Flow Pack

Room by room heat loss, boiler and heat pump size

size_heat_source

Read-onlyIdempotent

Works out the heat loss of each room (fabric U x A x delta T plus ventilation 0.33 x air changes x volume x delta T) and the total, then sizes a combi, system or regular boiler, or a heat pump, to the nearest common size. Combi sizing also checks the hot water load (flow x temperature rise). Give each room's type, size and its walls, windows, roof and floor with U values, or construction presets for indicative values. Returns per-room losses with every element's working, the total, the size, status (indicative when presets were used), must_check and sources. Typical call: {"heat_source":"heat_pump","outside_design_temp_c":-3,"rooms":[{"name":"Lounge","type":"living","floor_area_m2":20,"elements":[{"type":"wall","area_m2":7.8,"construction":"cavity_wall_unfilled"},{"type":"window","area_m2":1.8,"construction":"double_glazed_old"}]}]}.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "rooms": "<rooms>"
    },
    "name": "size_heat_source"
  }
}

Input Schema

Name	Required	Description
`rooms`	Yes	Up to 40 rooms.
`trade`	No	Optional. The plumber or heating engineer's own business details (Nero Trade Profile v1, the same shape as Spark Pack and Nero Work). Used to prefill records and to give a stable nero_trade_ref. Not stored by Flow Pack.
`heat_source`	No	Default combi_boiler.
`reheat_hours`	No	Wanted reheat time. Default 1.
`margin_percent`	No	Added to the heating load. Default 10 for boilers, 0 for heat pumps.
`cylinder_litres`	No	System or regular boiler: cylinder size. Default 150.
`hot_water_priority`	No	Default true (reheat load not added).
`hot_water_flow_l_min`	No	Combi: wanted hot water flow. Default 12.
`hot_water_temp_rise_c`	No	Combi: temperature rise. Default 35.
`outside_design_temp_c`	No	Local outside design temperature. Default -3.

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 13, 2026

TDQS

A4.4/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already establish read-only, idempotent, non-destructive behavior, but the description adds substantive context beyond them: results include each element's working, a status of 'indicative' when presets were used, must_check items and sources. That caveat about preset-derived results is genuinely useful for interpreting output, though permissions or limits are not discussed.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The first sentence front-loads the core computation and sizing outcome, with formula details and the example call following. It is dense but every sentence carries information; the inline JSON example is long but earns its place given the nested room/element structure.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a tool with 10 parameters, nested room and element objects and no output schema, the description covers inputs, the calculation method, the return contents (per-room losses with working, total, size, status, must_check, sources) and a working example call. Nothing an agent needs to invoke it correctly appears missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3; the description earns above that by explaining how combi sizing couples the hot water load (flow x temperature rise) to the sizing decision and by tying construction presets to the indicative status flag. The remaining parameter defaults are already documented in the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description names specific verbs and resources: computing room-by-room heat loss (fabric and ventilation) and sizing a combi, system, regular boiler or heat pump. The resource is unmistakably distinct from sizing siblings such as size_radiators and size_pipe, and it even states the calculation basis and rounding rule (nearest common size).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It clearly says what to supply - each room's type, size and elements with U values, or construction presets when real values are unknown - and gives a complete typical call. It stops short of naming alternatives or exclusions (e.g. when to size radiators instead), so it is clear context without routing guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

All Flow Pack tools Inspect

Try in Browser

One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

Glama MCP Gateway

Add one secure layer between your agents and this server.