Installed August 23, 2024 · Cross Mountain West, Fredericksburg, TX 78624
Short answer. For this 1,984 sq ft Fredericksburg home, the right size was 4 tons, not 5. Our certified heat load calculation found a 40,975 BTU/h cooling load and 3.52 tons of required capacity, so we replaced the oversized 5-ton R-22 unit with a 4-ton Carrier Infinity 26 Greenspeed variable-speed AC rated 44,000 BTU/h and 21 SEER2.
Key facts
| Item | Details |
|---|---|
| Location | Cross Mountain West, Fredericksburg, TX 78624 |
| Home | 1,984 sq ft, built 2004; furnace and coil in the attic |
| Old system | Payne PA13NR060 5-ton AC (R-22, made 2013, 11 years old), Day & Night N80ESN0902120A gas furnace (made 2020), ADP coil. Running, but not keeping up |
| Heat load result | Variable-speed load (certified heat load calculation, whole-home block load): cooling 40,975 BTU/h (37,978 sensible, 2,997 latent, calculated SHR 0.93); required capacity 42,198 BTU/h or 3.52 tons at 0.9 SHR for variable speed; 1,407 CFM; heating 25,697 BTU/h. Single-stage load: 41,835 BTU/h cooling; 51,250 BTU/h (4.27 tons) at 0.75 SHR; 1,708 CFM |
| Supply airflow | About 1,210 CFM from 13 supply runs before; about 1,595 CFM from 15 runs after adding one 9" and one 8" supply run |
| Return airflow | About 1,000 CFM from a single 16" return before; about 1,700 CFM after adding a 14" return |
| New system | 4-ton Carrier Infinity 26 Greenspeed variable-speed AC, Carrier Infinity 80 gas furnace, Carrier cased coil, Infinity System Control |
| Rated efficiency | 21 SEER2, 12 EER2, 44,000 BTU/h (AHRI 213687483); furnace 80% AFUE |
| Installed price | $17,066.70 ($17,415.00 estimate less a $348.30 discount for financing through GoodLeap) |
| Install time | One day, August 23, 2024, installed by Frank and Rey under Nathan Peterson, install manager at the time |
The problem: a 5-ton system that still was not comfortable
When our tech surveyed the home on August 8, 2024, the system was running but the house was not comfortable. The survey notes list:
- Warm rooms. "2 rooms stay warmer than the rest." The two back bedrooms "don't get as much air flow."
- Noise. The outdoor unit "makes loud rumbling noise frequently throughout the day."
- Ducts. Some ducts were "slightly kinked," and the house had a single return.
- Sizing. The outdoor unit was 5 tons, which the tech noted was oversized for 1,984 sq ft. The homeowner wrote: "5 ton now but my house is only 1984 sq."
- Drain. The primary drain was backed up, with water in the secondary pan.
The homeowner wanted a quiet system.
What the homeowner wanted, and the result
| What the homeowner wanted | What we did | Result |
|---|---|---|
| A quiet system, replacing an outdoor unit that made a loud rumbling noise | Installed a Carrier Infinity 26 Greenspeed variable-speed system | The homeowner's review calls it "Super quiet." |
| Open to two-stage or variable-speed equipment | Chose variable speed, rated 21 SEER2 | A 4-ton variable-speed system matched to the heat load |
| Fix the two back bedrooms that stayed warmer | Added a 9" and an 8" supply run to those bedrooms, plus a 14" return | The homeowner tells us the back bedrooms are comfortable now |
| Right size for a 1,984 sq ft house, after an oversized 5-ton unit | Sized from the certified heat load calculation | A right-sized 4-ton system, one ton smaller than before |
How the heat load set the size
We ran two certified heat load calculations on this home. One was calculated for a single-stage system, using a 0.75 sensible heat ratio: a 41,835 BTU/h cooling load and 51,250 BTU/h, or 4.27 tons, of required capacity, with 1,708 CFM of airflow. The other was calculated for a variable-speed system in a certified heat load calculation as a whole-home block load: 1,984 sq ft on a slab, 105°F outdoor and 74°F indoor in summer, 45°F outdoor and 72°F indoor in winter, 10% duct loss and gain, and a 0.9 sensible heat ratio for variable-speed equipment. The cooling load is 40,975 BTU/h (37,978 sensible, 2,997 latent, a calculated SHR of 0.93), and the required capacity is 42,198 BTU/h, or 3.52 tons, with 1,407 CFM of airflow. The heating load is 25,697 BTU/h. Glass is the largest part of the cooling load at 17,261 BTU/h (42%). The 4-ton Greenspeed, rated 44,000 BTU/h, is about 7% over the load, so it is properly sized. This was one system serving the whole house.
