# HVAC Coil Load Calculator

> HVAC Coil Load Calculator is a paid API for AI agents from x402-agent-api.onrender.com, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-10).

Calculates sensible, latent, and total HVAC coil loads (BTU/MBH/tons), SHR, and condensate from airflow and entering/leaving air states, with full ASHRAE psychrometric step-by-step workings.

## Facts

- Endpoint: POST https://x402-agent-api.onrender.com/api/v1/hvac-coil-load?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-10
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/hvac-coil-load-calculator-e4ba3784
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_UgkwliVQcy98arg0XbOgX

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability hvac-coil-load-calculator-e4ba3784 -d '<json body>'
```

Example prompt: Calculate the cooling coil loads for an air handler moving 10,000 CFM at sea level — the air enters at 80°F dry bulb and 67°F wet bulb, and leaves at 55°F dry bulb and 54°F wet bulb. Give me the sensible, latent, and total load in MBH, the tons of cooling, the SHR, and how much condensate it produces, showing all the ASHRAE psychrometric steps.

## When to prefer this

Choose this endpoint when you need rigorous ASHRAE-compliant psychrometric coil load calculations with full step-by-step workings, support for both IP and SI units, elevation correction, condensate calculation, outdoor/return air mixing, or reverse-solving (finding leaving conditions from known loads). Prefer over manual calculations or generic psychrometric tools when you need tons, SHR, condensate, and a complete audit trail of every equation used. Use sibling psychrometric endpoint for single-state property lookups without coil load context.

## Known failure modes

- Fewer than two psychrometric properties provided for entering or leaving state — returns validation error
- Physically impossible air state (e.g. wet bulb above dry bulb) — returns error
- Airflow of zero or negative — rejected by schema
- Missing both leaving state and loads when trying to solve — ambiguous input error
- Elevation out of range (-1500 to 30000 ft) — validation error
- Conflicting or overdetermined inputs — may return note or error
- Network timeout from Render cold start — retry after a few seconds

## How this service works

HVAC coil load calculator: from airflow and entering/leaving air (any two properties each), the sensible, latent and total load, tons, SHR and condensate; or one state plus loads to solve the other. Outdoor/return air mixing and outdoor air % back-calculation. ASHRAE psychrometrics, elevation, IP or SI. Shows every step with the numbers. $0.002 USDC per call.

## Output

Returns a JSON object with the resolved entering and leaving air psychrometric states (dry bulb, wet bulb, dew point, RH, humidity ratio, enthalpy, grains, density, specific volume, vapor pressure), coil loads object (sensible, latent, total in MBH or kW, tons, SHR, total from enthalpy), condensate rate, atmospheric pressure, elevation, mode, units, unit labels, step-by-step ASHRAE calculation array with references, any notes, and suggested next tool calls.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "mode": {
   "enum": [
    "cooling",
    "heating"
   ],
   "type": "string",
   "description": "When solving a state from loads: cooling (default) removes heat, heating adds it. Detected automatically when both states are given."
  },
  "units": {
   "enum": [
    "IP",
    "SI"
   ],
   "type": "string",
   "default": "IP",
   "description": "\"IP\" (°F, CFM, in, BTU) or \"SI\" (°C, L/s, mm, kW). Default IP. Applies to inputs and results."
  },
  "airflow": {
   "type": "number",
   "description": "Total airflow through the coil: CFM (IP) or L/s (SI).",
   "exclusiveMinimum": 0
  },
  "leaving": {
   "type": "object",
   "properties": {
    "grains": {
     "type": "number",
     "minimum": 0
    },
    "dry_bulb": {
     "type": "number"
    },
    "enthalpy": {
     "type": "number"
    },
    "wet_bulb": {
     "type": "number"
    },
    "dew_point": {
     "type": "number"
    },
    "humidity_ratio": {
     "type": "number",
     "minimum": 0
    },
    "relative_humidity": {
