HVAC / runnable MCP tool
Run the Manual J Residential Load Calculator (ACCA 8th Edition Form J1) in your AI assistant
Through the free Intry MCP server, Claude, ChatGPT, or Cursor runs this exact calculator and hands back a verdict and the cited source, not a guess. Tool name: manual_j_load.
How it computes the answer
Worked term by term through the ACCA Manual J 8th Edition abridged procedure, against the ASHRAE Handbook of Fundamentals 2021 Chapter 14 design conditions for the station you name, re-derived on every build.
What it cites
Your assistant calls the same engine the interactive calculator calls, with the inputs listed under Inputs. These are the sources that engine reads.
- ACCA Manual J, 8th Edition, Abridged Edition (MJ8AE), Form J1 and Form J1ae
- The procedure and the printed tables this engine reads: Table 2A infiltration, the Table 3 fenestration procedure with Table 3A-1 and the Table 3D peak solar factors, Tables 4A and 4B for opaque panels, the four printed Table 7 duct arrangements, and Figure 3-1 with Table 10 for internal gains. The composition is the printed one: Form J1 line 25 for the heating total, Form J1ae line 20 and line 21 for the sensible and latent cooling pair. The composition rule was re-derived against the manual's own worked Vatilo Residence form and reproduces both printed totals exactly. The abridged edition is a real limit rather than a shorthand: where Figure 3-5 marks a table Not Supported for MJ8AE, this tool refuses that term by name instead of borrowing the full edition's procedure.
- ASHRAE Handbook of Fundamentals 2021, Chapter 14, climatic design conditions
- The heating and cooling design dry bulbs and the coincident wet bulbs, read for the United States station block and used for the one station nearest your ZIP. The latent side reads no printed grains table: it derives the grains difference from those same design conditions, a substitute for Manual J Table 1A rather than a reading of it. Manual J supplies the procedure these temperatures feed; it is not where they come from. Each station was transcribed twice, independently, and the two transcriptions agree on every cell. Station coordinates were additionally checked against NOAA on the subset that check has been run over, which the interactive calculator's trace states by count. Nothing outside the Handbook confirms the temperatures themselves, so its printed table has the final say.
- US Census Bureau 2020 Gazetteer Files, ZIP Code Tabulation Areas (ZCTA5)
- How your ZIP becomes a place on a map, accessed 2026-08-08. The Census INTPTLAT / INTPTLONG internal point: a point guaranteed to lie inside the ZIP Code Tabulation Area. A ZCTA is a tabulation area built from census blocks to approximate a ZIP code, so this is neither the ZIP's geometric centre nor a postal address. Some ZIP codes have no ZCTA at all, including point codes and PO-box-only codes. A ZIP with no ZCTA is refused by name rather than mapped to a neighbouring area. The nearest station is then chosen from that point and the distance is published beside the answer, so a station that is a long way from you is visible rather than implied. If the nearest station is further from you than the widest gap inside the table itself, the calculation stops and says so. Inside that bar the distance is published rather than judged: station spacing is not a climate test, and a station 40 miles away across a ridge can be a different climate than one 200 miles away across flat ground.
The design temperatures are LOOKED UP from the ASHRAE Handbook for the station named on your result; the loads are COMPUTED from them by the Manual J worksheets, live, as you change an input. This follows the ABRIDGED Manual J procedure, MJ8AE, not the full 8th Edition, and the difference is scope rather than accuracy: several constructions, glass types, skylights, external sun screens and engineered ventilation are outside the abridged tables, and each one is refused by name on the result rather than approximated. It is not an ACCA-approved Manual J and does not replace a permit-grade calculation. The daily-range class is an answer YOU give, because Manual J prints it per station in Table 1A and that table is not transcribed here; the interactive calculator prints the definition beside its control and the class you pick changes the sensible total. The load is only ever as good as the house you described: this cannot see your building, and it takes your envelope answers at face value. The design temperatures are the Handbook's, and where the printed tables do not reach your site the answer is withheld rather than extrapolated. The equipment manufacturer's own data and the AHJ have final say.
The full receipt, with every source and how each is cross-checked, is on the interactive Manual J Residential Load Calculator.
