{
    "name": "Greenhouse Ventilation Calculator",
    "url": "https://calculators.geekmidst.com/calculators/greenhouse-ventilation-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/greenhouse-ventilation-calculator.md",
    "category": "Agriculture",
    "description": "Size greenhouse exhaust fans from the house volume and the air changes per hour you want, in m³/h and CFM, and count how many fans you need.",
    "summary": "Required airflow is the greenhouse volume times the air changes per hour. Divide it by one fan’s rated capacity to count fans.",
    "also_called": [
        "Greenhouse fan calculator",
        "Greenhouse CFM calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "units",
            "label": "Units",
            "type": "segmented",
            "default": "metric",
            "options": {
                "metric": "Metres (m³/h)",
                "imperial": "Feet (CFM)"
            }
        },
        {
            "name": "length",
            "label": "Length",
            "type": "number",
            "default": "30"
        },
        {
            "name": "width",
            "label": "Width",
            "type": "number",
            "default": "9"
        },
        {
            "name": "eave_height",
            "label": "Side-wall (eave) height",
            "type": "number",
            "default": "3"
        },
        {
            "name": "ridge_height",
            "label": "Ridge height",
            "type": "number",
            "default": "5"
        },
        {
            "name": "ach",
            "label": "Air changes per hour",
            "type": "number",
            "default": "60"
        },
        {
            "name": "fan_capacity",
            "label": "Capacity of one fan (optional)",
            "type": "number",
            "default": "15000",
            "optional": true
        }
    ],
    "outputs": [
        {
            "key": "airflow_m3h",
            "label": "Required airflow",
            "format": "number"
        },
        {
            "key": "airflow_cfm",
            "label": "Required airflow",
            "format": "number"
        },
        {
            "key": "airflow_m3s",
            "label": "Required airflow",
            "format": "number"
        },
        {
            "key": "volume_m3",
            "label": "Greenhouse volume",
            "format": "number"
        },
        {
            "key": "volume_ft3",
            "label": "Greenhouse volume",
            "format": "number"
        },
        {
            "key": "fans",
            "label": "Fans needed",
            "format": "integer"
        }
    ],
    "formula": {
        "text": "Volume = Length × Width × (Eave height + (Ridge − Eave) ÷ 2);  Airflow = Volume × Air changes per hour;  Fans = Airflow ÷ Fan capacity, rounded up",
        "variables": {
            "Air changes per hour": "how many times the house air is replaced each hour",
            "1 m³": "35.3147 ft³"
        }
    },
    "worked_example": {
        "inputs": {
            "units": "metric",
            "length": "30",
            "width": "9",
            "eave_height": "3",
            "ridge_height": "5",
            "ach": "60",
            "fan_capacity": "15000"
        },
        "steps": [
            "Volume = 30 × 9 × (3 + 2 ÷ 2) = 1080 m³.",
            "Airflow = 1080 × 60 = 64,800 m³/h (38,140 CFM).",
            "Fans = 64,800 ÷ 15,000 = 4.32, so 5 fans."
        ],
        "result": "A 30 × 9 m gable greenhouse needs 64,800 m³/h for one air change per minute: five 15,000 m³/h fans."
    },
    "interpretation": "Fan ratings fall as static pressure rises, so use the capacity at the pressure your installation will run at (often 0.1 inch of water or about 25 Pa).",
    "assumptions": [
        "A simple gable roof; for a flat roof enter the same eave and ridge height."
    ],
    "limitations": [
        "The air change rate is your input; the calculator does not model solar heat gain or evaporative cooling."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "How do I size for a hoop house?",
            "answer": "Use the average height (roughly two-thirds of the peak for a semicircular hoop) as both eave and ridge height."
        },
        {
            "question": "Why use the volume and not the floor area?",
            "answer": "Air changes are defined on volume. Some guides use airflow per floor area instead; both lead to similar fan sizes for typical heights."
        }
    ],
    "sources": [],
    "related": [
        {
            "name": "Greenhouse Heating Load Calculator",
            "url": "https://calculators.geekmidst.com/calculators/greenhouse-heating-load-calculator"
        },
        {
            "name": "Compost Volume Calculator",
            "url": "https://calculators.geekmidst.com/calculators/compost-volume-calculator"
        }
    ],
    "disclaimer": null,
    "publisher": "GM¹X CalcVerse"
}