Guide · Nov 5, 2026
How to Read HVAC and Mechanical Plans: Duct Layouts, Equipment Schedules and Notes
By Eli Gewirtzman, Owner · Last checked Nov 5, 2026
An HVAC (mechanical) plan is the floor plan with the walls drawn light and the heating, cooling and ventilation system drawn on top. Start with the legend and notes, find the equipment (furnace, air handler, condenser, heat pump), then trace the supply ducts out to each register and the return ducts back. Every duct carries a size, every register carries an airflow in CFM, and every tagged piece of equipment is listed in the equipment schedule.
Mechanical sheets usually carry an M prefix, like M-101. Our guide to what sheet numbers like A-101 mean covers the numbering. On a small house, the HVAC layout may be a single sheet, or the duct layout may come from the HVAC contractor rather than the designer, so check the sheet index first.
1. Start with the legend and the mechanical notes
Mechanical sheets lean on symbols and line types, so read the legend before anything else. Most offices show:
- Supply ducts and registers: often drawn with a square or rectangle and an X, or labeled S or SA.
- Return ducts and grilles: often a diagonal line in one direction, or labeled R or RA.
- Exhaust: bath fans, kitchen hoods and dryer vents, labeled EF or EA.
- Thermostats: usually a small circle with a T.
The general notes then set duct materials, insulation, sealing and code references. Louisville, Colorado’s residential checklist, for example, asks designers to note on the plans that “all mechanical installations shall comply with” the adopted mechanical code, and it lists items like dryer venting and kitchen exhaust that end up as notes on the mechanical sheet. Read the notes on the sheet you’re working from; they apply to everything drawn on it. Our blueprint abbreviations guide decodes the shorthand.
2. Read the duct layout
The duct layout is the heart of the mechanical plan. Hanover County, Virginia, describes what it wants on a residential submittal: a “duct system layout, including duct sizes, diffuser sizes/flow rates, and equipment locations,” and it says the layout “shall be superimposed over the floorplan for the floor served.” That is exactly how to read one:
- Find the equipment. The furnace or air handler is the starting point. The outdoor condenser or heat pump is usually outside the walls with refrigerant lines running in.
- Follow the trunk. The main supply duct, or trunk, leaves the equipment with the largest size, like 16×8 (width by height, in inches) or 12″ round.
- Follow each branch. Smaller branch ducts, often 6″ or 8″ round, split off the trunk to each room.
- Read each register. At the end of each branch is a register with a size and an airflow number in CFM (cubic feet per minute), like 6″ / 85 CFM.
- Trace the returns. Return grilles pull air back to the equipment. On many houses there are only one or two large central returns.
If you’ve read our floor plan guide, the room names and walls will be familiar. The mechanical sheet adds the air.
3. Read the equipment schedule
The equipment schedule is a table listing each tagged unit. A tag like AHU-1, F-1, CU-1 or HP-1 on the plan points to a row in the schedule.
| Column | What it tells you |
|---|---|
| Tag | Matches the label on the plan (AHU-1, CU-1, EF-1) |
| Type / description | Furnace, air handler, heat pump, condenser, mini split, exhaust fan |
| Capacity | Heating output in BTU/h, cooling in tons or BTU/h |
| Airflow (CFM) | How much air the fan moves |
| Efficiency | Ratings such as AFUE for furnaces or SEER2 for cooling |
| Electrical | Voltage and circuit data the electrician needs |
| Manufacturer / model | Basis of design; the installer may submit an equal |
Hanover County asks for “manufacturer’s specifications for mechanical equipment to be used,” which is why the schedule and the cut sheets have to agree. If a tag on the plan isn’t in the schedule, or the CFM on the schedule doesn’t match the total of the registers it serves, ask the designer or HVAC contractor before equipment is ordered. The electrical data in the schedule also ties to the panel schedule; our electrical blueprints guide shows where that ends up.
4. Understand Manual J, S and D
Many building departments ask for HVAC design calculations along with the drawings. The three you’ll hear about are ACCA manuals:
| Manual | What it does | What you’ll see in the set |
|---|---|---|
| Manual J | Calculates how much heating and cooling each room needs | A load report with room-by-room BTU/h |
| Manual S | Selects equipment that matches that load | The equipment schedule and cut sheets |
| Manual D | Sizes the ducts to deliver the right CFM to each room | The duct layout with sizes and CFM |
Hanover County requires summary information from the load calculation software, including “design inputs and calculated outputs,” and says only ACCA-approved software may be used. Bingham County, Idaho, lists a residential mechanical drawing set as “Manual J, S, D” plus a “Mechanical Layout,” and for new homes it asks for heat load calcs and duct design “provided from the mechanical contractor.” Louisville, Colorado, lists “Mechanical Plans, Manual J, D and S” among the documents a new home must have with no deferred submittals.
