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Manual S Equipment Selection - ACCA-procedure right-sizing in 30 seconds.

Match Manual J loads to AHRI-certified equipment with sensible and latent capacity at your design conditions, using the sizing limits from the first edition of Manual S. Part of the Pro plan.

Worksheet / Manual S · #BS-2026-MS-0001 · Example project

Project2,000 sq ft single-family
LocationHouston, TX
Climate zoneIECC 2A · hot-humidASHRAE 169
DateMay 15, 2026
Prepared byBuildSolver

Design conditions

Outdoor DB (cooling)95 °FAHRI A-test ¹
Outdoor DB (heating)34 °FASHRAE 2021 · 99%
Indoor DB (cooling)75 °F
Indoor RH50 %

Manual J output - load from prior step

Total cooling load35,500 BTU/hMJ8 § 6.4
Sensible cooling25,000 BTU/h
Latent cooling10,500 BTU/h
Sensible heat ratio0.70
Total heating load24,000 BTU/hMJ8 § 7.5

ACCA Manual S - Equipment selection (Zone 2A · 115% cap)

Recommended unit3-ton heat pumpACCA MS
Rated capacity (47 °F)36,000 BTU/hAHRI H1
Total cooling @ 95 °F36,000 BTU/h
Equipment SHR (default)0.78
Sensible cooling @ 95 °F28,080 BTU/h
Latent cooling @ 95 °F7,920 BTU/h
Heating capacity @ 34 °F32,040 BTU/h
Balance point27 °F
Cooling load coverage36,000 ≥ 35,500 ✓ · ≤ 40,825 (115%) ✓
Sensible coverage28,080 ≥ 25,000 ✓
Latent coverage7,920 < 10,500 ✗ (2,580 short)
Heating coverage32,040 ≥ 24,000 ✓

Equipment · ACCA Manual S

3 tonheat pump(36,000 BTU/h @ 47 °F)

The latent check fails ✗, since the unit removes 7,920 BTU/h of moisture against a 10,500 BTU/h latent load, 2,580 short. No other size fits the window, so the calculator keeps this unit and points to a dedicated dehumidifier or a different evaporator coil for the gap.

+ Show your work

Cooling bin set (95 °F rating), which also sizes a heat pump: 18 · 24 · 30 · 36 · 42 · 48 · 60 kBTU/h

Cooling derate @ 95 °F (AHRI A-test rating point) = 1.000 total · 1.000 sensible · equipment SHR = 0.78 (default with no AHRI sensible rating entered)

Heating derate @ 34 °F (interp between 35 °F / 0.90 and 17 °F / 0.72) = 0.890

3-ton total = 36,000 × 1.000 = 36,000 ≥ 35,500 ✓ · ≤ 35,500 × 1.15 = 40,825 ✓

3-ton sensible = 36,000 × 0.78 × 1.000 = 28,080 ≥ 25,000 ✓

3-ton latent = 36,000 - 28,080 = 7,920 < 10,500 ✗ (2,580 short)

3-ton heating @ 34 °F = 36,000 × 0.890 = 32,040 ≥ 24,000 ✓ · balance point 27 °F, below the design day, so no backup heat at design

Next size down (2.5-ton / 30,000): total 30,000 < 35,500 ✗ - undersized on total.

Next size up (3.5-ton / 42,000): 42,000 > 40,825 (115% cap) ✗ - oversized total for cooling-dominated zone 2A.

With the matched coil's own sensible rating entered, this unit clears both the sensible and the latent line only if its sensible capacity at design lands between 25,000 and 25,500 BTU/h.

¹ Cooling outdoor 95 °F is the AHRI A-test rating point, used here for instructional clarity. Houston's 1% cooling design dry-bulb is 95 °F and its 99% heating design dry-bulb 34 °F in the BuildSolver dataset, within 1 °F of the ASHRAE 2021 values for Houston Intercontinental (KIAH).

