If you've recently encapsulated your crawl space—or you're planning to—you might be wondering whether you still need a dehumidifier. After all, you've just invested thousands of dollars to seal out moisture with a vapor barrier, closed vents, and insulation. Shouldn't that be enough?
The short answer is: Yes, an encapsulated crawl space absolutely needs a dehumidifier. In fact, installing a dehumidifier isn't just recommended—it's essential for the encapsulation system to work properly. Without a dehumidifier, your expensive encapsulation investment won't deliver the moisture control, air quality improvements, and structural protection you're counting on.
This article explains why dehumidifiers are critical even in fully encapsulated crawl spaces, how to choose the right model, and what happens when homeowners skip this crucial component.
Understanding Crawl Space Encapsulation
Before diving into why dehumidifiers are necessary, let's clarify what crawl space encapsulation actually accomplishes.
What Is Crawl Space Encapsulation?
Crawl space encapsulation is a comprehensive moisture control strategy that transforms your crawl space from a vented, damp area into a sealed, controlled environment. The process involves sealing the crawl space off from external moisture sources and outdoor air.
Key encapsulation steps include:
- Installing a heavy-duty vapor barrier (typically 10-20 mil polyethylene) over the floor and walls
- Sealing all crawl space vents to prevent humid outdoor air from entering
- Insulating crawl space walls to create a conditioned space
- Sealing gaps, cracks, and penetrations around pipes, wiring, and access doors
- Installing a dehumidifier to manage moisture within the sealed environment
How Encapsulation Works
Encapsulation works by creating a barrier between your crawl space and external moisture sources. The vapor barrier prevents ground moisture from evaporating into the crawl space air. Sealed vents stop humid outdoor air from entering during summer months.
By creating this closed system, encapsulation dramatically reduces the amount of moisture entering your crawl space. Instead of fighting constant moisture intrusion from below and outside, you're working with a much smaller, more manageable moisture load.
Key Components of an Encapsulated Crawl Space
A complete encapsulation system includes several integrated components:
Vapor Barrier:
- Heavy-duty polyethylene sheeting (10-20 mil thickness)
- Covers floor completely and extends 12-18 inches up walls
- All seams sealed with tape or caulk
- Secured to walls and floor with fasteners
Vent Sealing:
- All foundation vents closed and sealed
- Prevents outdoor air infiltration
- Maintains controlled interior environment
Insulation:
- Spray foam or rigid foam on walls
- Creates conditioned space within home envelope
- Improves energy efficiency
Drainage:
- Sump pump if needed for water management
- Interior drainage system for severe moisture
Dehumidification:
- This is where many homeowners make a critical mistake by thinking it's optional
Why Encapsulation Alone Isn't Enough
Here's the part that surprises most homeowners: encapsulation significantly reduces moisture intrusion, but it doesn't eliminate moisture entirely.
Encapsulation Reduces—But Doesn't Eliminate—Moisture
Think of encapsulation as sealing the doors and windows of a greenhouse. You've stopped most outside air and moisture from entering, but the environment inside still needs management. Encapsulation dramatically reduces your moisture load—often by 80-90%—but that remaining 10-20% still creates problems if left unmanaged.
Encapsulation accomplishes:
- Blocks ground moisture vapor from entering through dirt floor
- Prevents humid outdoor air infiltration through vents
- Reduces air exchange between crawl space and outside
- Creates barrier against bulk water intrusion
Encapsulation does NOT accomplish:
- Remove existing moisture from the air
- Eliminate humidity from concrete foundation walls
- Prevent condensation on cooler surfaces
- Control moisture from internal sources
The Stack Effect and Indoor Humidity
Remember that up to 50% of the air in your home's first floor originates from your crawl space due to the stack effect. If your sealed crawl space maintains 70% humidity without a dehumidifier, that moisture-laden air is continuously drawn into your living spaces.
The result? High indoor humidity, musty odors, increased HVAC load, and the very problems encapsulation was meant to solve.
