Revit HVAC load calculation: what Revit does, where it stops, and how to run loads alongside it

How to run HVAC load calculations from Revit: the Heating and Cooling Loads tool, Systems Analysis, gbXML to a load program, and add-ins.

TL;DR

Revit has two built-in ways to calculate HVAC loads. The older Heating and Cooling Loads tool uses the ASHRAE Radiant Time Series method, but since Revit 2022 it's hidden by default and has to be switched on in Revit.ini. The newer Systems Analysis (since Revit 2020.1) translates the energy analytical model to EnergyPlus through OpenStudio workflows and adds sizing loads as properties on analytical spaces. Both depend on a clean, space-bounded model. Most mechanical teams run design loads and ASHRAE 62.1 outdoor air in a dedicated tool (Carrier HAP, Trane TRACE, IESVE, Elite Chvac, or HVAKR) and bring airflows back into Revit spaces, either by gbXML import where the load program supports it or by entering values from the load report. HVAKR also has a free add-in for Revit 2025 and 2026 that round-trips MEP spaces between Revit and HVAKR, so you don't re-key the model.

How Revit models loads

Loads in Revit hang off spaces (MEP spaces placed inside the architectural rooms) grouped into zones. For Systems Analysis, Revit builds an energy analytical model with analytical spaces, and you can add analytical systems (air systems, zone equipment, water loops). Revit computes each space's analytical volume from the center planes of the bounding walls and the top planes of floors and roofs, and Autodesk tells you to use it to check the model for gaps.[1] In practice that means room-bounding elements and space upper limits have to be right before any load runs.

That last point is where most Revit load workflows break. A mechanical engineer usually inherits an architectural model that was built for drawings, not analysis. Gaps, unbounded spaces, and missing ceilings turn into wrong volumes and missing surfaces.

Option 1: Heating and Cooling Loads (the legacy tool)

• Method. Autodesk says the feature follows the ASHRAE Handbook of Fundamentals and adheres to the Radiant Time Series (RTS) method.[2]
• Status. From Revit 2022 on, the tool is disabled by default in the interface. Autodesk's fix is to add the line EnableHeatingAndCoolingLoads=1 under the [Misc] header in Revit.ini, save the file, and reopen Revit.[3]
• Autodesk's own view. Replying on the Revit Ideas forum in December 2022, Autodesk's Ian Molloy wrote that the original RTS heating and cooling loads "has a number of fundamental limitations, both in terms of in the inputs (esp. geometry), thermal calculation and outputs," and called Systems Analysis an "intended upgrade/future replacement" that is "zonal heat balance method based."[4]

Use it for a quick check on a simple model. Don't build a submittal around a tool its vendor hides by default.

Option 2: Systems Analysis (EnergyPlus inside Revit)

Autodesk introduced Systems Analysis in Revit 2020.1. It uses EnergyPlus and the OpenStudio SDK, with Revit data passed in gbXML form to build the model.[5] How it works today, per Autodesk's help:[6]

• Two default workflows: Annual Building Energy Simulation and HVAC System Loads and Sizing. A workflow is a script that translates Revit data to EnergyPlus, runs the simulation, and writes a report. You can write your own.
• If you haven't created analytical systems, Revit uses an ideal air system. Analytical spaces you don't assign to zone equipment also fall back to ideal air.
• The run happens in the background and produces a loads report and a detailed report. Sizing loads are added as properties to the analytical spaces at the end of the analysis.

What it's good for: early design, envelope and massing studies, energy comparisons, and a sanity check on equipment size, all without leaving the model. What to watch: results are only as good as the energy analytical model, default schedules and constructions, and system definitions; and the Autodesk help pages cited here don't describe Systems Analysis as documenting compliance with ANSI/ASHRAE/ACCA Standard 183 or producing an ASHRAE 62.1 ventilation schedule.

Option 3: A dedicated load program, connected by gbXML

This is how most commercial teams work: model in Revit, calculate in a load program, push results back.

• Trane TRACE 3D Plus imports a Revit gbXML (exported with the Space option) and, from version 7.0, can export room cooling load, room heating load, and the larger of the cooling or heating airflow back to Revit by gbXML. Trane warns that geometry changes made in TRACE after import aren't reflected in the Revit model.[7]
• Elite Chvac says it imports and exports gbXML.[8]
• Trane's next TRACE is a cloud-based application built for Revit integration in collaboration with Autodesk. Trane's March 2026 FAQ planned a 2026 rollout, starting with central plant energy modeling in spring and Preliminary Load Design in summer.[9] On October 28, 2026, Trane's TRACE page said a TRACE beta is available.[15]

The catch with any gbXML exchange: the model has to be space-bounded before export, and every architectural revision means export, re-import, re-check, and push back.

