The volute — the spiral housing around a centrifugal impeller — can be moulded from glass-filled polyamide or formed from steel. Both move air; they fail in different ways and cost differently. This comparison sets out the trade-offs so the housing is chosen by the application, not by habit.
Quick comparison
| Criterion | Plastic volute (PA66-GF) | Metal volute (galvanised / stainless) |
|---|---|---|
| Typical weight | 30–50% lighter than steel | Heavier; needs stronger mounting |
| Corrosion | No rust; unaffected by humidity and salt mist | Galvanised resists; untreated steel corrodes |
| Continuous air temperature | Typically +60 °C to +80 °C | 200 °C+ depending on grade |
| Fire behaviour | Thermoplastic; melts and can feed a fire | Non-combustible; contains fire |
| Impact / abuse resistance | Good, but can crack on hard impact | High; dents rather than cracks |
| Inlet and outlet geometry | Molded radii and bellmouth at no extra cost | Formed; tighter radii cost more |
| Tooling cost | Higher upfront (injection mould) | Low; sheet-metal dies are cheaper |
| Cost per unit at volume | Low — amortised tooling, no finishing | Higher material and labour content |
| Noise (structure-borne) | Lower mass, less drumming | Can resonate; needs damping |
| Repairability | Replace the part | Weld or panel repair possible |
Where plastic wins
Range hoods and air curtains. Grease-laden kitchen air is corrosive and the housing sits inside a consumer appliance where weight and cost matter. Moulded PA66-GF volutes resist detergents and humidity, and the molded bellmouth keeps noise down in a tight cabinet. The SF146A dual-inlet series is built this way for exactly this duty.
ERV / HRV cores. A ventilation core is a cold, damp, condensing environment. Steel needs coating; plastic does not. Light weight also matters because the unit hangs on a wall.
AHU and FCU modules. When the air is filtered and below 60 °C, a molded housing removes a whole finishing step and cuts shipping weight. The BC280 backward-curved series is typical of this use.
Salt-mist and coastal duty. Marine and coastal HVAC units see chloride-laden air. Glass-filled polyamide is unaffected; galvanised steel is not.
Where metal wins
Hot air. Kitchen canopy ducting, process exhaust and drying ovens run above the softening range of thermoplastics. Once continuous temperature passes roughly 80 °C, specify metal.
Fire containment. In grease-duct and commercial cooking applications, a thermoplastic housing can melt and add fuel to a duct fire. Metal is the code-friendly choice.
Abrasive or particulate-laden air. Dust and grit erode a plastic surface and can crack it on impact; steel wears predictably.
Very large impellers. Above roughly 400 mm, molding tools and wall thickness become impractical, and steel is the economical route.
How the two fail
Plastic failures are usually thermal or mechanical: creep near the temperature limit, cracking after impact, or thread stripping at mounting points. They are predictable and avoidable by staying inside the envelope.
Metal failures are usually corrosion or resonance: rust at untreated seams and fixings, or a housing that drums at a particular speed. Both are solvable with the right grade and damping.
Neither failure mode is cheaper than choosing the right housing at specification time.
Selection checklist
- Continuous air temperature — under 60 °C: plastic is normally safe; 60–80 °C: check the compound datasheet; above 80 °C: metal.
- Fire strategy — grease ducts and cooking canopies: metal.
- Corrosion environment — coastal, marine, condensing ERV: plastic; hot and dry industrial: either.
- Unit weight budget — wall-hung or ceiling-mounted appliances favour plastic.
- Volume — above a few thousand units per year, molded tooling pays back quickly.
- Impeller size — above ~400 mm, plan for metal.
What SUNXFAN® supplies
The range covers both construction routes: molded PA66-GF25 dual-inlet and backward-curved housings for appliance, ERV and AHU duty, and metal-housed units for hotter or heavier duty. Material grades and their test coverage are documented on the quality and testing page, including the REACH SVHC screening that applies to the shared raw-material grades.
If the duty point is near a boundary — 70 °C continuous, coastal air, grease exposure — send the operating envelope with the enquiry and the housing will be specified with the margin, not against it.