These numbers come from the BuildSolver calculator. It holds the first-edition Manual S ceilings (115%, 125% for heat pumps in heating-dominant climates) and its own 100% floor, stricter than the 95% of the first edition and the 90% of Manual S-2023.

Calculate Manual S for your project

Pro plan · Whole-house loads stay free

01 · What is Manual S

Manual J gives you the load. Manual S gives you the equipment.

ACCA Manual S is the second half of correct residential HVAC sizing. After Manual J tells you the building needs, say, 35,500 BTU/h of cooling, Manual S forces you to verify that the specific condenser/coil combination you're going to install actually delivers that capacity at your real-world design conditions, not at the AHRI test conditions printed on the brochure.

That distinction matters because manufacturer nominal capacity is published at AHRI A-test (95 °F outdoor dry-bulb, 80 °F indoor dry-bulb, 67 °F indoor wet-bulb). At Phoenix's 108 °F 1% design dry-bulb, a 3-ton unit delivers about 2.8 tons. At a Denver elevation of 5,300 feet, thinner air cuts the coil's sensible capacity by about another 18%. BuildSolver applies that air-density derate where Census and USGS data pin down the job's ZIP elevation; otherwise the result states that no altitude correction was applied. At a Houston 95 °F design with 50% RH indoors, the sensible/latent split shifts in ways that catalog tonnage doesn't reveal. Manual S is the procedure that surfaces all of this before the install.

02 · Why Manual S after Manual J

Three checks Manual J doesn't make.

Manual J output is the input to Manual S. A Manual J that says "35,500 BTU/h" doesn't tell you whether a 3-ton or 3.5-ton unit is the right answer at your design conditions. Manual S forces three checks Manual J skips:

  1. Total capacity at design conditions.Read it from the manufacturer's expanded performance data. BuildSolver approximates it by applying an outdoor-DB derate (Cutler 2013 model, validated against expanded performance tables) to the AHRI-rated capacity. Manual S-2023 accepts 90% of the Manual J total load up to 115% for single-speed equipment (120% when the load is 24,000 BTU/h or less), 125% for two-speed and 130% for variable-capacity. The calculator holds the first-edition ceilings, 115% with 125% for heat pumps in heating-dominant climates, and its own 100% floor, stricter than the 95% of the first edition.
  2. Sensible capacity at design. Most catalog data hides the sensible/latent split. With no AHRI sensible rating entered, the calculator assumes an equipment SHR of 0.78, so a 36,000 BTU/h unit delivers about 28,080 BTU/h of sensible cooling at 95 °F and has 7,920 BTU/h left for moisture. Each half is checked against its own load, so a unit can match the total and still be flagged short on sensible or on latent.
  3. Heating capacity at design - for heat pumps. Heat-pump capacity drops as outdoor temperature falls. A 3-ton standard split heat pump rated at 36,000 BTU/h at 47 °F delivers about 32,040 BTU/h at 34 °F (Houston heating design) and only 29,160 BTU/h at 26 °F (Atlanta heating design). Manual S verifies the unit covers heating load at your specific heating design dry-bulb.

BuildSolver runs all three checks every time the select_hvac_equipment_manual_s tool fires. Each check is a separate line in the audit trail you can show your customer or a reviewing PE.

03 · Common oversizing mistakes

Three field mistakes Manual S would catch.

Rounding up to the next bin "to be safe"

Manual J says 35,500 BTU/h, contractor installs a 4-ton (48,000 BTU/h). That's 135% of load, above every Manual S-2023 cap, including 130% for variable-capacity equipment. Symptoms: short-cycle, poor humidity control in hot-humid climates, compressor failure 5-7 years earlier than expected. Energy Vanguard and Bryan Orr at HVAC School have published the post-mortems on hundreds of these installs.

Matching cooling tonnage to replaced unit

"The old one was 4-ton, so the new one is 4-ton." If the original was oversized 12 years ago, the replacement perpetuates the error and adds another 12 years of short-cycling. Manual S forces you to start from Manual J and set aside the nameplate of the unit you're replacing.

