Do you build upblast or downblast roof ventilators, and how do I choose?
Both, and the choice is driven by re-entrainment. Upblast throws the exhaust up and away from the roof and from fresh-air intakes, so it is the default for fume, grease and process extract where you must not draw the discharge back into the building. Downblast discharges along the roof and suits clean building air where there is no contaminant to keep clear of intakes and a low plume is preferred. We also build wall-mounted centrifugal ventilators where roof access or structure rules out a roof unit. Tell us the extract type and where your intakes and the property boundary sit, and we set the configuration to that, not a default.
How do you keep weather and birds out of a roof fan?
A PRV is a weather-exposed machine first. We fit a spun or fabricated weather hood with an overlapping drip edge, a drain trough that sheds water clear of the motor, and a bird and vermin screen across the discharge. The motor is IP55 as standard, out of the airstream, with IP66 available on coastal or wash-down duty. A gravity or motorised backdraught damper closes the ventilator when the fan is off, so warm building air does not escape and reverse flow does not draw weather back in. The whole weatherproofing scope is shown on the GA drawing you approve.
The fan sits directly over offices. How quiet can you make it?
Roof and wall fans usually sit above occupied space, so both the fan noise and the discharge plume matter. We select backward-curved or airfoil wheels that run quiet and size the duty well left of the peak-noise zone, then design to below 80 dB(A) at 3 m as standard. Where the limit is tighter — an office, a hospital, or a boundary condition — we add discharge and inlet silencers and an acoustic-lined curb and engineer to the stated number. Tell us the sound limit and the measurement position and we predict and build to it before dispatch.
My extract carries solvent fume and grease. Is that a spark or fire risk on the roof?
It can be, and it is worth taking seriously because the fan sits above the building. A roof fan pulling solvent fume off a coating line or grease off a commercial kitchen is not moving clean air. For that duty we build spark-resistant construction to AMCA 99 — Type A, B or C selected to the ignition risk — with bonded earthing throughout, and for kitchen duty a cleanable construction with a grease drain. Where the area is classified for flammable vapour or combustible dust we self-declare ATEX Zone 2/22 per 2014/34/EU, Category 3. On clean building extract none of this is needed, and we do not add cost that the duty does not call for.
Roof fans are usually low-pressure. Why engineer them at all — can't I buy a standard unit?
You can buy a standard unit, and for a plain low-static building extract it may be fine. We add value where the standard unit stops: a specific flow and discharge configuration set to your re-entrainment case; a real sound target over occupied space; corrosion-resistant, FRP or stainless construction for coastal or process air; spark-resistant or ATEX build on fume and grease; and a documented weatherproofing scope. The duty is low static, but the environment — weather, noise, ignition and corrosion — is where a fan fails. We engineer for that and put every choice on a GA drawing you sign, made to order rather than pulled off a shelf.
What size and pressure range do your roof / wall exhaust fans cover?
Most roof and wall exhaust duty is low-static and high-flow — typically 10 to 250 mmWC against flows up to 2,00,000 CMH — and sits comfortably inside our full envelope of 2,00,000 CMH, 2,000 mmWC, 400 HP and 600 °C. Static rises toward 2,000 mmWC only where a filter, scrubber or a long stub duct is in the path. If your duty is beyond the envelope we engineer to spec and quote on enquiry. Every fan is sized to your exact operating point on our fan-selection software, not picked from a size table.
What construction do you use for coastal or corrosive process air?
The material follows the air and the exposure. For a normal roofline we use a spun aluminium or fabricated mild-steel weather hood with an epoxy or polyester powder coat. On a coastal site, a wash-down area or mildly corrosive extract we move to stainless steel and an IP66 motor. For aggressive process fume — acid, solvent or chemical-plant extract — we build in FRP or add a corrosion-resistant lining. We size the material and the coating to your air analysis and site exposure, not a default, and state it on the GA drawing so there is no ambiguity at the roofline.
Are your fans AMCA certified, and what about CE and ATEX?
To be precise about the claims: our fans are performance-tested in-house to the AMCA 210 / ISO 5801 method on our 200 HP VFD test rig — that is testing to the AMCA 210 method, not an AMCA certification, and we are not an AMCA member. Spark-resistant construction is built to AMCA 99. CE is self-declared per the relevant EU directives, and ATEX Zone 2/22 is self-declared per 2014/34/EU, Category 3, where the area classification calls for it — those are self-declarations of conformity, not third-party certifications. Our only third-party certification is ISO 9001:2015. Every fan is dynamically balanced to ISO 21940 G6.3 as standard, G2.5 or G1.0 on application, and bearing life is a design target of L10h at least 40,000 hours continuous.
