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Free Dehumidifier Sizing Tool

Dehumidifier Sizing Calculator

Get the Capacity Right

Use room size, temperature and humidity to calculate the correct dehumidifier output in litres per day. No guesswork, no undersized junk, no energy-wasting monsters.

Size My Dehumidifier

Damp Still Coming Back?

Dehumidifiers only manage moisture in the air. They do not fix leaking masonry, failed render, high ground levels, or condensation driven by cold surfaces.

If you’re emptying the tank every day and the problem never goes away, there’s usually a building defect behind it.

Book a Damp Survey

Enter Your Room Details

Measure longest wall
Measure shortest wall
Standard UK ceilings: 2.4–2.7m
Damp rooms often 70%+. Use a hygrometer if possible.
Ideal for UK homes: 50–60%
Most UK living rooms: 16–22°C
Select the level that best describes your situation
Industry Standard Sizing Guidelines:
  • Small (10-12L/day): Single rooms ≤20m², light condensation
  • Medium (12-20L/day): Large rooms 20-40m² or moderate damp
  • Large (20-30L/day): Whole flats, severe damp, or after leaks
  • Commercial (30L+): Whole houses, commercial spaces
  • Based on BDPA & Property Care Association standards

Find Your Perfect Dehumidifier

Enter your room details to calculate the ideal dehumidifier capacity

Understanding Dehumidifier Sizing

Learn why correct sizing matters and how capacity affects performance.

Capacity Calculation

Proper sizing considers: Room volume × Humidity level × Temperature × Air changes × Usage factors. Undersized units run constantly, oversized units waste energy.

Temperature Impact

Compressor dehumidifiers lose efficiency below 18°C. Desiccant models work better in cooler spaces (5-20°C). Always consider your room's average temperature.

Energy Efficiency

Correctly sized units use 30-50% less energy. Look for A++ energy ratings. A 20L/day unit running 8 hours often costs less than a 10L/day unit running 20 hours.

Dehumidifier Selection Guide

1. By Room Size & Type
  • Small bedrooms (≤15m²): 10-12L/day compressor
  • Living rooms (15-30m²): 12-20L/day compressor
  • Kitchens/bathrooms: Add 25% capacity for moisture sources
  • Open-plan spaces: Calculate total area, add 20%
  • Basements/garages: Desiccant type if <15°C
2. Essential Features
  • Humidistat: Automatic humidity control (essential)
  • Auto-defrost: For compressor models in cool rooms
  • Continuous drainage: For frequent use (hose included)
  • Timer: Programmable operation
  • Air filter: HEPA for allergy sufferers
  • Noise level: <45dB for bedrooms, <50dB for living areas
3. Usage Tips
  • Close windows/doors when running
  • Place centrally, not in corners
  • Empty tank daily or use continuous drainage
  • Clean filters monthly (affects efficiency)
  • Run during/after high moisture activities
  • Use timer for overnight running when humidity peaks
  • Target 50-60% RH for optimal comfort
4. When Professional Help Is Needed
  • Persistent damp despite dehumidifier use
  • Visible mould growth returning
  • Damp patches on walls/ceilings
  • Musty smells that won't go away
  • Suspected rising/penetrating damp
  • Structural damp issues
  • Condensation on multiple surfaces

Need Professional Damp Diagnosis?

Dehumidifiers treat symptoms, not causes. If you have persistent damp or mould, the underlying issue needs proper diagnosis. Our surveys identify whether you have rising damp, penetrating damp, condensation, or other issues.

Moisture Mapping

Identify exact damp patterns and sources

Thermal Imaging

Detect cold spots and thermal bridges

Specific Solutions

Tailored recommendations for your property

Our surveys determine whether a dehumidifier is the right solution or if other damp-proofing measures are needed.

Professional Damp Surveys

Identify & Solve Your
Damp Problems

Our experienced damp specialists provide comprehensive surveys to accurately diagnose moisture issues. Get a detailed report with actionable solutions tailored to your property.

40 Years Experience
Trusted expertise
Professional Surveyors
Expert assessment
Detailed Report
Clear recommendations

We Detect & Solve

Rising Damp
Ground moisture
Condensation
Excess humidity
Penetrating Damp
Leaks & seepage
Mould Growth
Health hazards