to change the A/C out for and that is failure and lost of A/C during the hot times. now with only 10 days or so as your failure time is cut way down.
TURTLE
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With 10 cooling days a years, you'll never see a payback replacing it early. If it ain't broke...
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I agree. If you used your AC a lot, the payback would be worth it. But with 10 days use a year the payback would be forever. I believe in selling high efficiency, but not if it doesn't save the customer money or improve their comfort. Wait till the AC Croaks, then replace the outdoor unit and indoor coil together for reliability and longevity. They are sold as matched sets and will work better if replaced together. The only other issue with a 23 year old indoor coil is they typically remove dirt from the air that the filter misses. This is because the coil makes a good filter when wet. The dirt gets caught inside the coil and affects air flow by blocking the spaces between the fins. If they check the coil when they replace the furnace, they will be able to tell you if it needs replacing. But with 10 days a year use, it will probably be OK.
Stretch
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If it were me, I'd replace the whole thing. At the very least, I'd get quotes on what the cost is to replace the whole thing now, versus what it will cost if you want it done seperately. I think you'll find it will cost considerably more to do it piece meal and at 23 yrs, you're on borrowed time. Also make sure to look into any rebates from the elec company that are frequently available.
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I'm sure by now you've read all the comments from everyone. I want to throw in my two cents worth....
As of January 2006, 13 SEER efficiency will be the law of the land for AC's. IF (caps intended) you don't replace it before then and it goes out after January 1, 2006, you'll have to pay considerably more for the 13 SEER equipment.
Your call.

also
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If I lived in San Diego and had your house I'd consider tossing the A/C and furnace and getting heat pump.
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HeatMan wrote:

Just a clarification: As of Jan. 2006 only 13 SEER or above can be MANUFACTURED, but anything manufactured before this date can still be sold. So, lower SEER equipment will still be available for awhile.
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I checked with three of my suppliers, Trane, Rheem, and Carrier say they are not going to overproduce for 2006. The cheaper brands I would expect it from. ICP, GMP, Nordyne, maybe even throw soem extra ones down the Payne assembly line. But the higher end manufacturers are looking forward to the higher SEER's; ME too! We don't sell anything below 13 SEER for the most part any way, although we did add-on to existing new coils 2 10's this week.
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Bob Pietrangelo
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My experience with replacing furnaces. Three years as an installer. It can be done, to save the indoor coil. They are often right on top of the furnace, so it's a bunch of extra work to do the "furnace only" replacement. It may actually be easier to replace the furnace and the indoor coil as a unit.
You can replace the outdoor unit (or not) at your leisure.
Of course, I can't see it from here. I'm going strictly by my experiences in Rochester, NY. Which might not be relevant in your area.
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Christopher A. Young
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Reasons to consider a new unit are, VS DC motors, 2 stage heat, the possibiltity you are oversized, the instalation of a superior larger size air filter, electric and gas savings in heat and cooling mode, future repairs, and utility costs are going up .
VS or variable speed can run on a Humidistat Thermostat offered by Carrier and Lennox and maybe others, that can be set to run at a very low fan speed to remove double the humidity on days when cooling is not the real issue but humidity is, this feature could lead to you using the AC much more than 10 days a year to lower just humidity with minimal cooling if that is an issue in your area. In heating mode you could run on low-fan, low fire for more even heat, and air circulation through the air filter. VS DC can take 2/3 to 1/2 the electric power of non VS DC for running the fan normaly and even less on low, 1/4 the power.
Your old units blower fan is probably much less efficient than any new unit and you will have electric savings in winter as well, but more with VS DC. VS DC are more prone to failure so a 10 yr warranty, normaly offered as an option would be necessary.
Get a load calculation in writing , from who ever you deal with, if your heat and AC are oversized now proper sizing will give better comfort winter and summer, especialy summer in humidity removal. To large an AC and you cool but remain clamy, to much Btu heat and a to big a blower and you heat to fast and uneven.
Humid areas realy need good humidity removal.
There are many good air filters out there that were not avalaible years ago, that not only filter better on first pass air but last longer due to their total size, so instead of monthly or so replacement it is yearly.
Electric and gas is not going down in price, with the proper unit sized and installed by a Pro new high effeciency equipment, and the deterioration your unit has you could save 50%-60% ++ on electric and gas in winter and 50- 80% ++ electric in summer on AC, and get more overall comfort and control in living.
There are so many comfort options offered today that did not exist years ago. At least look into them your options are endless.
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