Ask your assistant
The one rule that makes it reliable: name Intry in your question. That is what tells Claude to run the manual_j_load tool and answer with the real number, the verdict, and the citation. Leave Intry out and Claude may just guess from memory, which is exactly what you are trying to avoid. Type something like:
Inputs
| Field | Required | Accepts | What it is |
|---|---|---|---|
| state | yes | string | US state, spelled out as the ASHRAE Handbook prints it (e.g. 'California'). Used with `station` to select the weather station. |
| station | optional | string | The weather station name exactly as the ASHRAE Handbook prints it (e.g. 'ALAMEDA'). Case-insensitive. If you do not know it, call with `state` only and read the coverage answer. |
| conditionedFloorAreaSqft | yes | number | Conditioned floor area in square feet, e.g. 2000. |
| ceilingHeightFt | optional | number | Average ceiling height in feet, e.g. 8. Area times height is the above-grade volume Worksheet E needs. |
| bedrooms | yes | number | Bedroom count, e.g. 3. Manual J Figure 3-1 sets occupants = bedrooms plus one; that is the printed rule. |
| stories | optional | single, two | Storey count, a Worksheet E input. Manual J Table 5A prints single-story and two-story air change values only; a taller dwelling is outside the printed table and is refused rather than approximated. |
| tightness | optional | Tight, Semi-Tight, Average, Semi-Loose, Loose | Manual J Table 5A envelope tightness class. All five printed construction rows are accepted. |
| fireplaces | optional | number | Number of fireplaces, e.g. 0, a Worksheet E term. |
| applianceOptionBtuh | optional | 1200, 2400 | Manual J prints exactly two appliance block loads and this tool will not accept a third. Call without it to be told which two. |
| windowRoughOpeningSqft | optional | number | Total window ROUGH OPENING area in square feet, e.g. 240, not glass area. Table 2A and Table 3A-1 both use the rough opening; glass area understates every window by its frame. Omit or pass 0 for no glass. |
| windowExposure | optional | North, NE or NW, East or West, SE or SW, South | Table 3A-1 prints five compass groupings, not eight and not a bearing. Map a bearing yourself; this tool will not bucket one for you. |
| windowPanes | optional | single, double, triple | Manual J check list item 6 admits clear 1, 2 or 3 pane glass, which is exactly this enum, so the pane count alone cannot put a dwelling out of scope. What the glass is MADE of can, and that is windowGlassType. |
| windowGlassType | optional | clear, heat-absorbing, reflective, low-e | Required whenever windowRoughOpeningSqft is supplied, and deliberately not defaulted. Manual J check list item 6 admits clear glass only, and Figure 3-5 scopes the abridged edition's Table 2A to '(clear glass)' and its Table 3A to '(3A-1; clear glass)'. So heat-absorbing, reflective and low-e glass each end the calculation with that printed reason rather than being priced off the clear-glass table. Defaulting this to 'clear' would answer a check list item on the caller's behalf. |
| windowSash | optional | fixed, operable | Sash type. Table 2A prints different U-Values for each. |
| windowFrame | optional | Metal No Break, Metal with Break, Wood, Wood with Metal Clad or Vinyl, Insulated Fiberglass | One of Table 2A's four printed frame constructions. Refused rather than defaulted: on the widest row the four columns span 0.38 to 0.72. |
| windowInternalShade | optional | No Internal Shade, Vertical or Horizontal Blinds with Slats At 45 Degrees, Drape or Roller Shade Half Drawn, Drape or Roller Shade Fully Drawn | One of Table 3A-1's four printed internal shade states. |
Add Intry to Claude
One paste and Claude can run this tool and every other Intry calculator, right from your phone.
- Claude opens with the Intry connector already filled in. Review it and click Add.
- (If a field is blank, paste the link below into the URL field.)
- In any chat, tap + then Connectors and switch Intry on. Then name Intry in your question (“use Intry to…”) so Claude runs the tool instead of guessing.
https://www.intrysys.com/api/mcpNo login, no API key, and it works on every Claude plan, right from your phone.
Using ChatGPT, Cursor, or a dev tool? See the developer setup on the main page. The endpoint is https://www.intrysys.com/api/mcp.
Every answer comes with the ACCA Manual J 8th Edition Form J1 worksheet procedure and the ASHRAE Chapter 14 design conditions it was computed from, so you can check it or show an inspector. The numbers come from the same calculator we run on intrysys.com, and we re-check every one automatically before anything goes live, so the number Claude hands you matches the code.