Option 4: Add-ins inside Revit

• Ripple offers free HVAC tools for Revit, funded by sponsors: one-button loads, ventilation, and zoning, plus diffuser layout, VAV selection through Price Industries' selection software, and AHU and plant selection. Ripple describes its automatic loads as "rule-of-thumb loads and airflows" built from ASHRAE 62.1 space type defaults and the project climate zone, and separately advertises "complete and accurate heating and cooling loads with a single click."[10] Check which mode you're running before you rely on it.
• HVAKR has a free add-in for Revit 2025 and 2026 that adds an HVAKR ribbon tab and round-trips MEP spaces between Revit and HVAKR, creating a new HVAKR project or updating a linked one. Loads are calculated in HVAKR. See "HVAKR's Revit add-in" below.

Revit's options side by side (as of October 28, 2026)

Sources: Autodesk help (H&C reference, Run a Systems Analysis, support article); Trane (gbXML KB, TRACE 3D Plus load method, support lifecycle); TRACE page); HVAKR docs. Checked Oct 28, 2026.

In plain text: Revit's Heating and Cooling Loads tool uses RTS and is hidden by default since Revit 2022. Systems Analysis runs EnergyPlus and adds sizing loads to analytical spaces. TRACE 3D Plus can send room loads and airflow back to Revit by gbXML. HVAKR doesn't need a space-bounded Revit model, and its free add-in round-trips MEP spaces between Revit and HVAKR.

Where HVAKR fits next to Revit

HVAKR doesn't need the Revit model to get started. It starts from the PDF or DXF sheets the architect already issues, which is often the fastest path when the architectural model isn't space-bounded or the MEP model lags the design. When you do have a model, the HVAKR add-in round-trips MEP spaces between Revit and HVAKR, so you don't re-key the model (see the next section).

1. Takeoff from sheets. Upload the drawing set. HVAKR reads sheet numbers, scales, ceiling heights, and levels where it's confident, and HVAKR AI proposes spaces you review level by level.[11][12]
2. Loads and outdoor air. RTS cooling across a design day in each month and steady-state heating, with ASHRAE 62.1 outdoor air by space type.[13]
3. Airflow, equipment, ducts. Air balancing per space, central and terminal unit configuration, and duct sizing against your duct-type criteria.
4. Back to Revit. The add-in round-trips MEP spaces between Revit and HVAKR. For design airflows, export the Ventilation and Airflow CSV or the Loads Report CSV and put the values on your Revit spaces. Team plans and up also export a gbXML model and raw JSON; the gbXML carries geometry, constructions, and inputs, not calculated loads or airflows.[14] Access to the HVAKR API is included with any paid HVAKR plan, with no add-on.

When architecture changes, update the sheet or the affected spaces, let HVAKR recalculate loads and airflows, and re-run duct sizing.

HVAKR's Revit add-in

• What it is. A free, open-source (Apache 2.0) add-in for Revit 2025 and 2026, distributed as an Autoloader bundle from the public repo github.com/flowcircuits/hvakr-revit-plugin. Revit loads it at startup and adds an HVAKR tab to the ribbon.
• What it does. It round-trips MEP spaces between your Revit model and HVAKR through HVAKR's API. It either creates a new HVAKR project or updates the one linked to the model, and it can list and read your HVAKR projects. You don't re-key the model.
• What you need. The add-in signs in with an HVAKR API key. Included with any paid HVAKR plan (Solo, Team, University, or Enterprise), with no add-on.
• What it doesn't do. It doesn't run loads inside Revit; loads are calculated in HVAKR. To put design airflows on your Revit spaces, use the CSV exports described above.
• How it differs from gbXML. HVAKR's gbXML export (Team plans and up) carries geometry, constructions, and inputs: weather design temperatures, schedules, per-space people, lighting, and equipment gains, and zone heating and cooling setpoints. It doesn't carry calculated loads or airflows.
• What HVAKR imports. Sheets come in as PDF or DXF only; DXF is converted to PDF on the server. There's no DWG or IFC import.

A workflow by design phase

• Schematic design. Revit Systems Analysis or a quick HVAKR model from the SD plans: block loads, equipment ballpark, envelope trade-offs.
• Design development. Run space-by-space loads and 62.1 outdoor air in your load tool of record. Assign zones and systems. Put design airflows on Revit spaces and size the terminal units.
• Construction documents. Re-run after the last architectural revision, export the load and ventilation reports for the submittal, and check the Revit space airflows still match the report.
• Every revision. Keep one source of truth for loads. If loads live in a load tool, treat the numbers in Revit as copies, and date them.

