Picking equipment without a load figure is guesswork. Plenty of projects still size everything on a spreadsheet, copying areas off the drawings, and copying them again after every architectural revision.
The Revit model already holds the areas, the volumes and the orientation, so heating and cooling loads in Revit simply read back what you have modelled. This article walks through the whole workflow on Revit 2027, the release that reworked zoning: HVAC Zones became System-Zones and the loads dialog was rebuilt. To learn the whole HVAC workflow on a real building, see the Revit MEP course.
What Revit calculates the loads with
Autodesk states it on the Heating and Cooling Reference page: the feature follows the ASHRAE Handbook of Fundamentals and finds peak loads with the RTS, the radiant time series method.
A revit cooling load figure is the end of a chain of four stages. Miss one and everything after it breaks.
| Stage | What carries the data | Where you set it |
|---|---|---|
| 1 | Space — area, volume, occupancy, lighting and equipment loads | Analyze › Spaces |
| 2 | System-Zone — the spaces served by one unit, one control point | Analyze › Zoning |
| 3 | Energy model — the analytical model Revit builds | Analyze › Energy Optimization |
| 4 | Loads report — figures by building, level, zone and space | Analyze › Reports & Schedules |
The project location and its weather data sit outside those four stages but decide every number: the same building in Hanoi and in Boston returns two very different results.
Before you start: spaces and the sample file
Spaces come first. The article on spaces in Revit MEP covers room bounding for the linked architectural model and placing spaces across a floor; the Revit MEP sample file gives you a file to follow along with.
Three things to check first, all three stated in Autodesk's own documentation. Spaces must cover every area, ceiling voids and shafts included. Spaces and system-zones must sit in the open file, not in a link. The phase of the spaces must match the phase of the project.
System-Zones replace HVAC Zones: four changes in Revit 2027
Anyone trained on 2024 or 2025 will look for the HVAC Zones button on the Analyze tab and not find it. Autodesk's What's New pages list the changes.
| Item | Revit 2026 and earlier | Revit 2027 |
|---|---|---|
| Name and tools | HVAC Zones, a single Zone button | System-Zones, two buttons — By Space and By Sketch — on the Zoning panel |
| Default zone | Every project carried a Default zone that new spaces fell into | No default zone at all; a new project starts empty |
| Opening an older project | — | Old zones convert to system-zones with a type that marks their origin; some parameters are renamed or dropped |
| Enabling the loads tool | Some releases needed a Revit.ini edit before the button appeared | That Revit.ini switch is gone |
The practical consequence of the second row: from 2027 a space belongs to no zone until you put it in one. Grouping spaces into system-zones is mandatory, not cosmetic.
The steps: location, settings, zones
Step 1. Open the plan of a level that already has spaces. Check them quickly in a space schedule: no row should read Not Placed or Not Enclosed.
Step 2. Run Analyze › Energy Optimization › Location. The Location and Site dialog opens with a Location tab and a Site tab.
Step 3. Leave Define Location by on Internet Mapping Service, type the address into Project Address — Hanoi, Vietnam in the screenshots — and click Search. The map jumps to the site, latitude and longitude change, and Weather Stations lists the nearest stations with their distance.
Step 4. Pick the station closest to the site and click OK. That station supplies the summer and winter design temperatures.
Step 5. Run Analyze › Energy Optimization › Energy Model Settings. The button carries a drop-down with two entries: Energy Model Settings and Energy Model Guide, the step-by-step wizard added in 2027.
Step 6. In the Energy Model Settings dialog, switch Mode to Spaces. The dialog shortens to the settings that matter in that mode: Project Phase, Ground Plane, Building Type, Material Thermal Properties and Advanced Setting.
Step 7. Set Ground Plane to the level in contact with the ground and Building Type to the closest match for the project, then click Save. Building type drives the default operating schedule and the default load densities.
Step 8. Run Analyze › Zoning › By Space and click the spaces that belong together. Properties shows the type Zone: System-Zone, a Level Offset of 1200 mm by default, the area, volume and perimeter updating as you add spaces, and an Energy Analysis group with Zone Equipment.
Step 9. Click the green tick, Finish Editing Zone, on the Mode panel. The zone appears in plan as an outline around the spaces you picked.
Step 10. Repeat for the other zones. Where the split does not follow walls — a large open office divided into a core and four orientations, say — use By Sketch: draw a closed shape and every space inside it or touched by it joins the zone. A zone drawn this way is a Sketch-Based System-Zone, and Properties reports the area it has gathered.
Running the heating and cooling loads in revit analysis
Step 11. Run Analyze › Reports & Schedules › Heating and Cooling Loads.
Step 12. If the project has no analytical model yet, Revit asks first with the Energy Analytical Model Required dialog, warning that building one can take a significant amount of time and that Revit will not be accessible meanwhile. Click Create the Energy Analytical Model and continue to run the analysis.
Step 13. The Heating and Cooling Loads Analysis dialog opens. Revit 2027 lists the three preparatory jobs at the top, then four settings.
| Setting | What it does | Value in the sample |
|---|---|---|
| Building Service | The system serving the building | VAV - Single Duct |
| Building Infiltration Class | Air leaking through the envelope: Loose, Medium, Tight or None | None |
| Report Type | Level of detail: Simple, Standard, Detailed, Compact | Standard |
| Use Load Credits | Allows negative loads, heat crossing into a neighbouring zone for example | cleared |
Step 14. Click Run Analysis and wait for the heating and cooling loads in Revit to be calculated. When it finishes, Revit opens the report view straight away, and the report also sits in the Project Browser for later. On later runs, with an analytical model already in the file, Revit asks through the Energy Analytical Model Already Exists dialog whether to use the existing model or to Update Energy Analytical Model and rebuild it from the edited model.
