A/C vs system replace in ATL

MediaMogul2020

10 years ago

Tough situation here. Builder grade A/C unit failing- symptoms are small temp delta at registers and occasionally outside fan won't start and/or squeals.
The furnace is 13 yrs old and is basic single stage Comfortmaker model. 80% AFLUE I think. The a/c compressor replaced about 7 yrs ago. 2.5 ton unit. The outside fan motor was replaced only three years ago. I'm thinking the fan blades are vibrating and causing premature failure on the motor bearings.

House is basement and two floors. Basement has Lennox heatpump- works w/o issue.
Top Floor 2 ton Comfortmaker, original unit- no issues.

Main floor is the problem child.
The unit runs constantly in summer since we bought the house 3 yrs ago. Things improved somewhat when I found and fixed a 50% blocked 12" return. (blocked due to prior owner basement remodel-long story) In addition there are two more 8" returns. Sq footage of main floor is about 1700' with cathedral ceilings in family room and foyer. Otherwise 9' ceilings . The unit still runs constantly if temp exceeds low 80's outside. Obviously a sizing problem. No other known ductwork issues.

The usual scenario is that the A/C turns on in the morning and the inhouse temp gradually rises to about 81 and then falls to our preset of 77 at around 11pm. Unit shuts off.

So I am weighing a 3 ton compressor/coil replacement vs system replacement with something like a Carrier 16 seer with two stage furnace. My installer mentioned that I will not exceed roughly 14 seer if I keep the current furnace. If I keep the furnace I would probably opt for a Carrier Performance 13 seer a/c compressor/coil unit.

My big question revolves around the estimated lifespan of this comfortmaker furnace which has been running 100% duty cycle daytime hours in summer and 50% in winter. How long do heat exchangers typically last?

It is 13 years old. I should mention the furnace exhaust blower makes a loud pinging noise (bearings?) so it's nearly toast.

I lean to system replace but it's gonna be twice the cost and ROI is not good if we move in around five years. (Likely) $3.4k a/c only vs $7-8k for complete system.

Any thoughts welcome and sorry if this issue has been posed before-
Oh my wife and I much prefer gas over a heat pump.
We're located 25 miles north of Atlanta, GA.

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Comments (6)

tigerdunes
10 years ago
Has the AC always behaved this way in comfort or has this been a gradual worsening of not maintaining thermostat setting over the years. You may be undersized by a 1/2 ton.

What size is the furnace? Where is it located?

I would want to see a load calculation for cooling and heating for the main floor system..

This system was quoted for a Louisville location last week and included Infinity Controller and box filter cabinet. Price was $7.5 K. You should be able to come close to that price in Atlanta area.

6405563 Active Systems INFINITY 17 PURON AC CARRIER AIR CONDITIONING 24ANB736A**31 CNPV*3717AL*+UI 1050 840 58CV(A,X)070-12 36000 13.00 17.00 1 RCU-A-CB 256 Yes

70 K Infinity 80 furnace, Infinity 2 stage 3 ton condenser, matching ALA evap coil, qualifies for Fed Tax Credit.

You would want your ductwork for main floor totally inspected as to size both supply and return to handle extra cooling CFMs if you moved up to a 3 ton system.

Post back.

IMO

This post was edited by tigerdunes on Tue, Aug 27, 13 at 16:25
MediaMogul2020
Original Author
10 years ago
Thanks for chiming in.
The a/c performance has been consistently bad on the main floor.
When I unkinked the 12" return two years ago, the inside temp went from 83 or 84 to around 81 on a typical 90 degree summer day.

I will have to check the furnace BTUs when I get home.
It's located in a large louvered closet in the middle of our finished basement.
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MediaMogul2020
Original Author
10 years ago
Original furnace says 50,000 BTU/HR. I confirmed that it is 80% AFUE. Furnace keeps up just fine even at 20 degrees F outside.

Ok thanks for the spec'd Inifinity. I will have to get a quote for that whole system.

We have a quote for an Infinity 16 model 24ANB636A003 for the compressor and new coil model CAPMP36.

Came in at $4300 not inc the furnace.
With labor, equip pad, replacing fiberboard with Sheet metal plenum, and install (1) 8" return for the required CFM. Use existing line set.

Not sure why replacing the plenum- the old one has no mold and no air leaks. Plenty of surface area to add one more 8" return. There's room to add a couple more 8" returns if we wanted to.

The Carrier Performance 13 Model 24ACB336A003 came in at $3500. Seems pretty high for a nearly obsolete compressor/coil.
tigerdunes
10 years ago
Media

Just so you know, you can't pair that Infinity condenser with your conventional existing furnace and expect to achieve the performance that one would expect from that equipment. Waste of money.

IMO
MediaMogul2020
Original Author
10 years ago
Thanks Tigerdunes.

Yeah I only looked at the Infinity condensor as 1 possible option. The thinking is replace the compressor/coil now and then later when money is not so tight, add the matching Carrier furnace.
The tech mentioned that the coil would swap in easily enough without having to reconnect or evacuate the lines again.

But I am not loving the idea of breaking this down into two parts. Seems like the less we handle the coil, the better. Not to mention additional labor costs vs whole system replacement at once.

Here in the Southeast we have been having a very mild but wet summer. I think I might just hang on for 2 or 3 more weeks, save my pennies and re-evaluate in the spring.
If money/economy is still a problem, then I can decide to go with A/C components only.
The wife and kids have all been trained to bang on the outside fan housing to get it working on start up LOL.

The rebate situation is unclear- not sure if Carrier will extend it next month (Sept.) or not.

TigerDUnes you mentioned the Fed energy tax credit for the Infinity 17 system that you spec'd. What kind of $ savings and how does that work or can you give a link?

I emailed the Carrier rep yesterday to add whole system quote and revise the a/c quote to reflect keeping the fiberboard plenum and factor in the cash discount but have not heard back.

Thanks a "ton" for your voice in the middle of darkness.
tigerdunes
10 years ago
Fed Energy Tax Credit

Apprx $350 with the 80% eff var speed furnace and high eff AC

http://www.energystar.gov/index.cfm?c=tax_credits.tx_index

iMO

Here is a link that might be useful: Fed Tax Credit

This post was edited by tigerdunes on Wed, Aug 28, 13 at 11:37

A/C vs system replace in ATL

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