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Commonly Used Insulation Materials for Air Conditioning Ducts: Selecting the Right Material for Energy Savings and Reliability
2025-07-04
Commonly Used Insulation Materials for Air Conditioning Ducts
Selecting the Right Material for Energy Savings and Reliability
Air ducts in HVAC systems act as "blood vessels," transporting conditioned air. The quality of duct insulation directly impacts system efficiency, operational costs, and indoor environmental health and comfort. So it is important to choose a suitable material for HVAC insulation.
Appropriate materials can prevent pipe condensation and reduce additional heat loss.
Here are several common materials for pipe insulation. You can choose the one that suits you best according to your personal circumstances.
1. Fiberglass
- Key Characteristics:
- Made from molten glass fibers; yellow-brown/white cotton-like material.
- Density: 24–48 kg/m³ (ISO 29471).
- Open-cell structure; traps air.
- Non-combustible (Class A/A1 per GB 8624/EN 13501).
- Cost-effective.
- Thermal Performance:
- Thermal conductivity (λ): 0.031–0.044 W/(m·K) (ASTM C177, ISO 8301).
- Suitable for supply/return ducts in comfort HVAC.
- Advantages:
- Fire Resistance: Class A/A1.
- Acoustic Performance: Reduces vibration/airflow noise (NRC 0.6–1.0 per ASTM C423).
- Low Cost: Economical for large-scale projects.
- Lightweight & Flexible: Easy to install on bends/fittings.
- Disadvantages:
- Fiber Irritation: Requires PPE (gloves, mask, goggles) during installation. Post-installation, foil facing prevents fiber release.
- Moisture Sensitivity: Open-cell structure absorbs water, degrading insulation and promoting mold. Requires robust vapor barrier (e.g., foil laminate).
- Low Structural Strength: Prone to compression damage.
- Aesthetics: Requires additional cladding for visual appeal.
2. Rock Wool
- Key Characteristics:
- Made from molten basalt/slag; yellow-green/gray-brown.
- Density: 40–100 kg/m³ (ISO 29471).
- Open-cell structure; traps air.
- Non-combustible (Class A/A1).
- Superior temperature resistance (>600°C).
- Thermal Performance:
- λ: 0.033–0.046 W/(m·K) (ASTM C177).
- Comparable to fiberglass.
- Advantages:
- Fire Resistance: Best-in-class (Class A/A1), ideal for fire-rated ducts (e.g., smoke control systems).
- High-Temperature Stability: Maintains integrity to 700°C.
- Acoustic Performance: Effective noise absorption (NRC 0.7–1.0).
- Hydrophobicity (Premium Grades): Resists water penetration.
- Disadvantages:
- Fiber Irritation: Requires full PPE during handling.
- Moisture Absorption: Loses R-value when wet; requires vapor barrier.
- Weight: Heavier than fiberglass; structural support needed.
- Higher Cost: ~15–30% more expensive than fiberglass.
3. Rubber Foam
- Key Characteristics:
- Physically foamed EPDM rubber; black/dark gray flexible sheets/tubes.
- Closed-cell structure (cells >90% sealed per ASTM D1056).
- Highly elastic.
- Thermal Performance:
- λ: 0.032–0.038 W/(m·K) (ASTM C177) — best-in-class.
- Advantages:
- Water/Vapor Resistance: Blocks moisture ingress (WVT <0.10 perm per ASTM E96). Ideal for humid/outdoor applications (e.g., chilled water pipes, ducts).
- Flexibility: Conforms to irregular surfaces without gaps.
- Fiber-Free: Safe installation.
- Condensation Control: Prevents surface condensation.
- Durability: Resists UV, ozone, chemicals (ASTM G151/G155).
- Disadvantages:
- Fire Rating: Limited to Class B1 (GB 8624)/Euroclass C/E per EN 13501. Not suitable for fire-rated ducts.
- Cost: Highest among compared materials.
- Temperature Limit: Max continuous exposure: 125°C (ASTM C411).
- Compression: Vulnerable to permanent deformation under load.
4. Phenolic Foam Board
- Key Characteristics:
- Rigid board from resol resin + foaming agents; multicolored.
- Closed-cell structure (cells >85% sealed).
- Thermal Performance:
- λ: 0.020–0.030 W/(m·K) (ASTM C177) — highest efficiency.
- Advantages:
- Thermal Efficiency: Highest R-value per thickness.
- Fire Performance: Class A2 (EN 13501)/limited-combustible (ASTM E84).
- Structural Rigidity: Resists compression (strength >150 kPa per ISO 844).
- Low Smoke/Toxicity: Limited smoke density (ASTM E662).
- Disadvantages:
- Cost: Most expensive option.
- Installation Complexity: Requires precision cutting, sealing (joints ≥80% contact), and mechanical fastening.
- Brittleness: Prone to chipping/breakage.
- Alkali Sensitivity: Degrades in high-pH environments (e.g., concrete contact).
Material Selection Guide
| Key Property | Fiberglass | Rockwool | EPDM Foam | Phenolic Foam |
|---|---|---|---|---|
| λ [W/(m·K)] | 0.031–0.044 | 0.033–0.046 | 0.032–0.038 | 0.020–0.030 |
| Fire Rating | A/A1 (Best) | A/A1 (Best) | B1/C (Limited) | A2 (Limited) |
| Moisture Resistance | Poor | Moderate | Excellent | Excellent |
| Thermal Efficiency | Good | Good | Very High | Highest |
| Installation Ease | Good (Flexible) | Moderate (Heavy) | Best (Flexible) | Poor (Rigid) |
| Fiber-Free | ❌ | ❌ | ✔️ | ✔️ |
| Max Temp (°C) | 250–400 | >600 | 110–125 | 150 |
| Cost | Lowest | Moderate | High | Highest |
| Ideal Applications | Indoor ducts (dry) | Fire-rated ducts | Humid/outdoor systems | High-efficiency ducts |
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