Ignoring sensible/latent split in hot-humid climates

Houston, Miami, Mobile, New Orleans - climates where latent load regularly hits 25-30% of total. A unit with high SHR (sensible capacity dominant) at design conditions removes heat but not moisture. The thermostat satisfies on temperature, the house sits at 65% indoor RH, and the homeowner calls back about mold within the first cooling season. Manual S sensible/latent check catches this before install.

04 · AHRI Coil Match-Up

Confirm the pair in the AHRI directory, then size from expanded data.

An AHRI-certified Coil Match-Up is a specific outdoor condenser paired with a specific indoor coil and tested as a combination. It shows the system is a properly matched set and gives you efficiency ratings you can compare. The same condenser with a larger coil delivers different total and sensible capacity, so confirm the Match-Up for the coil you will actually install.

The AHRI Certified Directory lives at ahridirectory.org. Search the condenser model and the directory returns every certified Match-Up with its AHRI reference number, rated total cooling at 95 °F, sensible cooling, SEER2, EER, and heating at 47 °F and 17 °F for heat pumps.

Capacity for the Manual S check comes from the manufacturer's expanded performance data at your design conditions, across outdoor temperature, indoor wet-bulb and airflow. ACCA and DOE Building America guidance both point to those tables for selection and to the AHRI certificate for the matched-system check. BuildSolver starts from the AHRI rating and approximates design-condition capacity with its derate model, validated within ±5% of expanded performance data between 85 °F and 115 °F. Check the manufacturer's table before you order.

05 · Sensible vs Latent

SHR is what separates good comfort from bad.

Sensible Heat Ratio (SHR) = sensible cooling load divided by total cooling load. A residential SHR of 0.70 means 70% of the cooling energy goes to dropping temperature, 30% to removing moisture. A warehouse with low occupancy and no cooking has SHR closer to 0.85; a kitchen-heavy household in Houston might drop to 0.65.

The industry rated SHR for single-stage residential AC at AHRI A-test conditions is 0.708 - a published value used in EnergyPlus, ResStock, and ASHRAE 90.1 reference models. BuildSolver uses that model (plus a 0.002 per °F adjustment for outdoor DB) to move sensible capacity with outdoor temperature. It starts from the AHRI sensible rating you enter, or from an equipment SHR of 0.78 when that field is blank.

Contractors get into trouble when they pick a unit whose total capacity covers Manual J total load and never ask how much moisture it removes. In our worked example above, the 3-ton unit delivers 28,080 BTU/h sensible at 95 °F (36,000 × 0.78) against a 25,000 BTU/h sensible load, so the sensible line passes. Its latent line fails: 7,920 BTU/h of moisture removal against a 10,500 BTU/h latent load, 2,580 short. A 3.5-ton unit is no way out, because 42,000 BTU/h is over the 40,825ceiling, and most of a bigger unit's extra capacity is sensible anyway. Close the gap with a dedicated dehumidifier or a coil and airflow match that runs a lower SHR, then enter that unit's sensible rating and run the check again.

Straight answers

Questions contractors ask about Manual S.

