Ducted or ductless fume hood for a Singapore laboratory?

A ducted hood exhausts the air, and everything in it, to the outside through a duct and fan, so it does not depend on a filter to protect the operator and can handle a very wide range of chemicals. It needs a route to the roof or facade, a make-up air supply and a fan that stays in balance with the rest of the building. A ductless hood passes the air through an activated carbon or combined filter and returns it to the room, which makes it easy to install in a leased or renovated space and avoids the energy cost of expelling conditioned air. Its limit is that the filter must be matched to the chemicals in use and must be changed before breakthrough, so it suits low-volume, known chemistries such as acid digestions, staining or solvent handling. In Singapore, where cooling load matters, many labs use ductless hoods on light duties and reserve ducted hoods for high-volume or highly toxic work; whichever you choose, the selection must be based on the chemicals, the quantities and the exposure limits, not on installation convenience alone.

What face velocity should a fume hood run at?

The conventional working range is 0.3 to 0.5 metres per second, measured at the face of the hood with the sash at its normal operating height. Below about 0.3 m/s the hood may not capture fumes reliably, particularly with draughts from doorways, air-conditioning diffusers or the operator moving past the opening. Above about 0.5 m/s the airflow becomes turbulent, which can pull contaminants back out of the hood, and the fan energy and noise rise sharply. The correct figure depends on the hood type, the sash position and the hazard of the work, so the setpoint should come from the manufacturer and be confirmed by measurement. Test with a calibrated anemometer across a grid of the face opening rather than a single reading, log the result, and re-test after any change to the duct, fan, room layout or building air balancing.

How often should fume hood filters be replaced?

A filter change is driven by loading, not by the calendar, so use the schedule in the manual as a backstop and let measurement lead. Activated carbon filters should be changed at a defined fraction of their rated capacity, typically when laboratory monitoring or the manufacturer's service indicator shows approaching breakthrough, and always when any odour is detectable at the face. In practice a busy bench using solvents may need a change within a few months while a light-use teaching hood may go a year or more. HEPA filters are changed when the pressure drop across them rises beyond the manufacturer's limit or when a particle challenge test shows penetration. Every change must be logged with the date, filter part number, the chemicals the hood has seen and the measured face velocity afterwards, and the used filter must be bagged and disposed of as chemical waste. Never extend a filter's life to save cost on a hood handling toxic or carcinogenic material.

What filters and ducting does JWRESEARCH supply in Singapore?

JWRESEARCH supplies fume hood filters and ducting components for laboratories across Singapore, including activated carbon filter cartridges, combined carbon and HEPA cartridges, pre-filters, filter housings and seals, ducting in the common diameters, flexible and rigid duct sections, bends, reducers, dampers and roof cowls, together with anemometers and service accessories for face velocity checks. We stock cartridges to suit the widely used benchtop and ductless hoods and can source specific chemistries to order. Orders are dispatched locally in Singapore, with volume pricing for schools, industrial laboratories and facilities teams that maintain several hoods.

Fume Hood Filters and Ducting Singapore

Published: {{NEW_ARTICLE_DATE}} | By JWRESEARCH | Category: Laboratory Equipment

A fume hood is only as good as the air path through it. The sash, the baffles and the worktop get the attention, but the filter and the duct do the actual protecting, and a hood that is overdue for a filter change can look perfectly normal while doing very little.

At JW RESEARCH SUPPLY, we supply fume hood filters, carbon and HEPA cartridges, ducting components and face velocity instruments to laboratories and facilities teams across Singapore. This guide sets out the filter types, the numbers that matter and the maintenance schedule.

Filter Types Compared

Filter Type	Removes	Typical Application	Change Trigger
Activated carbon	Organic vapours and solvents	Solvent handling, staining, extractions	Breakthrough or odour at face
Impregnated carbon	Acid gases, ammonia, formaldehyde	Acid digestions, histology, formaldehyde work	Breakthrough or rated capacity
HEPA	Particulates, powders, aerosols	Powder weighing, microbiology, nanoparticle work	Pressure drop limit or penetration test
Combined carbon + HEPA	Vapours and particulates	Mixed chemical and powder procedures	Either element at limit
Pre-filter	Coarse dust, lint, aerosols	Protects the main cartridge	Visible loading, monthly to quarterly

Specification Reference

Parameter	Typical Value	Notes
Face velocity	0.3 – 0.5 m/s	Measure at the sash opening with an anemometer
Sash working height	200 – 300 mm	Lower sash improves containment
Duct diameter	150 – 250 mm	Match to airflow and run length
Duct material	PVC, PP or coated steel	Choose for the chemicals exhausted
Carbon bed depth	50 – 100 mm	Deeper beds give longer life
Filter pressure drop	50 – 250 Pa	Rising drop signals loading

Ducted versus Ductless

A ducted hood exhausts to atmosphere and does not depend on a filter, so it can handle almost any chemistry, but it needs a duct route, make-up air and a balanced fan. A ductless hood recirculates filtered air into the room, which is far easier to install in a leased or retrofitted space and avoids expelling cooled air, but it is limited to the chemistries its filter can hold and to the volumes the bed can absorb.

The decision should follow the chemistry, not the installation cost. High-volume solvent work, perchloric acid, and any process that produces a large or unknown mixture belong on a ducted hood. Light, known duties such as small acid digestions or staining can run on a ductless unit with a correctly matched cartridge and a disciplined change schedule.

Duct Design Points

Keep the run as short and as straight as possible; every bend costs airflow
Balance the exhaust against the room's make-up air so the hood does not starve
Choose duct material resistant to the chemicals being exhausted
Fit a damper and, for long or shared runs, a fan sized with margin
Terminate above the roof with a cowl that prevents rain ingress and downdraught
Never connect a fume hood to a general ventilation duct or a toilet exhaust

Maintenance and Testing

Check face velocity with a calibrated anemometer across a grid of the sash opening and log the result. Test containment with a smoke source at the worktop, watching for escape at the sash edges. Inspect the sash cords, counterbalance, baffles and interior surfaces for corrosion or residue, and check the airflow monitor and alarm if the hood has one. Replace the pre-filter when it is visibly loaded, and change the main cartridge on breakthrough, pressure drop or the rated capacity, whichever comes first.

Every change should be logged: date, part number, the chemicals the hood has handled, the measured face velocity afterwards and the disposal route for the used filter. That record is what shows a safety inspector, or an auditor, that the hood has been maintained rather than merely present.

Ordering Checklist

Hood make and model, or the cartridge part number if known
The chemicals and approximate volumes handled per week
Filter type needed: carbon, impregnated, HEPA or combined
Duct diameter, run length and material if ducting is required
Face velocity instrument and a spare pre-filter set
Replacement interval and who will hold the consumable stock

Send us the hood model and the chemistry list and we will match the cartridge, quote the ducting and set a sensible replacement interval so the hood stays in specification between services.

Contact JWRESEARCH

JW RESEARCH SUPPLY — laboratory equipment and consumables, Singapore.
Telephone / WhatsApp: +65 8039 3660
Email: SINGAPORE@JWSHY.COM
Website: www.jwresearch.cn