The AHU in the schedule is not the AHU in the model
A building services engineer updates the heating load calculation after the architect changes the glazing. The boiler and pump duties go up. The Revit model gets the new pumps, but the equipment schedule spreadsheet issued with the tender still shows the old duties. A contractor prices from the schedule and later queries why the drawings show something different.
On a large scheme there are hundreds of items: air handling units, fan coils, pumps, distribution boards, luminaires. Each change in the design has to ripple through calcs, model and schedule, and one of the three is always a step behind.
Why schedules fall out of step
- Sizing and load calculations run in dedicated tools whose outputs are not linked to the model.
- Model schedules exist, but many teams issue a formatted spreadsheet the contractor expects instead.
- Equipment references change as systems are renamed, breaking manual cross-checks.
- Several engineers work on the same systems, each updating their part.
- Late changes before an issue are made quickly and not propagated everywhere.
Deadlines amplify the problem. The final design changes before a tender issue always arrive in the last few days, when there is least time to cross-check. An engineer updates the pump duty in the calc and the model, means to update the schedule, and the issue goes out before they get to it.
What mismatched schedules cost
| Mismatch | Consequence |
|---|---|
| Duty in schedule differs from calc | Contractor prices or selects the wrong equipment |
| Item in model missing from schedule | Item left out of tender pricing |
| Quantities disagree | Queries, variations and lost confidence in the information |
| References inconsistent | Hard to trace items across documents |
Each query that comes back during tender or construction takes an engineer's time, and a pattern of them affects how contractors and clients see the practice's information.
How we build schedule checking
- We read equipment data from your model through the Revit API or a scheduled export, including type, reference, system and key parameters.
- We read calculation outputs from the tools you use, through their exports, and map them to equipment references.
- We read your issued schedule spreadsheets.
- The three are compared item by item, and a report lists every mismatch in duty, quantity, reference or location.
- Engineers resolve mismatches at the source, whether calc, model or schedule, and rerun the check.
- Once the check is clean, the issue schedule can be produced from the model data in your contractor-facing format, so it is not retyped.
- Checks can run before every issue, as part of the issue process.
Where calculation tools do not export in a usable form, we start with model against schedule, which catches a large share of problems on its own.
We usually start by comparing model and schedule on one recent project, which quickly shows how consistent your references are and where the mismatches tend to come from. That often leads to a small agreed referencing convention that makes every later check more reliable.
What issue day feels like afterwards
Before a tender issue, the engineer runs the check and works through a short list of mismatches instead of hoping nothing was missed. The schedule issued matches the model.
Contractor queries shift from 'which of these is right' to genuine technical questions.
Is this happening to your team?
- Contractors query differences between schedules and drawings.
- Schedules are maintained as separate spreadsheets.
- Duties change after calc updates and schedules lag behind.
- Nobody cross-checks model, calcs and schedule before issue.
- Equipment references differ between documents.