After mould remediation, a dehumidifier is often the most cost-effective ongoing prevention tool, but buying the wrong one means wasted electricity, inadequate performance and mould recurrence. Size it correctly for your space, choose features appropriate for Illawarra’s climate, and place it where it does the most work.
This guide gives you the information to make the right purchase for your specific situation in Wollongong, Shellharbour, Kiama or anywhere across the Illawarra.
Why Post-Remediation Humidity Control Matters
Mould requires relative humidity above 65-70% (sustained over time) to grow. Wollongong’s coastal climate sits at 65-75% average relative humidity year-round, consistently in the risk zone. A home without any active humidity control is relying on passive ventilation alone to keep indoor humidity below the mould threshold. In older, poorly ventilated homes, this isn’t sufficient.
After professional mould remediation, the mould has been removed and surfaces treated. The moisture conditions that caused the mould, if structural issues are addressed, are reduced but not necessarily eliminated. A dehumidifier provides the insurance layer that keeps humidity below the mould growth threshold even when ventilation is limited (winter with closed windows, periods of high occupancy).
Sizing: The Most Important Decision
Dehumidifier capacity is measured in litres per day (L/day), the volume of water removed from the air in a 24-hour period at standard test conditions. Under-sizing is the most common mistake: a 10 L/day unit in a damp 4-bedroom Wollongong home runs constantly and never gets humidity below 70%.
Basic sizing guide:
| Space Condition | Up to 50 m² | 50-100 m² | 100-150 m² | 150-250 m² |
|---|---|---|---|---|
| Slightly damp (55-65% RH) | 10 L/day | 14 L/day | 20 L/day | 25 L/day |
| Moderately damp (65-75% RH) | 14 L/day | 20 L/day | 25 L/day | 35 L/day |
| Very damp (75%+ RH) | 20 L/day | 25 L/day | 35 L/day | 50 L/day |
| Post-water damage drying | 25-50 L/day | 40-70 L/day | 50-90 L/day | Multiple units |
For most post-remediation residential applications in Illawarra’s moderately-to-very-damp climate:
- 2-3 bedroom unit: 20-25 L/day
- 3-4 bedroom house: 25-35 L/day
- 4+ bedroom house with subfloor issues: 35-50 L/day
Important: Manufacturer capacity ratings are at 30°C / 80% RH test conditions. In cooler winter conditions (15-20°C), actual removal capacity can drop to 40-60% of the rated capacity. For winter use in Illawarra homes, upsize accordingly.
Key Features to Look For
Humidistat with Setpoint Control
A humidistat lets you set a target humidity (we recommend 55-60% for mould prevention) and the unit runs only until that level is reached, then cycles off. Without a humidistat, the unit runs continuously, consuming more electricity and potentially over-drying the air.
This is a must-have feature, do not buy a unit without it.
Continuous Drain Option
Units with a continuous drain option allow you to connect a small hose that gravity-drains water from the unit’s reservoir into a floor drain, washing machine outlet or outside. This eliminates the need to empty the tank manually, essential for any unattended operation or large-capacity units that fill quickly.
A continuous drain feature is particularly important in very damp post-remediation scenarios where the unit may collect 10-30 litres per day in the first week.
Auto-Restart After Power Outage
This feature restores the unit to its last settings after a power outage rather than requiring manual restart. Important for units running unattended (in an investment property, during a vacancy period).
Refrigerant vs Desiccant Technology
Refrigerant (compressor) dehumidifiers work similarly to an air conditioner, passing air over a cold coil to condense moisture. They are most efficient at temperatures above 20°C but lose significant efficiency below 15°C. Most effective for summer use or in heated indoor spaces.
Desiccant dehumidifiers pass air over a chemical desiccant wheel that absorbs moisture. They work effectively at temperatures as low as 1°C, making them far superior for winter use in Illawarra homes where interior temperatures in winter can drop below 15°C in unheated bedrooms. They also tend to be quieter. Downside: slightly higher electricity consumption at warm temperatures.
For year-round use in Illawarra, a desiccant dehumidifier or a high-quality refrigerant unit rated for low-temperature operation is recommended. Don’t buy a budget refrigerant dehumidifier and expect it to perform in winter.
