What size compressor and vacuum do I need?
On this page
- Key facts
- Is there a FloorStack sizing calculator?
- How do you count vacuum users?
- What does a worked example look like?
- How do you size the compressor?
- What vacuum capacities are available?
- Should you size for future operatories?
- What should you give your dealer to confirm the sizing?
- How FloorStack helps
- Free tools for this step
- Frequently asked questions
- Sources
Size both by "users," not just chairs. Midmark counts each high-volume evacuator (HVE) in use at once as 1 user and each saliva ejector or nitrous scavenger as ½, then adds for piping and future rooms (Midmark). In 2026, pick a vacuum and compressor rated above that total and confirm with the manufacturer.
Key facts
| Item | Figure | Source |
|---|---|---|
| HVE | 1 user | Midmark |
| Saliva ejector | ½ user | Midmark |
| Nitrous scavenger | ½ user | Midmark |
| Chair air demand (A-dec 511) | 2.5 scfm minimum in normal use; 7.5 scfm peak | A-dec |
| Dry vacuum capacity (A-dec QuietCore+) | 5–12 users; 15–40 cfm at 8 inHg | A-dec |
| Compressor capacity (A-dec QuietCore+) | 3–12 users; 2.5–7.1 cfm at 80 psi | A-dec |
Is there a FloorStack sizing calculator?
It's coming soon. The free compressor & vacuum sizing calculator (coming soon) is planned to turn your chair count, devices and future rooms into a user count and size range. Until it launches, use the worksheet below, and always confirm sizing with your dealer and the manufacturer. Midmark itself notes its user counts are for planning purposes only (Midmark).
How do you count vacuum users?
Count the most devices running at the same time, not the total installed. Midmark's calculator asks for the maximum HVEs, saliva ejectors and nitrous scavengers in use at once, how many operatories use HVE for continuous evacuation, whether plumbing is overhead, the trunk line length, and how many operatories you plan to add. It notes piping length and configuration can add to the user count (Midmark).
Sizing worksheet
| Line | Your count | Multiplier | Users |
|---|---|---|---|
| HVEs in use at once | × 1 | ||
| Saliva ejectors in use at once | × ½ | ||
| Nitrous scavengers in use at once | × ½ | ||
| Future operatories (estimate their devices the same way) | |||
| Piping allowance (long or overhead runs; ask the manufacturer) | |||
| Total users |
Multipliers from Midmark.
To turn these ranges into a number for your own project, the free build-out cost & timeline calculator (coming soon) is planned to combine square footage, operatory count and region into a budget and schedule.
What does a worked example look like?
This is an illustration, not a recommendation. A four-operatory office might, at its busiest, run 4 HVEs, 2 saliva ejectors and 1 nitrous scavenger:
- 4 HVEs × 1 = 4 users
- 2 saliva ejectors × ½ = 1 user
- 1 nitrous scavenger × ½ = 0.5 user
- Total today: 5.5 users
Plan to add two operatories with similar use, and the total rises to roughly 8–9 users. Against A-dec's published QuietCore+ dry vacuum ratings, 5.5 users already exceeds the 5-user model; 8–9 users points to the 10-user model (A-dec). Your dealer may size differently for piping and workflow.
How do you size the compressor?
Compressors are rated by users and by airflow at pressure. A-dec's QuietCore+ compressor table runs from a 3-user model at 2.5 cfm at 80 psi to a 12-user model at 7.1 cfm (A-dec). Check your chairs' air demand too; A-dec's 511 chair guide calls for 80–125 psi at 2.5 scfm minimum in normal use (A-dec). Add air-driven lab equipment and any other air users. See choosing dental chairs.
| Model (A-dec QuietCore+) | Max users | Max cfm at 80 psi | Heat output (max BTU/hr) |
|---|---|---|---|
| SC3plus | 3 | 2.5 | 4,531 |
| SC5plus | 5 | 4.2 | 6,797 |
| SC7plus | 7 | 5.7 | 9,062 |
| SC10plus | 10 | 5.9 | 11,328 |
| SC12plus | 12 | 7.1 | 13,593 |
Source: A-dec compressor guide. Other brands rate differently.
What vacuum capacities are available?
| Model (A-dec QuietCore+ dry) | Max users | Vacuum at 8 inHg | Sound |
|---|---|---|---|
| DV5plus | 5 | 15 cfm | 64.8 dBA |
| DV7plus | 7 | 30 cfm | 70.9 dBA |
| DV10plus | 10 | 35 cfm | 71.0 dBA |
| DV12plus | 12 | 40 cfm | 76.2 dBA |
Source: A-dec vacuum guide.
Should you size for future operatories?
Usually yes. Midmark's calculator asks how many operatories you plan to add (Midmark), and an orthodontic designer lists mechanical rooms too small for growth among the most common mistakes (Practice Results / Ross Orthodontic). If you buy smaller now, leave floor space, power and piping for a second unit.
Bigger units make more heat and noise; plan the room around them. See dental mechanical room planning.
What should you give your dealer to confirm the sizing?
The sizing in this guide is a starting point. Before you order, send your dealer or installer the information they need to confirm the model:
| Information | Why it matters |
|---|---|
| Number of operatories, now and planned | Sets the number of vacuum and air users |
| Other users (sterilization, lab, hygiene) | Adds load beyond the chairs |
| Wet or dry vacuum preference | Changes the vacuum type and piping |
| Mechanical room location and size | Affects clearances, cooling and noise |
| Pipe run lengths to the farthest operatory | Affects pressure and flow at the chair |
| Equipment brands planned for each chair | Sets the air and vacuum demand per user |
Ask the dealer to put the final model, its rated capacity and the user count it was sized for in writing, and keep that note with your equipment inventory. If you add operatories later, send the same table again with the new counts so the dealer can check whether the existing units still have enough capacity.
How FloorStack helps
FloorStack is a dental build-out platform that keeps chair counts, devices and future rooms on one plan, so mechanical sizing reflects the real office. Start at the Dental Equipment Planning hub, and see the startup equipment budget and dental office equipment list.
Related guides: wet vs. dry vacuum and running dental vacuum lines.
Free tools on the FloorStack dental build-out platform for this step: Build-out cost & timeline calculator (free tool, coming soon) and Compressor & vacuum sizing calculator (free tool, coming soon).
Free tools for this step
- Build-out cost & timeline calculator (free tool, coming soon): estimate budget and schedule from your square footage, operatory count and region.
- Compressor & vacuum sizing calculator (free tool, coming soon): size the compressor and vacuum to your chair count; confirm with your dealer.
Frequently asked questions
How do I calculate dental vacuum size?
Count devices used at the same time: each HVE is one user, each saliva ejector and nitrous scavenger is half. Add for piping and future rooms, then confirm with the manufacturer.
How many users does a 4-operatory office need?
It depends on simultaneous use. One illustrative 4-op scenario totals 5.5 users today and about 8–9 with two future rooms.
How much air does a dental chair use?
A-dec's 511 chair guide calls for at least 2.5 scfm at 80–125 psi in normal use, with 7.5 scfm peak.
Should I oversize my dental vacuum?
Size for planned growth. Replacing an undersized vacuum later costs more than buying the right capacity now.
Is there a free dental compressor and vacuum sizing calculator?
FloorStack's calculator is coming soon. Midmark also publishes a user count calculator for planning.
Do compressors and vacuums produce heat?
Yes. A-dec lists maximum heat output of 4,531–13,593 BTU/hr for its compressors, depending on model.
Sources
More in Dental Equipment Planning
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