Reading the loads report
The report is split into sections, and it opens with Project Summary.
Step 15. Read Project Summary first, because it tells you which weather data the run used. With a Hanoi address it reads latitude 21.03°, longitude 105.85°, summer dry bulb 35 °C, summer wet bulb 25 °C, winter dry bulb 11 °C and a mean daily range of 11 °C. If those four figures are wrong, everything below them is wrong too.
The sections that follow go from the whole building down to the single space.
| Section | What it gives |
|---|---|
| Building Summary | Area and volume of the building; peak cooling load with the month and hour it occurs; sensible and latent load; maximum cooling capacity; peak airflow |
| Checksums | Load and flow per unit area — a few numbers for a quick sanity check |
| Level Summary | The same items, level by level |
| Zone Summary | Per system-zone, with set points, supply air temperature, occupancy and infiltration |
| Space Summary | Per space |
Building Summary is the one to read first. On a sample office building it comes back with 42,757 SF of area, a peak cooling load of 523,417 Btu/h at 11 a.m. in September, 494,496 Btu/h sensible, 28,921 Btu/h latent and a maximum cooling capacity of 676,252 Btu/h.
Units follow the Project Units of the file, so a metric project reports W, m² and L/s instead of Btu/h, SF and CFM.
The checksums deserve the longest look, because one number tells you whether the result is plausible. Zone Summary then shows the set points each zone is running on.
A room coming back at several times the load density of its neighbours usually means the space has the wrong occupancy or the wrong space type, not that the building is unusually hot.
From the spreadsheet to Revit
Hand calculations still have their place, but their slowest part is data entry, and that is exactly what the model does for you.
| Job | Spreadsheet | Revit 2027 |
|---|---|---|
| Room area and volume | Copied off the drawings | Spaces compute it and follow architectural changes |
| Orientation and solar gain | Looked up by facade | Taken from the model and the project coordinates |
| Design temperatures | Looked up in a standard | Taken from the nearest weather station |
| People, lighting, equipment | Typed room by room | From the space type, editable per space |
| Testing an option | Rebuild the sheet | Run the analysis again |
What Revit does not do for you: choosing design parameters to your local standard, and deciding the safety margin. The output is data for an engineer to read, not a decision made on the engineer's behalf.
When the loads report comes back empty
| Symptom | Cause | Fix |
|---|---|---|
| The run finishes but area and loads are all zero | The analytical model picked up no spaces. Mode in Energy Model Settings is not Spaces, spaces belong to no system-zone (2027 has no Default zone any more), the zone has Zone Equipment set to Unconditioned, or spaces exist on one level only and every boundary comes from a linked model | Set Mode to Spaces, leave Zone Equipment on <None>, cover every space with a system-zone, place spaces on every level to be analysed, then choose Update Energy Analytical Model and run again. Still zero: check Autodesk's Heating and Cooling Loads Analysis pages |
| Energy Analytical Model Required appears on every run | The analytical model was never finished, or a model change invalidated it | Click the command link and wait; do not touch Revit while it builds |
| Design temperatures look nothing like the local climate | The project address is still the default one | Set the address again and pick the nearest weather station |
| No HVAC Zones button | 2027 renamed it | Use Analyze › Zoning › By Space or By Sketch |
| One space ends up in two zones | A sketched zone touches the neighbouring space | Redraw the sketch, or use By Space to be safe |
| Results do not change after a model edit | You are reading the old report | Run the analysis again; every run writes a new time-stamped report |
Three things people often get wrong:
| What you often hear | What Revit 2027 actually does |
|---|---|
| A model is enough to get loads | You need spaces, system-zones, a location and weather data before anything runs |
| You must edit Revit.ini to see the tool | 2027 dropped that switch; the button sits on Analyze › Reports & Schedules |
| The report replaces the engineer's calculation | The report is an input to check against; the engineer still picks design parameters and margins |
Frequently asked questions
Where did HVAC Zones go in Revit 2027?
They became System-Zones. Create them with Analyze › Zoning › By Space or By Sketch. Older projects convert their zones on upgrade.
Does the calculation need an internet connection?
Only the location step does, because the map and the weather station list come from an online service. The load calculation itself runs on the machine.
Can the report be exported to a spreadsheet?
The report is a view inside the project and has no export button. For tabular data, build a space schedule with the calculated load fields and export that, as covered in schedules in Revit.
How is this different from Systems Analysis?
Heating and Cooling Loads gives peak loads for sizing equipment. Systems Analysis runs an annual energy simulation, needs analytical systems built on top, and answers consumption and carbon questions.
Do ceiling voids need spaces too?
Yes. Autodesk recommends placing spaces in every area, voids and shafts included, so that internal walls are not treated as exterior ones.
Related articles
- Spaces in Revit MEP — the mandatory step before any load calculation
- What is Revit MEP — the three MEP systems in one model
- Revit MEP sample file — the file used in this walkthrough
- Schedules in Revit — getting space data into a table and into Excel