For HVAC contractors who quote fast

Manual J load calc + branded client PDF - in 90 seconds.

Built on ACCA Manual J procedures. Sonnet 4.6 orchestrates, deterministic code runs the numbers. Every result cites the table it came from.

  • ← This took 30 min in Excel
  • Cite-ready for client →
  • Branded PDF in one click →

Worksheet / Manual J · #BS-2026-0001

Project2,000 sqft single-story
LocationHouston, TX
Climate zoneIECC 2A · hot-humidASHRAE 169
Date2026-10-16
Prepared byBuildSolver

Design conditions - Houston KIAH

Outdoor DB (1% cooling)95 °FASHRAE 2021
Outdoor WB77 °FASHRAE 2021
Indoor DB75 °F
Indoor RH50 %
ΔT cooling20 °F

ACCA MJ8 · Table 4A - Sensible envelope loads

Walls (R-13, 1,141 ft² net)2,020 BTU/hMJ8 T.4A
Ceiling / attic (R-30, 2,000 ft²)1,870 BTU/hMJ8 T.4A
Windows (U-0.32, 250 ft²)1,600 BTU/hMJ8 T.3D
Doors (insulated, 40 ft²)320 BTU/hMJ8 T.4C
Slab floor (U-0.04)1,600 BTU/hMJ8 T.5A
Solar gain (SHGC 0.40, 250 ft²)7,750 BTU/hMJ8 T.3D
Infiltration (0.18 ACH)1,030 BTU/hMJ8 § A4-2
Internal (5 occupants + appliances)2,350 BTU/hMJ8 T.4A
Latent (infiltration + occupants)2,530 BTU/hMJ8 § A4-4

Cooling load · ACCA MJ8 § 6.4

21,100BTU/hr(2 ton)
+ Show your work
Sensible total18,540 BTU/h
Latent total2,530 BTU/h
Sensible heat ratio0.88
Recommended capacity21,100 BTU/hMJ8 § 6.4
Nominal tonnage2 ton
Equipment selectionManual S, separate stepACCA Manual S
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Worksheet legend

How to read this.

01

Header

Project name, address, climate zone, date. Same fields a senior engineer would write on the title block of a hand-drawn Manual J.

02

Tables & citations

Every row points at the ACCA table it came from. Tap the orange tag to see the section. No "trust me, the AI knows."

03

Stamp

BuildSolver is sales-grade. The orange stamp tells your AHJ this is preliminary — for permits, use Wrightsoft.

Calculators

Calculators by topic.

Single-purpose calculators for the numbers that come up on a job, each with the standard it works from. The on-page calculators need no signup.

All calculators with descriptions →

Tools, not guesses

HVAC, end to end. Canonical formulas. Cited tables.

Claude orchestrates the conversation. A library of deterministic calculators returns the number, the formula, and the citation. The math stays canonical; the AI only routes and explains. Design temperatures, IECC adoption, and licensing context are pre-loaded per state — see Manual J for Florida or Manual J for Arizona for hot-climate examples.

ACCA MJ8

Load calc

Residential cooling and heating loads with design conditions looked up for the site: ASHRAE 2021 station values when the site is one of 10 metro cities; an approximate IECC climate zone estimate for a ZIP code or any other location. Sensible / latent split per Manual J §6.

ACCA MS

Equipment selection

Air conditioners, heat pumps, furnaces, dual-fuel. Sensible / latent gating, balance point, aux heat. Manual S first-edition limits.

ACCA MD

Duct sizing

Trunk and branch sizing, friction-rate selection, total external static pressure check. Simplified for sales-phase quotes.

ASHRAE Fund

Psychrometrics

Wet/dry bulb, dew point, humidity ratio, enthalpy. Refrigerant-cycle and IAQ inputs from a single state-point call.

Behind the worksheet

The conversation that produced it.

BuildSolver asks the same clarifying questions a senior engineer would. Three messages from a sentence to a citation-ready load. The Houston example below uses the ASHRAE 2021 1% cooling design temperatures for Houston; Manual J for Texas lists the 0.4% values.

  1. >AC size for a 2,000 sqft single-story in Houston. Mid-80s build, slab, low-e double windows.

  2. BuildSolver

    Any envelope upgrades since construction — attic insulation topped up, air-sealing? On a house this age it moves the number half a ton.
  3. >Attic is R-30 now. About 250 sqft of glass total. No blower-door test on file.

  4. BuildSolver · 14 sec

    Total cooling load: 21,100 BTU/hr (≈ 2 ton). Sensible 18,540 / latent 2,530. Per ACCA Manual J § 6.4 — full breakdown in the worksheet above.