Why 4 tons and not 5. A 5-ton system would have been way oversized for this house, the ductwork would have had to be replaced to carry 5 tons of airflow, and a 5-ton system would not have managed humidity well. A 4-ton variable-speed system was the better fit.
The ducts were the other half of the job. The tech rated the existing return at about 2.5 tons of airflow and the supply at about 3 tons, short of what a 4-ton system needs, which matches the warm back bedrooms.
Supply and return ducts before and after
Our supply airflow takeoff from the duct diagram shows the original 13 supply runs carried about 1,210 CFM, short of the 1,407 CFM the variable-speed heat load calls for. We added two supply runs, one 9" and one 8", which brings the supply to about 1,595 CFM.
| Supply run size | CFM per run | Before | After |
|---|---|---|---|
| 4" | 20 | 5 runs (100 CFM) | 5 runs (100 CFM) |
| 6" | 75 | 1 run (75 CFM) | 1 run (75 CFM) |
| 7" | 110 | 3 runs (330 CFM) | 3 runs (330 CFM) |
| 8" | 160 | 3 runs (480 CFM) | 4 runs (640 CFM) |
| 9" | 225 | 1 run (225 CFM) | 2 runs (450 CFM) |
| Total | 13 runs, about 1,210 CFM | 15 runs, about 1,595 CFM |
The return side was short too. Our return takeoff shows the original single 16" return carried about 1,000 CFM, short of the 1,407 CFM the variable-speed load calls for. We added a 14" return, which brings the return to about 1,700 CFM.
| Return size | CFM per return | Before | After |
|---|---|---|---|
| 16" | 1,000 | 1 return (1,000 CFM) | 1 return (1,000 CFM) |
| 14" | 700 | None | 1 return (700 CFM) |
| Total | about 1,000 CFM | about 1,700 CFM |
What was installed
We quoted three options: a 2-stage system, a 5-stage system and the Infinity Greenspeed variable-speed system. The homeowner chose the Greenspeed system. Along with the equipment, the job added a custom return plenum and a new 14" return run, a supply plenum modification, and two new supply runs (9" and 8").
| Part | Old | New |
|---|---|---|
| Outdoor unit | Payne PA13NR060, 5 tons, R-22, made July 2013 | Carrier Infinity 26 24VNA648A003, 4 tons, variable speed, R-410A, made July 2023 |
| Indoor coil | ADP CT9460-M245AP, R-22 | Carrier CVPMA4921XMC cased coil, 4 tons |
| Furnace | Day & Night N80ESN0902120A, 88,000 BTU/h input, made 2020 | Carrier Infinity 80 58TN0B090C21--20, two stage, variable speed blower |
| Thermostat | Existing thermostat | Carrier Infinity System Control SYSTXCCITC01-B |
| Air quality | None | REME HALO in-duct air purifier, included at no cost |
Carrier lists the 24VNA6 compressor range as 25 to 100% of capacity and rates the 4-ton size at 53 dBA at minimum cooling speed (24VNA6 product data). The same document says the system requires an Infinity control with Greenspeed capability, so a third-party thermostat cannot run its variable-speed features.
How the install went
The crew installed the system and the duct changes in one day on August 23, 2024, from 8:19 AM to 6:02 PM. Installed by Frank and Rey under Nathan Peterson, install manager at the time. The install crew was Carrier Infinity trained. Atlas AC Repair is a Carrier Factory Authorized Dealer, and the system was installed under Texas ACR license TACLA00015901C (Class A), held at the time by Nathan Peterson.
Technical data
| Reading | Value | Source |
|---|---|---|
| Refrigerant (R-410A) gauges | Suction 140.6 psig (48.8°F saturation), liquid 369.8 psig (110.5°F saturation) | Install day gauge photo |
| Superheat / subcooling | 9.9°F / 8.8°F on the gauges; 10°F / 9°F on the form | Gauge photo and install completion form |
| Air temperatures | 82.8°F return, 60.3°F supply, about a 22°F split | Install completion form photos |
| Blower setting | High cooling 1,400 CFM, low 1,300 CFM | Install completion form photo |
| Static pressure (airflow test) | 0.47 in. w.c. at 1,417 CFM, blower 922 RPM; within the 0.3 to 0.8 in. w.c. range Carrier technical support and Carrier's training give for the Infinity airflow test | Confirmed on a tech follow-up visit, April 14, 2025 (thermostat airflow test photo) |
| Nitrogen pressure test | 400 psi, held 30 minutes | Condenser install form |
| Evacuation | Vacuumed below 500 microns | Condenser install form |
Estimated cooling savings
The old Payne PA13NR060 is rated 13.00 SEER (Payne spec sheet), or 12.35 SEER2 at RESNET's 0.95 conversion for ducted split systems (RESNET Addendum 71i). The new system is rated 21 SEER2. We used 2,209 full load cooling hours for Texas climate zone 3 (Texas TRM 13.0, Vol. 2, Table 29) and the Texas average residential electric rate of 15.91 cents per kWh for August 2026 (EIA Electric Power Monthly, Table 5.6.A). The old unit is figured at its actual 5 tons and the new one at 4 tons, so the estimate counts both the higher efficiency and the right sized system.