     "type": "number",
     "maximum": 100,
     "minimum": 0
    }
   },
   "description": "Air leaving the coil: two properties, like `entering`.",
   "additionalProperties": false
  },
  "entering": {
   "type": "object",
   "properties": {
    "grains": {
     "type": "number",
     "minimum": 0
    },
    "dry_bulb": {
     "type": "number"
    },
    "enthalpy": {
     "type": "number"
    },
    "wet_bulb": {
     "type": "number"
    },
    "dew_point": {
     "type": "number"
    },
    "humidity_ratio": {
     "type": "number",
     "minimum": 0
    },
    "relative_humidity": {
     "type": "number",
     "maximum": 100,
     "minimum": 0
    }
   },
   "description": "Air entering the coil: exactly two of dry_bulb, wet_bulb, dew_point, relative_humidity (%), humidity_ratio (lb/lb or g/kg), enthalpy (BTU/lb or kJ/kg), grains (gr/lb), in `units`. With outdoor_air and return_air but no outdoor air amount, it is the mixed air and the outdoor air % is back-calculated.",
   "additionalProperties": false
  },
  "elevation": {
   "type": "number",
   "default": 0,
   "maximum": 30000,
   "minimum": -1500,
   "description": "Site elevation, ft (IP) or m (SI); sets the atmospheric pressure. Default 0 (sea level)."
  },
  "return_air": {
   "type": "object",
   "properties": {
    "grains": {
     "type": "number",
     "minimum": 0
    },
    "dry_bulb": {
     "type": "number"
    },
    "enthalpy": {
     "type": "number"
    },
   
… (truncated)
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "mode": "cooling",
  "loads": {
   "tons": 32.736,
   "total": 392.833,
   "latent": 122.833,
   "sensible": 270,
   "sensible_heat_ratio": 0.687,
   "total_from_enthalpy": 399.538
  },
  "notes": [],
  "steps": [
   {
    "step": "Atmospheric pressure",
    "reference": "ASHRAE Handbook—Fundamentals (2021), Ch. 1 Psychrometrics, Eq. 3",
    "calculation": "p = 14.696 × (1 − 6.8754×10⁻⁶ × Z)^5.2559 = 14.696 × (1 − 6.8754×10⁻⁶ × 0)^5.2559 = 14.6960 psia"
   },
   {
    "step": "Entering air state",
    "reference": "ASHRAE Handbook—Fundamentals (2021), Ch. 1 Psychrometrics",
    "calculation": "pws(67.00 °F wet bulb) = 0.32772 psia (ASHRAE Ch. 1 Eq. 6)"
   },
   {
    "step": "Entering air state",
    "reference": "ASHRAE Handbook—Fundamentals (2021), Ch. 1 Psychrometrics",
    "calculation": "Ws* = 0.621945 × pws / (p − pws) = 0.014185 lb/lb (saturated at the wet bulb)"
   }
  ],
  "units": "IP",
  "mixing": null,
  "airflow": 10000,
  "leaving": {
   "grains": 60.42,
   "density": 0.07667,
   "dry_bulb": 55,
   "enthalpy": 22.569,
   "wet_bulb": 54,
   "dew_point": 53.29,
   "humidity_ratio": 0.008631,
   "vapor_pressure": 0.20116,
   "specific_volume": 13.1549,
   "relative_humidity": 93.95
  },
  "entering": {
   "grains": 78.18,
   "density": 0.07301,
   "dry_bulb": 80,
   "enthalpy": 31.447,
   "wet_bulb": 67,
   "dew_point": 60.32,
   "humidity_ratio": 0.011169,
   "vapor_pressure": 0.25926,
   "specific_volume": 13.8494,
   "relative_humidity": 51.1
  },
  "pressure": 14.696,
  "elevation": 0,
  "condensate": 13.69,
  "next_calls": [
   {
    "why": "What duct size carries 10000 CFM at 0.08 in. w.g. / 100 ft?",
    "tool": "hvac_duct_size",
    "price": "$0.002",
    "arguments": {
     "units": "IP",
     "airflow": 10000,
     "friction_rate": 0.08
    }
   }
  ],
  "references": [
   "ASHRAE Handbook—Fundamentals (2021), Ch. 1 Psychrometrics",
   "Standard-air load equations: Qs = 1.08·CFM·ΔT, Ql = 4840·CFM·ΔW, Qt = 4.5·CFM·Δh"
  ],
  "solved_for": "loads",
  "unit_labels": {
   "area": "ft²",
   "load": "MBH (1,000 BTU/h)",
   "grains": "gr / lb dry air",
   "length": "in",
   "airflow": "CFM",
   "density": "lb / ft³",
   "enthalpy": "BTU / lb dry air",
   "pressure": "psia",
   "velocity": "FPM",
   "elevation": "ft",
   "condensate": "gal / h",
   "temperature": "°F",
   "friction_rate": "in. w.g. / 100 ft",
   "humidity_ratio": "lb water / lb dry air",
   "specific_volume": "ft³ / lb dry air",
   "relative_
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/hvac-coil-load-calculator-e4ba3784/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
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