When you are considering buying a ductless fume hood vs ducted fume hood what major things should you consider? Installation costs play a large role, as well as unit functionality, safety, and operational costs. Believe it or not, clean air systems are one of the largest expenditure’s lab managers face. So which is the better option and what do the numbers say?
What's The Difference Between A Ductless Fume Hood VS Ducted
Before we dive into the numbers, let's look at a couple of definitions to understand the difference between these two systems.
Princeton University defines a ducted fume hood or ducted exhaust hood as: "...a ventilated enclosure in which gases, vapors and fumes are contained. An exhaust fan situated on the top of the laboratory building pulls air and airborne contaminants through connected ductwork and exhausts them to the atmosphere."
ESCO Global defines ductless fume hoods, sometimes called carbon-filtered enclosures or filtered fume hoods as:
"...ventilation devices which exhaust chemical fumes, vapors, gasses, dust, mist and aerosols. ... However, unlike conventional fume hoods, ductless fume hoods filter out chemical fumes using activated carbon filters and recycle the air directly back to the working environment."
The Numbers
A study performed by Ellensweig Architects in collaboration with BR+A Consulting Engineers, R.W. Sullivan Engineering and Vanderweil Engineers; looked at the cost variations between these two types of units. They compared both the installation costs and the operating costs. Below we see the average one-time cost of installation for a ducted VAV fume hood compared to a ductless fume hood:
Ducted fume hoods take conditioned inside air and exhaust it outside. This requires new air be brought in and conditioned to room temperature in order to replace the air being pumped out. On hot or cold days, the conditioning of this “make-up air” can cost a significant amount money. Ductless hoods on the other hand filter the air and then recirculate it in the room, requiring no make-up air. As you can see below, this has a substantial effect on yearly operating costs.
Additional Considerations: Ductless Fume Hood Vs Ducted
Ducted Fume Hood
By design ducted systems give you the ability to work with a broad range of chemicals. Because the air is pushed outside, via the HVAC system, there is little risk of hazardous particulate recirculation. However, being attached to the facilities HVAC system will also require you to work around HVAC maintenance schedule. This can mean shutting down anywhere from 1 to 4 times a year for maintenance. Ducted systems are also generally stuck where you install them. When a lab redesign occurs, this piece generally remains in the same place. This is because it can quickly become cost prohibitive to move due to it being tied into the HVAC system.
Ductless Fume Hood
Ductless systems can come in at a lower installation price and also a lower annual operational cost. So why would you ever choose a ducted system? Depending on the chemicals being used you may be limited by the filter in a ductless unit. A HEPA filter that captures up to 99.97% of particles may not be enough if the chemicals being worked on are particularly harmful. That means that .03% are recirculated into the lab. This could have a harmful effect depending on exposure times and which chemicals you are working with. Also, if you are working with a large variation of chemicals (say more than 10) a ductless system may become more impractical. This is because filters may need to be changed based on the chemicals being used. Filter maintenance is also much more important when using a ductless system. This often means that the system may require a filter change once every 6 months or yearly depending on the set up. Particular attention to filter type becomes important because there are different filters for different chemicals.
Common Ductless Fume Hood Filters Include:
- ASHRAE Filter: up to 95% efficient on particles down to 0.5 microns
- HEPA Filter: up to 99.97% efficient on particles down to 0.3 microns
- ULPA Filter: up to 99.9995% efficient on particles down to 0.12 microns
- Activated Carbon Filters: Efficiency varies
Safety And Advances In Technology
The redundancy built into ductless system makes them safe for many applications. Built in filter saturation alarms protect against chemicals being emitted in the recirculated air and back-up filters protect against filter malfunctions. Ducted systems can be great when highly toxic chemicals are being used or where the system needs to be in constant use.
Talk with the experts at Balcon if you need help making the right decision for your lab. The pro’s and con’s of a ductless fume hood vs ducted hood need to be weighed carefully. The right decision will depend on your specific lab set up.
Give us a call at (712)-309-3680. For over 25 years, BalCon’s Lab Safety Services Team has been ensuring the safety of people, equipment, and lab environments. By exceeding all national standards, our Lab Safety group is the leader in comprehensive testing, certification and service.