Wi-Fi and App Control
Increasingly common in higher-end units. Useful for investment property or holiday rental managers who want to monitor humidity remotely and confirm the unit is operating between visits.
Recommended Placement
Post-remediation placement, place in the room that had the worst mould, or in the central living area if mould was widespread. Run with internal doors open where possible to circulate dry air throughout the home.
Bedroom use, if the mould was primarily in bedrooms, a smaller unit (10-14 L/day) in the bedroom with the door closed at night is appropriate. Look for a quiet model (noise level below 45 dB) for bedroom use.
Subfloor placement, standard refrigerant dehumidifiers are not appropriate for subfloor voids (too cold, too humid, poor access for maintenance). Subfloor ventilation systems with dedicated fans are the appropriate solution for subfloor moisture. See our guide on subfloor ventilation.
Do not place dehumidifiers directly against walls (block airflow), in corners (same issue), directly under air conditioning vents (makes the unit work against cooling), or in enclosed cupboards.
Budget Guidance
| Tier | L/Day | Price Range AUD | Best For |
|---|---|---|---|
| Entry level | 10-16 | $200 to $400 | Small apartment, secondary room |
| Mid-range | 20-25 | $400 to $700 | 3 bedroom home, primary use |
| Premium | 25-35 | $700 to $1,200 | 4 bedroom home, year-round use |
| Commercial/high capacity | 35-70+ | $1,200 to $3,000+ | Severe damp, investment property |
For most Illawarra post-remediation residential applications, a $500-$800 mid-range to premium unit with humidistat, continuous drain and low-temperature capability is the right investment. The cost difference between a $300 unit and a $700 unit is recovered in electricity savings within 1-2 years of correct operation.
Operating Costs
A 25 L/day unit typically uses 350-500W at full operation. At an electricity rate of $0.30/kWh, this costs approximately:
- Continuous operation: $2.50-$3.60 per day
- Cycling operation (humidistat-controlled at 55%): $0.60-$1.50 per day in normal conditions
Running costs are meaningful, this is another reason to buy a unit with humidistat control rather than one that runs continuously.
Maintenance
Clean the air filter every 2-4 weeks (more frequently in dusty environments). A blocked filter reduces airflow and capacity significantly. Wipe the reservoir with dilute white vinegar if any mould or mineral deposits appear. Annual coil cleaning (refrigerant units) from a service technician maintains efficiency.
Frequently Asked Questions
How long should I run a dehumidifier after mould remediation? Run continuously (on humidistat setpoint) for the first 2 weeks after remediation to stabilise indoor humidity and dry out any residual moisture in building materials. After this, continue to run whenever indoor humidity exceeds 60%, which in Illawarra’s climate typically means daily use in winter and as needed in summer.
Will a dehumidifier stop mould from coming back? A correctly sized dehumidifier maintaining indoor RH below 60% prevents new mould growth on treated surfaces, provided the structural moisture source is also addressed. It will not prevent regrowth if active water ingress (leaking roof, rising damp) continues.
Can I use a dehumidifier in a bathroom? Standard residential dehumidifiers are not rated for bathroom use (water ingress risk). For bathroom humidity control, an appropriate-spec exhaust fan is the right tool. A dehumidifier in the hallway adjacent to the bathroom, with the door left open after showering, can assist if exhaust ventilation is inadequate.
Are cheap supermarket dehumidifiers worth buying? Entry-level units ($150-$250) can work for small, mildly damp spaces. For seriously mould-affected homes in Illawarra’s climate, they typically can’t maintain adequate humidity control, they fill their tank quickly, require constant manual emptying to keep running, and may not have adequate humidistat accuracy.
My dehumidifier collects a lot of water, does this mean the mould is coming back? High water collection is normal in the first 2-4 weeks post-remediation as the building materials release stored moisture. If high collection continues indefinitely beyond this initial period, it suggests either ongoing moisture entry or an unresolved high-humidity source (poor ventilation, subfloor issues) that needs investigation.
Need advice on the right dehumidifier for your Illawarra home after mould remediation, or to confirm your remediation is properly complete? Contact Illawarra Mould Removal.