Do I need Manual S if I already did Manual J?
Yes. Manual J tells you the load. Manual S tells you which specific equipment will deliver that load at your design conditions, accounting for outdoor temperature derate, altitude, and the sensible/latent split. Skipping Manual S is the #1 cause of oversized residential HVAC - the contractor rounds up to the next tonnage to be safe, the unit short-cycles, and dehumidification suffers in hot-humid climates.
What is AHRI Coil Match-Up and why does it matter?
AHRI (Air-Conditioning, Heating, and Refrigeration Institute) certifies condenser/coil combinations through independent testing. Each certified pair gets a Match-Up reference number you can look up in the AHRI Directory at ahridirectory.org. The Match-Up proves the coil you install is rated with that condenser, which matters because catalog tonnage often corresponds to a different coil than the one installed in the field. For the Manual S capacity check itself, use the manufacturer's expanded performance data at your design conditions.
Why is my AC oversized and what happens?
Oversizing usually traces back to one of four causes: Manual J was skipped or done by rule-of-thumb (400 sq ft per ton); Manual J was done but Manual S was skipped, so the contractor rounded up; existing equipment was oversized and replacement matched the old size; total capacity matched the load but sensible capacity wasn't checked. The result is short cycling, poor dehumidification in hot-humid climates (mold risk), higher energy bills, compressor failure in 7-9 years instead of 12-15. The cost premium over the equipment's life is roughly $2,400 for picking 4-ton when 3-ton was correct.
How much oversizing does Manual S allow?
Manual S-2023 ties the cooling cap to the compressor. Single-speed equipment can go to 115% of the Manual J total cooling load, or 120% when the load is 24,000 BTU/h or less. Two-speed goes to 125% and variable-capacity to 130%. The floor is 90% of the total and sensible load and 100% of the latent load. The BuildSolver calculator still uses the ceilings of the first edition of Manual S, as ACCA summarized them in 2009: 115% of the cooling load, and 125% for heat pumps in heating-dominant climates, with its own floor at 100% of the load, stricter than the 95% of the first edition. For the calculator, heating-dominant means IECC zone 4 or colder. Houston (Zone 2A) gets 115%, and a heat pump in Minneapolis (Zone 6A) gets 125%.
Can BuildSolver replace Manual S for permit submission?
No. BuildSolver is sales-phase preliminary sizing. For permit submittal in jurisdictions requiring ACCA-approved software, use Wrightsoft Right-S or Cool Calc (both ACCA-approved). BuildSolver is what you use during the sales call to give a fast, defensible number to the customer with a citation-ready output. For the permit packet, the engineer of record uses ACCA-approved software.
What design conditions does BuildSolver use for derating?
When the site is one of the ten metro cities in its dataset, BuildSolver uses the ASHRAE 2021 station design values (1% cooling dry-bulb, 99% heating dry-bulb); for a ZIP code or any other location it uses an approximate estimate for the IECC climate zone, not location-specific. The cooling derate combines the Cutler 2013 biquadratic capacity model (industry-standard, used in EnergyPlus and ResStock) with a published rated-SHR model (0.708 at AHRI A-test conditions) that moves the sensible share with outdoor temperature. The sensible capacity it starts from is the AHRI sensible rating you enter, or an equipment SHR of 0.78 when you leave it blank. Heating derate uses NEEP CCASHP database 2024 averages for standard split heat pumps and cold-climate heat pumps separately.
How do I get AHRI-certified equipment data?
Look up your candidate condenser/coil pair in the AHRI Certified Directory at ahridirectory.org. Search by manufacturer model number. The directory returns the certified Match-Up reference, AHRI-rated total cooling at 95°F outdoor, sensible cooling, SEER2, and heating capacity at 47°F and 17°F for heat pumps. Enter those ratings in BuildSolver and it derates them to your design conditions. Before the final selection, check the manufacturer's expanded performance data for that pair.
What if my design outdoor temperature is above 115°F?
BuildSolver's derate tables are validated within ±5% of manufacturer expanded performance tables between 85°F and 115°F outdoor. Above 115°F (extreme Phoenix or Las Vegas summer design days), the validation residual rises to ±10%. We emit a warning above 115°F. For projects with design dry-bulb above 115°F we recommend cross-checking against manufacturer expanded performance data for the specific unit, because the biquadratic model loses accuracy in extreme heat.

Run Manual S on your next project.

Describe the job in a sentence. Get an ACCA-cited Manual S equipment recommendation with sensible/latent check at your design conditions. Manual S is part of the Pro plan; the whole-house load it starts from is free.

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Want the procedure itself before you run it? The walkthrough of how Manual S selection works covers the sizing limits by equipment type and four selections done by hand, two of which fail the check.

BuildSolver is not affiliated with ACCA · Manual S® is a trademark of ACCA