The Short Answer: Yes, You Need a Dehumidifier
Let's be absolutely clear: a dehumidifier is not optional for an encapsulated crawl space. It's a required component of a properly functioning encapsulation system.
Why Dehumidifiers Are Essential for Encapsulated Crawl Spaces
Industry experts, building scientists, and encapsulation professionals universally agree: encapsulation without dehumidification is an incomplete system. Here's why:
Encapsulation Creates Ideal Conditions for Dehumidifier Efficiency
In an encapsulated space, your dehumidifier works in an optimized environment. There's no constant moisture intrusion to fight against. The sealed system allows the dehumidifier to maintain target humidity levels efficiently with minimal energy consumption.
Think of it this way: running a dehumidifier in an open, vented crawl space is like air conditioning your home with windows open. Running a dehumidifier in an encapsulated crawl space is like air conditioning a sealed, insulated home—far more effective and efficient.
Encapsulation Concentrates Remaining Moisture
By sealing the space, you've eliminated most moisture sources but concentrated what remains. Without active moisture removal via dehumidification, that trapped humidity has nowhere to go. It accumulates, condenses on surfaces, and creates the perfect environment for mold—inside your sealed, expensive encapsulation system.
Building Science Requires Active Moisture Management
Modern building science recognizes that creating sealed spaces without mechanical moisture control leads to problems. This is why basement finishing requires dehumidification, why bathrooms need exhaust fans, and why encapsulated crawl spaces need dehumidifiers.
Passive moisture control (vapor barriers, sealing) must be paired with active moisture control (dehumidification) for reliable, long-term performance.
Benefits of Adding a Dehumidifier to Your Encapsulated Crawl Space
The combination of encapsulation plus dehumidification delivers benefits neither system can achieve alone.
Complete Moisture Control
Encapsulation reduces moisture load by 80-90%. The dehumidifier handles the remaining 10-20% plus any residual humidity. Together, they maintain ideal conditions (40-50% RH) reliably and efficiently.
This two-pronged approach addresses both:
- Source control (encapsulation blocks moisture entry)
- Moisture removal (dehumidification eliminates what remains)
Mold and Mildew Prevention
Maintaining humidity below 60% prevents mold growth entirely. The encapsulated environment gives your dehumidifier the advantage—it can easily maintain 45-55% RH in a sealed space, creating conditions where mold simply cannot establish.
Without the constant moisture intrusion of an open crawl space, the dehumidifier cycles on and off rather than running continuously, saving energy while preventing mold.
Improved Indoor Air Quality
The combination delivers superior indoor air quality benefits:
Encapsulation stops:
- Outdoor pollutants and allergens from entering
- Soil gases (including radon) from infiltrating
- Pest entry points
Dehumidification stops:
- Mold spore proliferation
- Musty odors from moisture
- Dust mite populations (which require high humidity)
Together, they ensure the air rising from your crawl space into living areas is clean, dry, and healthy.
Energy Efficiency Gains
Here's where the magic happens: encapsulation plus dehumidification is more energy-efficient than either system alone.
In open crawl spaces:
- Dehumidifiers run constantly fighting moisture intrusion
- Energy consumption: $50-80/month
- Never achieve optimal humidity levels
In encapsulated spaces with dehumidifiers:
- Dehumidifiers cycle on/off maintaining set points
- Energy consumption: $20-35/month
- Consistently maintain 45-55% RH
- Energy savings: $360-540 annually vs. open crawl space
Plus, reducing humidity load on your whole-home HVAC system saves additional energy—humid air is harder and more expensive to heat and cool.
How Dehumidifiers Work in Encapsulated Crawl Spaces
Understanding the synergy between encapsulation and dehumidification helps appreciate why both are necessary.
The Sealed Environment Advantage
In an encapsulated crawl space, your dehumidifier operates in an ideal environment:
No constant moisture intrusion means the unit isn't fighting a losing battle. It removes existing moisture, then cycles on only when needed to maintain set points.