    Open in chat →

Speed delta

Excel: 30 minutes. BuildSolver: 90 seconds.

For permit submissions Wrightsoft is the right answer. For sales calls and client quotes, the math is the same and 30 minutes is too long.

StepExcel + WordBuildSolver
Setup time30–45 min90 sec
Climate-zone lookupLook up by handAuto from address
Citation of ACCA tablesIf you rememberAuto
Mobile on the truckPainfulFirst-class
Branded client PDFBuild in WordOne click
Permit-grade Manual JNoNo — use Wrightsoft

Common use cases

Where BuildSolver fits each job type.

Four guides covering the most common HVAC sizing scenarios. Each one walks through a concrete project example, comparison with the alternative tool, and FAQs.

Retrofit

Sized from a description — no blueprint required.

For replacement and upgrade jobs that never had original drawings. Describe what you see on site; get the Manual J.

Read →

Replacement

Brand-agnostic AC replacement sizing.

Same Manual J procedures as Carrier HAP, without the brand lock. Mobile-first.

Read →

New construction

Preliminary Manual J at design-development.

Numbers for framing decisions before drawings are stamped. Iterate as the spec firms up.

Read →

Permit

When does AHJ actually require a stamped Manual J?

Honest guide to the line between sales-phase sizing and permit-grade Manual J.

Read →

All guides →

Manual J by state

Load calc pages with local ASHRAE design temps.

State-specific Manual J pages with top-metro design temperatures, IECC adoption, and HVAC contractor licensing context already applied to the defaults.

View all states →

Guides & tools

The procedures behind the number.

Written for contractors who have to defend the sizing to a client or an inspector — worked examples, where the rules of thumb break, and which ACCA calculation decides what.

14 min read

Is a 250 Gas Meter Big Enough for a 24 kW Generac Generator

An AC-250 meter is rated 250 cfh at a 0.5 in. w.c. drop, and a 24 kW Generac Guardian burns 306 cfh at full load. Add up the house in cfh before you call.

13 min read

Normal AC Pressures by Outdoor Temperature for R-454B and R-410A

Lennox lists 336 psig liquid and 133 psig suction for its 3-ton EL16KC1-036 (R-454B, TXV) at 95°F outdoor. Read any gauge set against outdoor temperature.

15 min read

Does an AC Condensate Drain Need a Trap and How Deep

IMC 307.2.4 leaves the trap to the manufacturer. Goodman's AMST manual asks for a 2 in. drop and a 2.75 in. seal. Check it against the static at the pan.

9 min read

How to Estimate Furnace Gas Usage From Heating Load and Degree Days

Heat loss / design dT x 24 x HDD / AFUE / 100,000 gives therms. A 40,000 Btu/h Atlanta house comes to about 568 a year at 95% AFUE on a 65°F base, 296 at 57°F.

All articles →All calculators →Manual S equipment selection →

Straight answers

Questions careful contractors ask.

Is this permit-grade Manual J?
No. BuildSolver is sales-grade for preliminary sizing and client quotes. For permit submission to your AHJ, use ACCA-approved software such as Wrightsoft Right-J.
Which standards does BuildSolver follow?
ACCA Manual J 8th edition for residential loads, ACCA Manual S for equipment selection, ACCA Manual D for duct sizing, ASHRAE Fundamentals 2021 for psychrometrics. Each calculation cites the table or section it came from.
Can I trust the numbers?
The arithmetic runs in deterministic code, not the language model. The same canonical formulas your textbook uses. The AI orchestrates the conversation and explains the result; it does not invent values.
Can I put my logo on the PDF?
Yes, on the Pro and Team plans. Upload your logo, license number, and contact info once. Every quote PDF uses them.
What is free vs Pro?
Free gets you a daily limit of calculations so you can try the product. Pro at $29 per month (or $290 per year — two months free) adds branded PDFs, unlimited calculations, and saved project history. Team at $79 per month ($790 per year) adds shared workspaces.
What about electrical, structural, or plumbing?
BuildSolver is built around HVAC. The chat and the Manual J, S and D tools cover HVAC only. The free calculator pages also cover work that sits next to it: the breaker and wire for an AC, heat pump or mini split circuit, gas pipe and combustion air for a furnace, and tankless water heater sizing. Each page cites its standard and says what it does not cover. Structural design and general electrical or plumbing design are not covered.

Calculate your next quote in 90 seconds.

Describe the building. Get an ACCA-cited load and a branded client PDF. Free to try — no signup.

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