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What a fit-out does to the air, and what to check before it is signed off
Tick what is changing on the floor. The list on the right is what we would want looked at before the partitions are closed up — and what applies to every fit-out whatever is on the drawing.
The check
This is a prompt list, not a design. It does not size equipment, it does not calculate a load, and it is not a code review. It is what a mechanical contractor would ask on a walk-round, written down so you can ask it yourself.
What to look at
Nothing ticked yetTick something on the left and the list fills in. Nothing here is specific to your building until somebody has stood in it.
- The return air path. Supply is easy to see and returns are not. A new wall across a floor that returns through the ceiling void can cut a room off from its return entirely. Check where the air is meant to get back to, not just where it comes in.
- Diffuser positions against the new plan. A diffuser that ends up half over a partition head, or inside a cupboard, stops being a diffuser. Overlay the reflected ceiling plan on the new partition layout before anybody orders grid.
- Which thermostat now controls what. After a re-partition the sensor is frequently in a different room from the one it is supposed to be reading. Check every zone against the new plan.
- Outdoor air per person. More people on the same equipment means less fresh air each. Measure what the space is delivering in occupied mode rather than assuming the original design figure still applies.
- Whether the cooling has headroom. People, screens and lights all add heat. This is the point at which a rough load check is worth paying for — before the desks are ordered, not in the first warm week.
- How the rack room loses its heat when the building is off. Racks run at night and at weekends. A room cooled only by the building's system will climb as soon as that system goes to setback.
- Whether the rack room has its own alarm. A temperature alarm that reaches somebody is worth more than a larger unit with nobody watching it.
- Extract, and where the make-up air comes from. A kitchen extract with no deliberate air supply pulls it from wherever it can — usually under the entrance door and past the reception desk.
- Whether anything in the space burns fuel. Extracting from a room that also holds a flued appliance can pull the flue backwards. Where that is possible, it must be checked with the appliance running and the extract at full.
- Access to everything above the ceiling. Filters, coils, valves, dampers and fire dampers all need to be reachable afterwards. A ceiling without access panels turns a half-hour service into a half-day.
- The void depth the ductwork actually needs. Dropping a ceiling by 200mm is a cheap decision on a drawing and an expensive one when a duct has to be re-routed around it.
- The control schedule. If the floor is used at different hours, say so in writing to whoever holds the controls. Occupancy schedules are the cheapest change on this list and the one most often forgotten.
- Whether out-of-hours use has a cost attached. In a multi-tenant building, running plant outside core hours is often billable. Worth knowing before the lease is signed rather than after.
- Solar gain on the new elevation. South and west glass in Bellevue puts real heat into a room from spring onwards. The zone behind it may need its own control rather than sharing with the core.
- Whether the perimeter zone still matches the glazing. Zoning drawn around the old facade rarely survives a change to the glass line.
- Pressure between the process area and everything around it. Which way should the air move at the door? Decide it deliberately, because it will be decided accidentally otherwise.
- What the process actually puts into the air. Heat, moisture, fumes and dust each need a different answer, and some of them are not ours to solve — we will say so plainly rather than fitting a fan and hoping.
On a single packaged unit: one unit serving a whole floor has one supply temperature for everybody. Once a floor is cut into rooms with different uses, that becomes the limiting factor, and no amount of balancing fully fixes it. Worth knowing before the partitions rather than after.
On VRF or splits: you have room-by-room control, which helps — but each indoor unit was placed for the old layout, and outdoor air is usually a separate system that nobody thinks about during a fit-out. Check both.
On a central air handling unit: the part you can change is usually only the terminal equipment and the zoning. Anything involving the quantity of air reaching your floor is a conversation with the building, and it is a slow one. Start it early.
Not sure what serves it: that is normal in a re-let space, and it is the first thing to establish. A walk-round with the ceiling open in two or three places usually settles it in an hour.
- Get the air balanced after the work, with the figures written down — not before, and not "when someone complains".
- Find out who is responsible for fire dampers in any new wall that crosses a duct. It is a question with a legal answer, and it is not ours.
- Keep one drawing that shows what was actually built, not what was drawn in week one.
What this check is not
- Not a load calculationSizing equipment needs a proper calculation from the building fabric, the glazing, the occupancy and the internal gains. Nothing on this page replaces one.
- Not a code or permit reviewVentilation rates, fire dampers, combustion air and permits are governed by code and by the authority having jurisdiction. Ask them, or ask a designer.
- Not a substitute for standing in the roomEvery useful thing we have ever said about a floor came from opening a ceiling tile and looking.