Smaller moisture load allows proper sizing. In open crawl spaces, you often need oversized units running continuously. In encapsulated spaces, appropriately sized units handle the load efficiently.
Stable temperatures from insulation mean consistent dehumidifier performance. Units don't struggle with temperature extremes that affect efficiency.
Lower air exchange means the dry air you create stays in the space rather than being constantly replaced with humid outdoor air.
Choosing the Right Dehumidifier for Your Encapsulated Crawl Space
Proper equipment selection ensures optimal performance and efficiency.
Sizing Requirements for Encapsulated Spaces
Important: Encapsulated crawl spaces require less dehumidifier capacity than open spaces of the same size because moisture load is dramatically reduced.
General sizing for encapsulated crawl spaces:
|
Crawl Space Size |
Recommended Capacity |
Example AlorAir Model |
|
Up to 1,000 sq ft |
60-70 PPD |
Sentinel HD35P (70 PPD) |
|
1,000-1,500 sq ft |
90-120 PPD |
Sentinel HD55P (120 PPD) |
|
1,500-2,000 sq ft |
120-145 PPD |
Galaxy 60P (145 PPD) |
|
2,000-2,500 sq ft |
145-180 PPD |
Galaxy 85P (180 PPD) |
|
2,500+ sq ft |
180-200 PPD |
Sentinel HDi90 (198 PPD) |
Energy Efficiency Considerations
In encapsulated crawl spaces, energy efficiency delivers bigger savings because:
Lower runtime means efficiency gains compound over thousands of operating hours annually.
Stable conditions allow dehumidifiers to operate at peak efficiency rather than struggling against constant moisture intrusion.
ENERGY STAR models in encapsulated spaces typically cost $20-35/month to operate versus $50-80/month for same-capacity units in open crawl spaces.
Annual savings: $360-540 from reduced dehumidifier operation plus $200-400 from reduced HVAC load = $560-940 total annual energy savings from the encapsulation + dehumidifier combination.
Recommended AlorAir Models
For most encapsulated crawl spaces:
AlorAir Sentinel HD55P (120 PPD)
- Ideal for 1,200-1,500 sq ft encapsulated spaces
- Built-in pump, auto-defrost, Energy Star certified
- 2.3 L/kWh efficiency, 5-year warranty
- WiFi option available
- Shop Sentinel HD55P
AlorAir Galaxy 60P (145 PPD)
- Perfect for 1,500-2,000 sq ft encapsulated spaces
- Superior 2.4 L/kWh efficiency
- Integrated pump, rugged metal construction
- Shop Galaxy 60P
Installation Best Practices
Proper installation maximizes performance in your encapsulated crawl space.
Where to Position Your Dehumidifier
Optimal placement in encapsulated spaces:
- Central location when possible for even air distribution
- On top of vapor barrier in a slightly elevated area (avoid low spots where water might pool)
- Near power outlet (never use extension cords)
- Minimum 12 inches from walls for adequate airflow
- Accessible area for filter maintenance despite limited encapsulation access points
Drainage Setup Options
Gravity drainage to sump pump or exterior:
- Ideal if drain point is lower than dehumidifier
- Requires 1/4 inch per foot downward slope
- Simple, reliable, no moving parts
Pumped drainage (recommended):
- AlorAir pumps lift water up to 19.6 feet vertically
- Can drain to sump pump above unit level
- Can route to exterior discharge even through foundation walls
- Maximum flexibility
Electrical Requirements
- Dedicated, grounded outlet (never use extension cords)
- GFCI protection recommended for safety
- Easy access to circuit breaker if unit needs servicing
- Consider adding outlet during encapsulation if none exists in convenient location
Integration with Encapsulation System
Seal around power cord entry point in vapor barrier to maintain encapsulation integrity.
Route drain line under or through vapor barrier without creating leak points—seal all penetrations.
Coordinate with encapsulation contractor to identify optimal dehumidifier placement during encapsulation work.
