Under Floor Air Distribution (UFAD) Issues and Problems

UFAD Cutaway DiagramI am re-posting a response I gave in a message forum that I have begun to frequent recently, HVAC-Talk.com.  The original poster is the building owner’s representative for a library facility which is due for a major renovation and his concerns were with his design and engineering team.

 I’m currently involved with the design phase of a multi-story, 200,000 square foot, library (I am the “building owner”) in which the design team is pushing heavily for a UFAD system throughout the building (design team is trying to accomplish LEED Platinum and is more interested in the design awards they’ll receive as a result than delivering a design that is truly sustainable, IMHO).

I can totally understand that. Seems the highly paid engineers are always looking for that next project that they can frame and put on their wall and resume. The following info may sound like a rant, but really I am just throwing out some CONS or possible issues with using a UFAD system. I am in no way an expert in UFADs, but to me these points just plain make sense to me.

My general feelings are: “Going GREEN seems to always cost alot of green.”

With Under Floor Air Distribution (UFAD) the biggest problem as seen with its implementation in recent GSA buildings is…


Air Leakage

UFAD Ssmoke Test Air LeakThere are two types:

  • Category 1 – Air leaks from the plenum supply air to non-conditioned non-plenum areas.
  • Category 2 – Air leaks from the plenum supply air to the conditioned space.

These cause numerous issues including, loss of energy due to higher fan speeds and need for additional cooling. The coordination involved for an airtight construction involved literally 10-12 various trades trying to all work together to find where the smoke from the smoke test is coming from (read as GOOD LUCK!).

A better fix to this is to use a fully ducted underfloor system. This could definitely assist these air leakage probelms, but … what happened to all that money save by not having to install ductwork???


Under your nose… er feet even.

Let’s talk about that plenum… once that is sealed up what all do you think finds its way in there? Dust, dirt, water from condensate of the slab metal fixtures, drainage of leaky pipes or fire piping discharge. Not to mention just some loss of thermal energy of the huge concrete slab.


“You know I really want those desks… shelves… cubes… moved over there.”

Moving Library ShelvesI know you said you had a Library facility and thought the book shelves may not move much there are alot of other things that will and moving floor vents and electrical connections is not easy once the system is under pressure and working. Once you lift a tile to do some work you are losing static pressure for the whole system.

Also access to all the connections and equipment in the floor once furniture and other fixtures are in place can really cause a headache. Usually these types of installations that aren’t in a sever room or big open space get covered up with carpet so it is also another issue for accessing the underfloor areas easily.


“Trust me… It’s working properly.”

Air Balance Hood - Testing and CommissioningSo your engineering team is all sparkles in their eyes and talking about UFADs and unicorns, rainbows and lollipops. Well who is going to be commissioning and testing this system? Do they have previous experience with UFAD systems? Does your engineering team have other UFAD projects under their belt?

As far as I know and correct me if I am wrong… UFADs don’t have very solid if at all, documented testing and commissioning procedures in place by writing authorities. Not sure maybe this has changed in the last 2 years.


With that being said, I’m trying to get as much information as possible to defend against this design recommendation and be able to present a viable arguement FOR a traditional overhead design, unless I can be convinced a UFAD system is actually a better fit for my application.

I think you are doing a great job of investigating further, but I am sure you should probably get a second opinion from some PE rather than trusting some fool who calls himself “The Controls Freak” on a public message forum. LOL

Honestly, I think UFADs have some good qualities and I have dealt with several in non-people areas like server rooms and large open warehouse spaces. I just don’t think they really pay off for spaces that are more flexible, meaning spaces where fixtures and occupancy change more often.

And as a final note… Long ago I found out I hate to be the Guinea Pig. If I was the building owner I would seriously be looking for previous work and calling those owners and managers with UFADs and asking them what they think. Seriously!

Call up your Building Owners and Managers Association (BOMA) and start asking for people who have a UFAD system, that isn’t in a server room and ask them what they think and what they have experienced.

Just did a quick Google: ” UFAD poor performance ” Mitigate the risks my friend and maybe it will work for your building.


…and that is “The Controls Freak-speak.”

One Response to Under Floor Air Distribution (UFAD) Issues and Problems

  1. Richard Cortner November 29, 2011 at 23:35

    Wohh precisely what I was searching for, thanks for putting up.


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