Before you export gbXML from Revit

• Every room you want analyzed has a space, and each space is enclosed and bounded top and bottom.
• Room-bounding is on for walls, floors, roofs, and ceilings that should bound spaces.
• Space names and numbers match the architectural room tags, so results map back.
• You exported with the space option your load program expects (TRACE 3D Plus asks for the Space export).[7]

FAQ

Can Revit do HVAC load calculations?

Yes, in two ways. The legacy Heating and Cooling Loads tool uses the ASHRAE Radiant Time Series method but is hidden by default since Revit 2022, and Systems Analysis runs EnergyPlus through OpenStudio workflows and adds sizing loads as properties on analytical spaces. Both need a clean, space-bounded model.

Why is Heating and Cooling Loads missing in Revit?

From Revit 2022 onward, Autodesk disables the Heating and Cooling Loads tool in the interface by default. Autodesk's support article says to add EnableHeatingAndCoolingLoads=1 under the Misc section of Revit.ini and reopen Revit.

What method does Revit use for HVAC loads?

Revit's Heating and Cooling Loads tool follows the ASHRAE Handbook of Fundamentals Radiant Time Series method. Revit Systems Analysis uses EnergyPlus, run through OpenStudio workflows, for HVAC system loads and sizing and for annual energy simulation.

Is Revit Systems Analysis good enough for final HVAC design?

It's useful for early design and energy studies, but its results depend on the energy analytical model, default schedules, and system definitions. Most mechanical engineers still document final loads and ASHRAE 62.1 outdoor air in a dedicated load program and treat Revit values as copies of that report.

How do I get HVAC loads back into Revit?

Either use a load program that exports results to Revit by gbXML (Trane TRACE 3D Plus can export room loads and airflow to Revit by gbXML), or enter design airflows on Revit spaces from your load report or CSV export. HVAKR's Revit add-in round-trips MEP spaces between Revit and HVAKR; for design airflows, use HVAKR's CSV exports.

Does HVAKR work with Revit?

Yes. HVAKR has a free add-in for Revit 2025 and 2026 that adds an HVAKR ribbon tab and round-trips MEP spaces between Revit and HVAKR, creating a new HVAKR project or updating a linked one, so you don't re-key the model. HVAKR doesn't need a Revit model to start, though: it works from PDF or DXF floor plans. HVAKR also exports CSV airflow data, and Team plans and up export a gbXML model.

Is there an HVAKR plugin for Revit?

Yes. The HVAKR add-in is a free download for Revit 2025 and 2026 from github.com/flowcircuits/hvakr-revit-plugin. It's open source (Apache 2.0), installs as an Autoloader bundle, adds an HVAKR tab to the Revit ribbon, and round-trips MEP spaces between the model and your HVAKR project through HVAKR's API. It signs in with an HVAKR API key, which is included with any paid HVAKR plan.

Does HVAKR's gbXML export include loads?

No. HVAKR's gbXML export carries geometry, constructions, and inputs: weather design temperatures, schedules, per-space people, lighting, and equipment gains, and zone heating and cooling setpoints. It doesn't include calculated loads or airflows, and it requires a Team plan or higher.

Sources (checked Oct 28, 2026)

• Autodesk Help (Revit 2027), "Heating and Cooling Reference" (RTS method): help.autodesk.com
• Autodesk Help (Revit 2027), "About the Heating and Cooling Loads Calculation" (analytical and inner volumes): help.autodesk.com
• Autodesk Support, "Missing Heating and Cooling Loads tool in Revit 2022 and later versions" (Oct 26, 2025): autodesk.com
• Autodesk Help (Revit 2025), "Run a Systems Analysis": help.autodesk.com
• Autodesk Revit Ideas forum, "Thermal load summary for radiant time series and heat balance methods" (Autodesk reply): forums.autodesk.com
• U.S. DOE, "Autodesk Brings Detailed EnergyPlus HVAC Simulation to Revit," Sept 30, 2019: energy.gov
• Trane, TRACE 3D Plus help, "gbXML Export" (version 7.0 and later): trace3dplus.help.trane.com; Trane TRACE page: trane.com
• Trane, "gbXML Export in TRACE 3D Plus" (Feb 21, 2025): shop.trane.com
• Trane, TRACE 700 FAQ, CDS-SLB021-EN (Mar 9, 2026): elibrary.tranetechnologies.com; Software support lifecycle: trane.com
• Elite Chvac (gbXML): elitesoft.com
• Ripple Engineering Software: rippleengineeringsoftware.com
• HVAKR Revit add-in (public repo): github.com/flowcircuits/hvakr-revit-plugin
• HVAKR docs: sheet library, AI space takeoff, load calculations, PDF export; API