When reading, the useful check is simple: the room CFM numbers on the duct layout should come from the Manual J/D report, and the equipment in the schedule should come from Manual S.
5. Check ventilation, exhaust and combustion air
Modern houses are tight, so mechanical plans also show how fresh air gets in and stale air gets out. Look for:
- Whole-house ventilation: an ERV, HRV, or a fan with a timer, often with its own tag and CFM.
- Bath and kitchen exhaust: fan tags with CFM and duct runs to the exterior.
- Dryer vent: Louisville’s checklist cites a maximum length for a 4″ dryer duct with two elbows, so expect the route to be shown.
- Combustion air: for gas furnaces and water heaters, Louisville asks designers to “show combustion air for all fuel-burning appliances.”
What permit reviewers look for on mechanical sheets
| Item | Hanover County, VA | Bingham County, ID | Louisville, CO |
|---|---|---|---|
| Duct layout | Over the floor plan, with duct and diffuser sizes, flow rates, equipment locations | “Mechanical Layout” | Mechanical plans required |
| Load calcs (Manual J) | Summary of inputs and outputs, ACCA-approved software | Required | Required |
| Equipment selection (Manual S) | Required, with manufacturer’s specs | Required | Required |
| Duct design (Manual D) | Required | Required | Required |
| Combustion air shown | Not stated | Not stated | Yes |
| Printed sheet size | No larger than 11×17 if printed | Not stated | Not stated |
Your town’s list may differ. For how many paper copies a building department wants, see our plan copy requirements by state.
Printing mechanical sheets
Duct layouts are dense: every branch has a size and every register has a CFM, so print them at the size they were drawn at. A half-size print halves every label. Most residential sets are drawn on 24×36. If the designer color-coded supply and return, print those sheets in color so the legend still works; otherwise black and white reads fine. One exception: some departments set a maximum size for printed mechanical sheets, as Hanover County does at 11×17, so check before you print a permit copy.
PrintMyPlans.com prints PDF plans on 20 lb bond at $1.95 per sheet in black and white or $3.75 in color, the same price at every size: 17×22, 18×24, 22×34, 24×36, 30×42 and 36×48. Printing only, before shipping:
| Example | Sheets | Black & white | Color |
|---|---|---|---|
| Duct layout and equipment schedule, 1 copy | 2 | $3.90 | $7.50 |
| 3-sheet mechanical set, 1 copy | 3 | $5.85 | $11.25 |
| 3-sheet mechanical set, 2 copies (HVAC contractor and site) | 6 | $11.70 | $22.50 |
WELCOME20 takes 20% off a first order, so the 6-sheet color example comes to $18.00 in printing. Price your own set with the plan printing cost calculator. For trade and field sets, see construction plan printing, and for complete house sets, architectural plan printing.
We print plans; we don’t design, stamp, check or change them. Questions about duct sizes, equipment or code items go to your designer or HVAC contractor.
FAQ
What is the difference between a mechanical plan and an HVAC plan?
On houses they’re usually the same thing. “Mechanical” is the discipline name (M sheets); HVAC is the system most of those sheets show.
What does CFM mean on HVAC plans?
Cubic feet per minute, the amount of air a register, grille or fan moves. Each room’s CFM comes from the load and duct design.
How do I tell supply from return ducts?
Use the legend. Supply and return are drawn with different symbols, labels or colors, and returns usually run back to the air handler from one or two large grilles.
What is a Manual J?
An ACCA load calculation that figures heating and cooling needs room by room. Many building departments ask for it with the mechanical plans.
Should HVAC plans be printed in color?
Only if the legend uses color for supply, return or exhaust. Otherwise black and white works.
For other sheets in the set, see our guides to structural drawings, plumbing plans, types of construction drawings and how to read blueprints.
Printing it
When the PDF is final, upload it on the order page and choose the size it was drawn at, black and white or color, and the number of copies. Order by 3 PM ET on business days and it ships same day, arrives as soon as the next day, rolled in protective tubes, to all 50 states. Free 2-day air shipping on orders over $95 (lower 48 states).
Sources
- Hanover County, VA, Building Inspections, residential HVAC submittal requirements (Manual J/S/D, duct layout)
- Bingham County, ID, Planning and Development, Residential Permit Application Checklist (July 2024)
- City of Louisville, CO, 2024 IRC/IECC Residential Plan Review Checklist (revised 11/20/2025)
Order by 3 PM ET, ships same day. Delivery timing depends on the shipping service and destination. See the terms for business-day and holiday details.