# How is a hospital medical vacuum plant sized?

**What inputs determine the size of a hospital medical vacuum plant?**

Under the NHS England guidance HTM 02-01 (2026), a hospital medical vacuum plant is sized from the diversified design flow of the areas it serves, using a design flow per terminal unit and a diversity formula per department; the pumps should still supply that flow during maintenance on any pump plus a further single fault.

## Step 1: define the rooms

At design stage the project team defines the requirements of each room or space. HTM 02-01 (2026) notes that pipeline flow cannot be predicted precisely, so it gives guideline values that have proved adequate in practice. In general note II of its annex, Portugal's ACSS ET 03/2006 asks designers to confirm the number of outlets and the real utilisation coefficients, and to apply one of FD S 90-155, HTM 2022, AS 2896-1998 or SIS HB 370 when sizing the distribution; HTM 2022 has since been superseded by HTM 02-01 (2026), and section 16 of the same specification lists AS 2896-2011.

## Step 2: apply design flows and diversity

HTM 02-01 gives, for each department, a design flow per terminal unit and a formula for the diversified flow Q. Medical vacuum is typically 40 L/min per terminal unit; each operating room needs 80 L/min because the surgical team and the anaesthetist may use suction together. In the formulas, n is the number of beds, treatment spaces or single rooms where the procedure is performed, not the number of terminal units.

| Area (HTM 02-01, Table 10) | Design flow per terminal unit | Diversified flow Q |
|---|---|---|
| Emergency department, resuscitation room (per trolley space) | 40 L/min | Q = 40 + [(n − 1)10] |
| Operating room | 80 L/min per room (40 L/min per terminal unit) | Q = 80 |
| Critical care areas | 40 L/min | Q = 40 + [(n − 1)10] |

For a 28-bed ward unit with single rooms, four-bed rooms and a treatment room, the diversified flow is based on 40 L/min. The pipework is then designed on the diversified flows and the permissible pressure loss.

## Step 3: choose the pumps and the vessel

- Capacity should match the calculated demand (10.5). Pump capacity is stated as free air aspirated in L/min, with the pump at 475 mmHg (63 kPa) and at 450 mmHg (60 kPa) at the plant pipeline connection (10.27).
- The pumps are arranged so that, during maintenance on any pump and a further single fault, the remaining pumps still supply the system design flow (10.17). See [how many pumps a plant needs](https://library.ultracontrolo.com/answers/how-many-vacuum-pumps-does-a-hospital-need/).
- The vessel is sized to minimise stop/start cycles, which should stay within the manufacturer's recommendation, typically six per hour (10.19), and the Table 20 note sizes the reservoir's water capacity at a minimum of the total design flow rate. ACSS sets a maximum of 20 starts per hour for each pump.

## ULTRAVAC

ULTRAVAC plants are configured with 1 to 12 pumps of 3 to 1,600 m³/h each and vacuum vessels of 24 to 6,000 litres, so the number of pumps and the vessel size can follow the calculated design flow.

### Does a day unit use the same demand basis as a 24-hour hospital?

No. HTM 02-01 (2026) says sites that are not open 24/7 should consider demand across their working hours only.

### Is dental suction sized the same way?

No. HTM 02-01 bases dental high volume systems on 300 L/min at each chair cannula connector, with their own diversity rule.

## Sources

- [NHS England, HTM 02-01 Medical gas pipeline systems, Part A (2026 edition), paras 4.43 to 4.47, 4.109, 4.117, 10.5, 10.17, 10.19, 10.27, 11.39 and Tables 10 and 20; Context (supersedes HTM 2022)](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-a-design-installation-validation-verification-aug-2026.pdf)
- [ACSS, ET 03/2006 v.2024, Especificações técnicas para gases medicinais e aspiração em edifícios hospitalares, sections 4.8 and 16 and annex note II](https://www.acss.min-saude.pt/wp-content/uploads/2016/10/ET-03_2006_v2024-Gases-medicinais_VF.pdf)
- [ULTRAVAC datasheet, pp. 2, 3 and 5](https://www.ultracontrolo.com/products/ultravac)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/how-is-a-medical-vacuum-plant-sized/