Types of Autoclaves: A Buying Guide for Lab, Clinical and Industrial Procurement

An autoclave is a pressure vessel that uses saturated steam under pressure to sterilize equipment, media, and waste. “Types of autoclaves” is really three separate classification questions layered on top of each other — how the unit is loaded and sized, how it removes air and validates a sterilizing cycle, and what application or regulatory setting it’s built for — and a procurement decision has to answer all three before a chamber-size or price comparison means anything. This guide walks through each classification, how they map onto real buying criteria, and where to go for depth on sizing, cost, and installation once you know which type you need.

Autoclave vs. Sterilizer: Are They the Same Thing?

In practice, most labs use “autoclave” and “steam sterilizer” interchangeably, and for procurement purposes that’s usually fine — but the terms aren’t identical. Sterilizer is the broader category: any device that achieves sterility, which also includes non-steam technologies such as dry-heat ovens, ethylene oxide (EtO) chambers, vaporized hydrogen peroxide systems, and low-temperature gas plasma units, all of which are regulated as medical devices in the US when marketed for healthcare use. Autoclave refers specifically to a steam-under-pressure sterilizer. Every autoclave is a sterilizer; not every sterilizer is an autoclave. The distinction matters at the procurement stage mainly when you’re comparing quotes or specification sheets across vendors — if a “sterilizer” quote turns out to be an EtO or dry-heat unit rather than a steam autoclave, it will have a completely different footprint, cycle time, consumables cost, and ventilation requirement than what you budgeted for.

Types of Autoclaves by Loading Configuration

The most visible distinction when comparing equipment is physical: how the unit loads and how much floor space it needs.

• Benchtop (tabletop) autoclaves. Small-chamber units (commonly under 25 liters) designed to sit on a countertop. The standard choice for research labs, dental offices, small clinics, and tattoo/veterinary settings with modest, frequent-cycle throughput needs.
• Vertical autoclaves. Floor-standing units with a top-loading chamber, often used where floor footprint is limited but somewhat higher capacity than benchtop is needed.
• Horizontal autoclaves. Front-loading, larger-capacity units, common in hospital sterile processing and industrial settings where carts or trays are wheeled directly into the chamber.
• Pass-through (double-door) autoclaves. Two doors on opposite chamber walls, with a bioseal between them, so the unit physically separates a “dirty” loading side from a “clean” unloading side. Standard in hospital CSSDs and required in higher-containment biosafety facilities to prevent contaminated and sterilized items from crossing paths.

Loading configuration is the first filter in a purchase decision because it’s constrained by your facility, not just your workload — available floor space, doorway/hallway clearance for delivery, plumbing and electrical service location, and (for pass-through units) whether you actually have two separate rooms to install between.

Types of Autoclaves by Sterilization Class and Cycle

The second classification is about validated capability, not size. Small steam sterilizers sold in Europe and many other markets are classified under EN 13060 by the load types they’re proven to sterilize:

• Class N — unwrapped, solid, non-porous loads only (e.g., solid instruments, glassware). No fractionated vacuum phase.
• Class S — a defined, manufacturer-specified range of load types between N and B (may include some wrapped or hollow items, per that model’s validation documentation).
• Class B — full fractionated-vacuum cycle, validated for wrapped, porous, and hollow-lumen loads. This is the class most labs and clinical settings actually need if they process anything other than solid unwrapped items, and it’s the class that requires routine Bowie-Dick testing.

That class distinction is driven by cycle type: a gravity displacement autoclave removes air by letting incoming steam push denser air out through a bottom drain (mechanically simple, adequate only for solid unwrapped loads), while a pre-vacuum (dynamic-air-removal) autoclave uses a vacuum pump to actively evacuate air before introducing steam, giving it the penetration needed for wrapped and hollow loads — the underlying mechanism behind EN 13060 Class B. A third method, steam-flush pressure-pulse (SFPP), achieves similar air removal through repeated steam flushes and pressure pulses without a vacuum pump. For the full mechanics of each cycle and how to match one to a specific load (glassware, wrapped instrument packs, media, liquids in vented containers), see How to Operate a Lab Autoclave: Cycle Types Explained.

In the US, the comparable reference points are ANSI/AAMI ST55 (table-top steam sterilizers) and ANSI/AAMI ST79 (comprehensive guidance for steam sterilization in healthcare facilities); large industrial and pharmaceutical sterilizers are more commonly validated against ISO 17665 (moist-heat sterilization of health care products) or, for hospital-scale units, EN 285.

Types of Autoclaves by Application

The third layer is setting, which usually determines both the class you need and the documentation a vendor has to be able to provide:

• Laboratory / research autoclaves. Used for media preparation, glassware, and biohazardous waste decontamination. A gravity-cycle benchtop unit is often sufficient unless the lab also processes wrapped instrument packs or requires a validated biological-waste kill cycle.
• Medical and dental instrument sterilizers. Typically require Class B (EN 13060) or equivalent ANSI/AAMI ST55/ST79-conformant capability, because reusable instruments are wrapped or have lumens.
• Hospital sterile processing department (CSSD) sterilizers. Large-capacity, usually horizontal or pass-through units built to hospital-scale throughput, governed by ANSI/AAMI ST79 in the US. See Sterile Processing Department (CSSD) Equipment Purchasing for the full procurement framework at that scale.
• Pharmaceutical and industrial autoclaves. Large, often custom-configured vessels used for terminal sterilization of manufactured products, validated under ISO 17665 with a full installation/operational/performance qualification (IQ/OQ/PQ) package — see CASRAI’s IQ/OQ/PQ entry for what that documentation actually covers.

