HVAC / runnable MCP tool

Run the A2L Refrigerant Charge Limit Calculator 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: a2l_charge_limit.

Add it to your assistant Open the interactive calculator

What it runs: The maximum A2L refrigerant charge (R-454B, R-32, and 6 more) for a room, or the minimum room area for a given charge, per UL 60335-2-40 4th ed Annex GG and ANSI/ASHRAE 15.2-2024. m_max = min(AF x 2.5 x LFL^1.25 x h x sqrt(A), 0.5 x LFL x h x A, 52 x LFL); at or below m1 = 6 x LFL there is no room-size restriction. Set direction to 'max-charge' (give the room area) or 'min-area' (give the system charge). Circulation (continuous or refrigerant-detection-initiated) doubles ONLY the gravity term (airflow factor AF = 2). Returns the limit, the governing term, the m1/m2 thresholds, and the release height used. A3 refrigerants (e.g. R-290 propane) are excluded: the Annex GG room-area formula does not apply to them. SCOPE: this tool sizes ONE space per call and takes no list of spaces. On a multi-head system ANSI/ASHRAE 15.2-2024 section 9.4.1 makes the space with the SMALLEST DISPERSAL VOLUME (floor area x dispersal height) govern the whole system, which is not always the smallest room by area, so call it once per space and take the smallest answer rather than assuming the obvious room governs. This is an HVAC compliance tool; authority is UL 60335-2-40 and ANSI/ASHRAE 15.2-2024, never the NEC. It is a sanity check; the equipment listing and the manufacturer's installation manual are the binding documents.

Ask your assistant

The one rule that makes it reliable: name Intry in your question. That is what tells Claude to run the a2l_charge_limit 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:

“Use Intry for the maximum R-454B charge in a 200 sq ft room with a ceiling cassette.”

“Ask Intry the minimum room area for a 6 lb R-454B ducted system with the supply register at 9 ft.”

Inputs

Field	Required	What it is
refrigerant	yes	Refrigerant id, e.g. 'r-454b' or 'r-32'.
direction	optional	'max-charge' = biggest charge for a room (give areaFt2); 'min-area' = smallest room for a charge (give chargeLb). Default max-charge.
mounting	optional	Indoor-unit release-height class: floor (0.6 m), window (1.0 m), wall (1.8 m), ceiling/cassette/supply register (2.2 m), or custom (with heightFt). Default wall (the more conservative common height).
areaFt2	optional	Floor area in ft2 of the ONE space this call sizes (max-charge direction). This tool answers for a single space and takes no list of spaces. On a system with more than one indoor unit, ANSI/ASHRAE 15.2-2024 section 9.4.1 makes the governing space the one with the smallest dispersal VOLUME, which section 9.4 defines as floor area multiplied by dispersal height, so the smallest room by AREA is not always the one that governs: a larger room with a lower indoor unit can be the binding one. Where the units sit at different heights, call this tool once per space and take the smallest result, or use the web calculator, which takes the whole system. Default 150.
chargeLb	optional	System refrigerant charge in lb, nameplate plus field-added for line-set length (min-area direction). Default 6.
heightFt	optional	Release height in ft when mounting = 'custom' (clamped to 2.0 to 9.0 ft per ANSI/ASHRAE 15.2-2024 Table 9-3 footnote a). Default 7.2.
circulation	optional	Continuous or RDS-initiated air circulation (AF = 2, doubles only the gravity term). Default false.

Add Intry to Claude

One paste and Claude can run this tool and every other Intry calculator, right from your phone.

Add Intry to ClaudeOpens Claude with Intry already filled in.

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/mcp

No 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 UL 60335-2-40 and ANSI/ASHRAE 15.2-2024 standards it came 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.

Also on Intry

A2L Refrigerant Charge Limit Calculator (interactive)

The same engine as a hands-on calculator, with the full readout, chart, and worked examples.

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