Conclusion
The answer to "Does an encapsulated crawl space need a dehumidifier?" is an unequivocal yes. Encapsulation and dehumidification aren't competing solutions—they're complementary systems that work together to deliver complete moisture control.
Encapsulation provides:
- Barrier against ground moisture
- Sealed environment preventing outdoor air intrusion
- Energy efficiency improvements
- Pest exclusion
Dehumidification provides:
- Active moisture removal from sealed space
- Precise humidity control (40-50% RH)
- Mold prevention
- Optimal conditions for structural protection
Together, they deliver:
- Complete moisture control impossible with either alone
- Maximum energy efficiency and cost savings
- Superior indoor air quality
- Long-term structural protection
- Industry-compliant crawl space moisture management
Don't make the costly mistake of encapsulating without dehumidification. Budget for both systems from the start, and choose quality equipment designed specifically for crawl space applications.
Ready to complete your encapsulated crawl space system? Browse AlorAir's complete line of Energy Star crawl space dehumidifiers designed specifically for sealed crawl space environments. With models ranging from 70-235 PPD, built-in pumps, WiFi monitoring, and 5-year warranties, AlorAir delivers the reliable performance your encapsulated crawl space deserves.
Your encapsulation investment is only complete when paired with proper dehumidification. Protect your home, your air quality, and your investment with the right equipment from day one.
Frequently Asked Questions
Is a dehumidifier really necessary if I've already encapsulated my crawl space?
Yes, absolutely. Encapsulation dramatically reduces moisture intrusion but doesn't eliminate all moisture sources or remove existing humidity from the sealed space. Even perfectly encapsulated crawl spaces experience moisture migration through concrete, minor air infiltration, and internal sources like plumbing condensation.
Will my encapsulation fail without a dehumidifier?
Over time, yes. While the vapor barrier physically remains in place, the encapsulation system won't deliver its intended benefits without dehumidification. High humidity trapped in the sealed space leads to mold growth on the vapor barrier itself, condensation that can cause tape and sealant failure, musty odors that permeate living spaces via the stack effect, and continued wood rot despite the vapor barrier.
How much does it cost to run a dehumidifier in an encapsulated crawl space?
Dehumidifiers in encapsulated crawl spaces are remarkably efficient, typically costing $20-35 per month for Energy Star certified models. This is 60-75% less than running a dehumidifier in an open, vented crawl space ($50-80/month) because the sealed environment requires much less frequent operation.
What size dehumidifier do I need for an encapsulated crawl space?
Encapsulated crawl spaces require 30-40% less dehumidifier capacity than open spaces of the same size due to dramatically reduced moisture loads. For a 1,000 sq ft encapsulated space, a 60-70 PPD unit like the AlorAir Sentinel HD35P is sufficient. For 1,200-1,500 sq ft, choose 90-120 PPD (Sentinel HD55P).
Can I use a regular basement dehumidifier in my encapsulated crawl space?
No, you need a crawl space-specific dehumidifier even in encapsulated spaces. Standard basement units have vertical designs that don't fit in low-clearance crawl spaces (often <24 inches high), lack auto-defrost for low-temperature operation (crawl spaces still reach 40-50°F), feature plastic housing that degrades in harsh conditions, and don't include built-in pumps for drainage flexibility.
When should I run my crawl space dehumidifier—year-round or seasonally?
In encapsulated crawl spaces, run your dehumidifier year-round but expect seasonal variations in runtime. During humid months (typically May-September), the unit will cycle more frequently to maintain 45-50% RH. In dry winter months, it may run minimally or not at all if humidity naturally stays below target levels.
Do I still need to monitor humidity after installing a dehumidifier in my encapsulated crawl space?
Yes, regular monitoring ensures your system is working properly. Check humidity levels monthly using your dehumidifier's display or WiFi monitoring app (available on AlorAir WiFi models). Verify the space maintains 45-55% RH and the dehumidifier is cycling (not running 24/7).