| System | Tons | SEER2 | kWh/yr |
|---|---|---|---|
| Old Payne PA13NR | 5 | 12.35 | 10,732 |
| New Carrier Infinity 26 | 4 | 21 | 5,049 |
| Estimated savings | 5,683 kWh, about $904 a year |
Math: kWh = tons × 12,000 × cooling hours ÷ (SEER2 × 1,000). Old: 5 × 12,000 × 2,209 ÷ (12.35 × 1,000) = 10,732 kWh. New: 4 × 12,000 × 2,209 ÷ (21 × 1,000) = 5,049 kWh. Savings 5,683 kWh × $0.1591 = $904. These are estimates from rated values, not measured use.
Cost and financing
The estimate was $17,415.00. We gave a $348.30 discount for financing through GoodLeap, for a final installed price of $17,066.70. It covered the Greenspeed system, furnace, coil and Infinity control, the return plenum, return run and two supply runs, the supply plenum modification, and a 10-year labor warranty. The REME HALO was included at no cost.
Warranty
Carrier registration lists 10-year parts coverage on the outdoor unit, coil and furnace through August 23, 2034, and furnace heat exchanger coverage through August 23, 2064. The 10-year labor warranty runs to August 23, 2034.
Maintenance plan visits
After the install, the homeowner joined our Annual Performance Agreement, a maintenance plan with two visits per year. Here is how the system has performed on those visits since the install.
April 11 and 14, 2025: a leak caught early. On the first Annual Performance Agreement visit, on April 11, 2025, the system was running well by most measures. The tech measured 58°F supply air and 72°F return air, the compressor drew 7.38 amps against a 14.6 amp rating, the drain line passed a gallon of water test, and the thermostat, low voltage wiring, filter and indoor unit all passed. But the low pressure line set was sweating heavily, so the tech flagged the compressor, refrigeration and condenser coil items on the condition report, noted a suspected leak and recommended a leak test.
On April 14, 2025, the tech came back, found a bad Schrader valve on the low side, replaced it and leak checked it with bubbles. Because everything was under warranty, we fixed it before it became a real problem down the road, at $0 cost to the homeowner. The thermostat's airflow test on that visit showed 0.47 in. w.c. static pressure at 1,417 CFM, with the blower at 922 RPM (confirmed on a tech follow-up visit). That is within the 0.3 to 0.8 in. w.c. range Carrier technical support and Carrier's training give for the Infinity airflow test.
November 14, 2025. Every item on the condition report passed. Superheat was 12°F and subcooling 6°F, with pressures of 121 and 277 psig. Supply air was 57°F and return 74°F, a 17 degree split. Those numbers differ from install day, when the house was 82°F inside and the system was under a heavy load. On a cool November day the system isn't working hard, so readings run differently. This visit was to confirm the April Schrader valve fix held for the long term, and it did. The compressor drew 6.3 amps against its 14.6 amp rating. The tech cycled the system in cooling and tested heat.
June 23, 2026. The tech flushed the drain line and checked the blower motor, the Infinity thermostat and the outdoor unit, and found the system running properly. The gauges read 292.0 psig on the high side.
The next visit is scheduled for December 23, 2026.
What the homeowner said
"Atlas AC worked with us from start to finish. Pete put all the gear in motion , made it happen. we bought the Infinity Greenspeed 21Seer2 4 ton . Super quiet. Frank and Ray were very informative and explain the unit very well. They took their time which I appreciate very much. You won’t go wrong with these guys they know what they are doing , no rush job, informative, trustworthy. Everyone did a wonderful job thank you AC Altas. Thank you Pete , Thank you for all the workers that made all this possible."
T, Cross Mountain West, Fredericksburg, TX 78624 · 5-star Google review, August 23, 2024. Quoted word for word.
Related pages
- Summerfield, San Antonio case study: replacing a working R-22 system with a 4-ton Carrier Infinity
- Carrier Infinity cost with installation
- HVAC replacement cost guide
- Air conditioning contractor in San Antonio
- All Atlas AC Repair case studies
Common questions
What size AC do I need for a 2,000 sq ft house?
Square footage alone isn't enough; a certified heat load calculation decides. This 1,984 sq ft house needed 4 tons, about 496 sq ft per ton, and its old 5-ton unit was oversized. Our certified heat load calculation for variable-speed equipment (whole-home block load, 105°F outdoor and 74°F indoor summer design) shows a 40,975 BTU/h cooling load and 42,198 BTU/h, or 3.52 tons, of required capacity at a 0.9 sensible heat ratio for variable-speed equipment. We installed 4 tons.
