Dehumidifier Capacity Calculator

ANA›Life Services Authority›National Calculator Authority›Dehumidifier Capacity Calculator

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Dehumidifier Capacity Calculator

Estimate the dehumidifier capacity (pints per day) needed for your space based on room size, current humidity, and environmental conditions.

Room Area (sq ft)

Ceiling Height (ft)

Current Relative Humidity (%)

Room Temperature (°F)

Room Condition

Moderately damp (feels damp, musty odor sometimes) Very damp (always feels damp, musty odor) Wet (walls/floor sweat, seepage present) Extremely wet (standing water, flooding)

Number of Windows / Doors

Number of Occupants

Laundry Done in Room?

No Yes

Calculate

function dehCalc() { const resultDiv = document.getElementById('deh-result');

const area = parseFloat(document.getElementById('deh-area').value); const height = parseFloat(document.getElementById('deh-height').value); const humidity = parseFloat(document.getElementById('deh-humidity').value); const tempF = parseFloat(document.getElementById('deh-temp').value); const condition = parseInt(document.getElementById('deh-condition').value); const windows = parseFloat(document.getElementById('deh-windows').value); const occupants = parseFloat(document.getElementById('deh-occupants').value); const laundry = parseInt(document.getElementById('deh-laundry').value);

// --- Validation --- if (isNaN(area) || area Please enter a valid room area (sq ft).'; return; } if (isNaN(height) || height 20) { resultDiv.innerHTML = 'Ceiling height must be between 4 and 20 ft.'; return; } if (isNaN(humidity) || humidity 100) { resultDiv.innerHTML = 'Relative humidity must be between 50% and 100%.'; return; } if (isNaN(tempF) || tempF 120) { resultDiv.innerHTML = 'Temperature must be between 32°F and 120°F.'; return; } if (isNaN(windows) || windows Number of windows/doors cannot be negative.'; return; } if (isNaN(occupants) || occupants Number of occupants cannot be negative.'; return; }

// --------------------------------------------------------------- // FORMULA (based on AHAM / Energy Star dehumidifier sizing guide) // --------------------------------------------------------------- // Step 1: Volume of space (cubic feet) const volume = area * height;

// Step 2: Base capacity from AHAM table (pints/day) based on area & condition // AHAM baseline: moderately damp room at ~500 sq ft = 10 pints/day // Scale linearly with area; condition adds incremental pints per 500 sq ft const conditionAddPerUnit = [0, 4, 8, 12]; // extra pints per 500 sq ft block const areaUnits = area / 500; let basePints = 10 * areaUnits + conditionAddPerUnit[condition] * areaUnits;

// Step 3: Temperature correction factor // Warmer air holds more moisture; dehumidifier works harder in heat // Factor derived from psychrometric approximation: // At 70°F → factor 1.0; each 10°F above adds ~5%; below subtracts ~5% const tempFactor = 1 + (tempF - 70) * 0.005;

// Step 4: Humidity correction factor // At 60% RH → factor 1.0; each 10% above adds ~10% const humidityFactor = 1 + (humidity - 60) * 0.01;

// Step 5: Moisture load additions (pints/day) // Each window/door adds ~0.5 pints/day (infiltration) const windowLoad = windows * 0.5; // Each occupant adds ~0.5 pints/day (respiration & perspiration) const occupantLoad = occupants * 0.5; // Laundry adds ~4 pints/day const laundryLoad = laundry * 4;

// Step 6: Total capacity needed (pints/day) let totalPints = (basePints * tempFactor * humidityFactor) + windowLoad + occupantLoad + laundryLoad;

// Minimum floor: 10 pints/day for any occupied space totalPints = Math.max(totalPints, 10);

// Round up to nearest whole pint totalPints = Math.ceil(totalPints);

// Step 7: Convert to liters/day (1 pint = 0.473176 liters) const totalLiters = (totalPints * 0.473176).toFixed(1);

// Step 8: Recommended unit size (common commercial sizes) let recommendedSize = ''; if (totalPints Room Volume${volume.toLocaleString()} cu ft Room Condition${condLabels[condition]} Base Moisture Load (area + condition + temp + humidity)${baseDisplay} pints/day Window / Door Infiltration Load${windowLoad.toFixed(1)} pints/day Occupant Moisture Load${occupantLoad.toFixed(1)} pints/day Laundry Moisture Load${laundryLoad.toFixed(1)} pints/day

Required Dehumidifier Capacity ${totalPints} pints/day (${totalLiters} L/day)

Recommended Unit Size${recommendedSize} Target Relative Humidity${targetRH}% RH

⚡ Tip: Choose a unit rated at least 10–15% above the calculated capacity to account for efficiency losses and ensure the unit doesn't run continuously.

`; }

#### Formula

1. Volume: V = Area (sq ft) × Ceiling Height (ft) 2. Base Capacity (pints/day):   Base = [10 + ConditionFactor] × (Area ÷ 500)   ConditionFactor: Moderately damp = 0, Very damp = 4, Wet = 8, Extremely wet = 12 (per 500 sq ft) 3. Temperature Factor:   Tfactor = 1 + (T°F − 70) × 0.005   (Each 10°F above 70°F increases load ~5%) 4. Humidity Factor:   RHfactor = 1 + (RH% − 60) × 0.01   (Each 10% above 60% RH increases load ~10%) 5. Additional Loads:   Windows/Doors: 0.5 pints/day each   Occupants: 0.5 pints/day each   Laundry: 4.0 pints/day 6. Total Capacity:   Total = (Base × Tfactor × RHfactor) + Window Load + Occupant Load + Laundry Load   Minimum: 10 pints/day 7. Unit Conversion: 1 pint = 0.4732 liters

#### Assumptions & References

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