Fume hood buying guide: sizing, ducting, testing and the costs the quote leaves out

The decisions that set the price

1. Ducted or filtered. A ducted hood exhausts outside and needs a fan, a duct route and make-up air. A filtered or ductless hood carries its own carbon or particulate filtration and needs none of that, but it is only suitable for a known and limited chemical inventory, and the filters are a recurring cost with a monitored breakthrough point.
2. Bypass, restricted bypass or variable air volume. The airflow scheme decides how much conditioned air the hood throws away when the sash is down. Variable air volume costs more to install and much less to run, which usually decides it for a new building and rarely decides it for a single replacement hood.
3. Width, depth and interior services. Hood width is chosen from the work, not the space, and every service dropped into the interior, gas, vacuum, water, electrical outlets, is a separate line and a separate penetration. Decide the interior layout before the order rather than during the installation.
4. Liner and worktop material. Epoxy resin is the general-purpose liner; stainless steel suits radionuclide and perchloric work, and polypropylene suits hydrofluoric acid. A liner chosen for price and not for chemistry is replaced early, and replacing a liner means taking the hood out of service.
5. Commissioning and the containment test. The hood is not usable until face velocity is set and a containment test has been performed as installed, with the room's air balance as it will actually run. Confirm who performs that test, when, and what happens if the result fails.

What the quote for an exhaust fume hood usually excludes

Expect the hood manufacturer to quote the enclosure, the base cabinets, the liner and the interior services, and nothing beyond the connection point. The exhaust fan, the duct run, roof penetration and weatherproofing, the make-up air provision, the control system, the electrical work, the plumbing and the commissioning are a construction project.

Ask early whether the building's existing air handling can supply make-up air for another hood. A replacement hood in an existing bench run is usually straightforward; an additional hood frequently is not, and that answer changes the budget by an order that has nothing to do with the model chosen.

Running cost of ducted fume hoods, and ongoing testing

A ducted hood exhausts conditioned air continuously unless it is a variable air volume design with a working sash sensor, and in a heating or cooling climate that is the dominant lifetime cost. Sash discipline matters more than any specification decision: a hood left open at full height throws away air all night.

Periodic face velocity checks and a documented containment test after any change to the room's air balance are what keep the hood a control rather than a cupboard. Build that into the service contract at purchase, when you have leverage.

The enclosure is a fraction of the cost

The quoted price is for a box. What makes it work is ductwork, a fan sized for the system, a control system, make-up air for the room, electrical work, commissioning and a containment test, and in most installations those cost more than the enclosure.

Ask for a delivered and commissioned price with the extract system included, or price the building work separately before comparing enclosures. A comparison between two quoted enclosures tells you very little about what the installation will cost.

Capture hoods are not containment

An open canopy above a process, or an articulated arm brought close to a source, captures what rises or what is released within a short distance, and nothing else. They suit a known, localised, low-hazard release and they do not contain a spill or a reaction that runs away.

Their advantage is that they can be added to an existing room cheaply and moved. Their limitation is that capture falls off sharply with distance, so they only work when the operator keeps the source close, which is a habit rather than a safeguard.

Filtered enclosures, and the limits of the media

A recirculating enclosure with a carbon or particulate filter needs no ductwork and returns air to the room, which makes it attractive and constrains it: the filter must be matched to the chemistry, it saturates, and it has to be monitored and changed on evidence rather than on hope.

They are appropriate for known, listed chemicals in small quantities, with a maintained log and a monitoring arrangement. They are not appropriate where the chemistry varies, where quantities are significant, or where a breakthrough would be discovered by someone smelling it.

The fume hood monitor, the fume hood exhaust fan and the parts that come later

An airflow monitor at the sash is the only thing that tells an operator the enclosure is working, and it is regularly value-engineered out of an order. Specify it, and specify an audible alarm rather than a light nobody looks at.

The fan is part of the system rather than an accessory: it has to be sized for the duct run, sited so the duct is under negative pressure inside the building, and made of a material the exhaust will not attack. Where the chemistry is corrosive, the fan and the duct material are a specification, not a preference.

laboratory fume hood manufacturers and the specification to send them

Asking laboratory fume hood manufacturers for a price needs the specification first: face velocity, the containment test method the hood must meet, the liner material for the chemistry, the services required and whether it is ducted or filtered. Without that a quote is a cabinet rather than a hood, and containment is what a hood is bought for.

Common questions

What is the difference between a fume hood and a biosafety cabinet?

A fume hood protects the user from chemical vapour by drawing air away and exhausting it. A biosafety cabinet protects the user, the sample or both using filtered air, and many recirculate. They are not interchangeable: a fume hood offers no product protection and a cabinet offers limited chemical protection.

Do ductless fume hoods work?

For a defined and limited chemical inventory within the filter's capability, yes, and they are far cheaper to install. They are unsuitable for unknown or varied chemistry, for large volumes and for anything the filter medium does not retain, and they need a monitored filter change regime.

How is a fume hood tested?

Face velocity across the sash opening is measured at commissioning and periodically afterwards, and a containment test using a tracer is performed as installed. A hood that has never been tested as installed in its own room has not been proven to contain anything.

What size fume hood should I buy, and when is a benchtop fume hood enough?

Size it from the largest apparatus you will put in it plus working clearance, then check the room can supply the exhaust. Buying a wider hood than the air handling supports is the most expensive way to discover a building limit.

Is a second-hand enclosure a sensible buy?

Only with the extract system it will be connected to. The enclosure is the cheap part, and its containment performance depends on ductwork, fan sizing and commissioning. Budget a containment test as installed, whatever its history.

Does a capture arm replace an enclosure?

No. It captures what is released close to it and does not contain a spill or a runaway reaction. It suits a known, localised, low-hazard release where the operator keeps the source within a short distance.

Browse by service class

• Compare Gene synthesis on advertised prices