Is my AC oversized?
A certified heat load calculation is how to tell. Here the old outdoor unit was 5 tons, and the survey tech noted it was oversized for 1,984 sq ft. The calculation shows a 40,975 BTU/h cooling load and 3.52 tons of required capacity, so the system went down to 4 tons. The homeowner had also reported two back bedrooms that stayed warmer and a loud, rumbling outdoor unit.
Why not 5 tons?
A 5-ton system would have been way oversized for this house. The report's 51,250 BTU/h (4.27 tons) required capacity figure was calculated with a 0.75 sensible heat ratio, which applies to single-stage equipment. The variable-speed calculation shows a 40,975 BTU/h total load with a calculated sensible heat ratio of 0.93, and the variable-speed Greenspeed system, rated 44,000 BTU/h, covers that load. The ductwork would have had to be replaced for 5 tons, and a 5-ton system would not have managed humidity well. The existing ducts were already short for 4 tons (about 2.5 tons of return and 3 tons of supply airflow), so we added return and supply runs sized for the 4-ton system.
Can an oversized AC cause humidity problems?
In Kenneth's judgment for this house, yes: a 5-ton system would not have managed humidity well, which is one reason we chose 4 tons instead of putting 5 tons back in.
What ductwork changes are needed going from 5 tons to 4 tons?
In this house the existing ducts were short even for 4 tons. The tech rated the return at about 2.5 tons of airflow and the supply at about 3 tons, so we added a custom return plenum, a new 14 inch return run, a supply plenum modification and two new supply runs (9 inch and 8 inch).
Why were two bedrooms warmer than the rest of the house?
The survey found the two back bedrooms did not get as much airflow. The ducts were undersized for the system (about 2.5 tons of return and 3 tons of supply), some ducts were slightly kinked, and the house had a single return. The new return and supply runs were added to address that airflow.
Did the added ducts fix the warm bedrooms?
Yes. We added a 9 inch and an 8 inch supply run to the two back bedrooms, plus a 14 inch return, and the homeowner tells us the back bedrooms are comfortable now.
Does window glass affect what size AC I need?
Yes. In this house glass was the largest single part of the cooling load: 17,261 BTU/h, or 42% of the 40,975 BTU/h total, according to the certified heat load calculation.
How has the system performed since the install?
On our Annual Performance Agreement visits it has kept passing. In November 2025 every item on the condition report passed, with 12°F superheat, 6°F subcooling and a 17 degree temperature split, and in June 2026 the tech found it running properly. In April 2025 a tech found and replaced a bad Schrader valve on the low side, and the airflow test on that visit showed 0.47 in. w.c. static pressure at 1,417 CFM.
How efficient is the new system?
The matched Carrier system is rated 21 SEER2 and 12 EER2 with 44,000 BTU/h of cooling capacity (AHRI 213687483). The old Payne unit was rated 13.00 SEER, about 12.35 SEER2.
How much did it cost?
The estimate was $17,415.00, and a $348.30 discount for financing through GoodLeap brought the final installed price to $17,066.70. That covered the Greenspeed system, furnace, coil and Infinity control, the duct changes and a 10-year labor warranty.
How much airflow did the ducts carry before and after?
Before, 13 supply runs carried about 1,210 CFM and a single 16 inch return carried about 1,000 CFM, both short of the 1,407 CFM the variable-speed heat load calls for. We added one 9 inch and one 8 inch supply run, bringing the supply to about 1,595 CFM, and a 14 inch return, bringing the return to about 1,700 CFM.
What does the maintenance plan catch?
Problems before they grow. On this system's first Annual Performance Agreement visit in April 2025, the tech saw the low pressure line set sweating heavily and suspected a leak. Three days later we found and replaced a bad Schrader valve on the low side. It was under warranty, so the fix cost the homeowner $0.
How long did the install take?
One day. The crew worked from 8:19 AM to 6:02 PM on August 23, 2024.
Proof and sources
- Atlas heat load reports: single-stage load (0.75 SHR) and variable-speed certified heat load calculation whole-home block load (0.9 SHR); survey notes; install completion forms and photos; invoice; Carrier registration.
- Carrier 24VNA6 product data; Carrier 58TN0 furnace page; Carrier 58TN0B product data; Carrier CVPMA product data.
- AHRI 213687483, Carrier AHRI ratings tool.
- Payne PA13NR spec sheet; RESNET Addendum 71i; Texas TRM 13.0 Vol. 2; EIA Table 5.6.A.
- TDLR license record for TACLA00015901C (Class A, issued October 30, 2002, expired July 25, 2025, business Atlas AC Repair LLC).; TDLR license search for TACLB00153401E, the license Atlas AC Repair now operates under.