Autoclave Sizes: Matching Capacity to Type

Chamber capacity (quoted in liters or cubic feet) and loading configuration are related but not the same decision — a small facility can still need a horizontal unit if it processes bulky trays, and a large lab can run several benchtop units instead of one big chamber if throughput is spread across shifts or rooms. Undersizing forces more cycles and slower turnaround; oversizing wastes utility costs and floor space, and can even under-load cycles in a way that affects validation. For the sizing methodology — matching chamber volume to actual load volume, cycle frequency, and growth headroom — see How to Size an Autoclave Chamber: A Buying-Guide Framework.

How Much Does Each Type Cost?

Cost tracks the classifications above closely: a Class B unit generally costs more than an equivalent-size Class N unit because it needs a vacuum pump and more sophisticated cycle control; pass-through and hospital-scale horizontal units cost substantially more than benchtop units; and units sold with a full IQ/OQ/PQ documentation and calibration-certificate package cost more than identical hardware sold without it — but that documentation is frequently what a lab or hospital actually needs to pass an accreditation inspection. Purchase price is also only part of the real cost of owning an autoclave once you factor in installation, consumables, service contracts, and validation testing. For order-of-magnitude price bands across lab, industrial, and hospital settings, see How Much Does an Autoclave Cost?; for the full lifetime-cost comparison, see Autoclave Total Cost of Ownership and Autoclave Lease vs. Buy.

How to Choose an Autoclave: A Procurement Checklist

Once you understand the classification landscape, narrowing to a specific purchase comes down to a defined set of questions:

• What load types will you actually run? Solid/unwrapped only points to Class N; anything wrapped, porous, or with a lumen requires Class B (or documented Class S coverage for that specific load).
• What standard or accreditation requirement applies to your setting? A clinical or hospital purchase should be evaluated against ANSI/AAMI ST55/ST79 (US) or EN 13060/285 (EU and many other markets); an industrial or pharmaceutical purchase against ISO 17665.
• Can the vendor supply full documentation? Ask for IQ/OQ/PQ protocols, calibration certificates, and (where applicable) FDA premarket clearance documentation before you buy, not after — retrofitting validation onto equipment that wasn’t sold with it is expensive and sometimes not possible.
• Does your facility meet the installation requirements? Water supply, drainage, electrical service (or house steam), and floor loading all vary significantly between a benchtop unit and a floor-standing or pass-through model — confirm this before finalizing chamber size or configuration. See Autoclave Installation Requirements.
• What does the total cost of ownership actually look like? Service contract terms, consumables (chemical/biological indicators, printer paper, filters), and expected downtime should factor into the comparison alongside purchase price — and whether leasing makes more sense than buying for your budget cycle.
• How will you source and support the unit? Options typically include buying direct from the manufacturer, through a group purchasing organization (GPO) contract, or through a medical/laboratory supply distributor — for example, lac.us lists autoclaves and sterilization consumables alongside other lab and medical supply categories. Whichever channel you use, confirm the same things: documented service/support coverage, availability of validated replacement parts, and a real warranty, not just the lowest quoted price.

Once a unit is installed, ongoing performance depends on routine biological and chemical indicator testing (see Autoclave Validation), a documented maintenance program (see Biomedical Equipment Maintenance), and a plan for the failure modes specific to your cycle type (see Autoclave Troubleshooting and Autoclave Operating Safety).

Frequently Asked Questions

What’s the difference between an autoclave and a sterilizer?

“Sterilizer” is the broader category and includes non-steam technologies (dry heat, EtO, hydrogen peroxide gas plasma); “autoclave” specifically means a steam-under-pressure sterilizer. Every autoclave is a sterilizer, but not every sterilizer is an autoclave.

How much does an autoclave cost?

Price depends on chamber size, sterilization class (Class B costs more than Class N), construction, and whether a validation/documentation package is included. See How Much Does an Autoclave Cost? for order-of-magnitude price bands by setting.

What autoclave sizes are available?

Benchtop units commonly run under 25 liters; floor-standing and hospital-scale horizontal or pass-through units can run into the hundreds of liters. The right size depends on load volume and cycle frequency — see How to Size an Autoclave Chamber.

How do I choose the right type of autoclave for my lab?

Start from the load types you’ll actually run (which determines the sterilization class you need), then confirm the applicable standard for your setting, verify the vendor can supply full validation documentation, and check that your facility meets the unit’s installation requirements before comparing price.

Is a gravity displacement autoclave good enough for my lab?

Only if you exclusively process solid, unwrapped, non-porous loads. Anything wrapped, porous, or with a lumen (instrument packs, tubing, some bottled liquids) needs a pre-vacuum (Class B) cycle to reliably reach sterilizing conditions throughout the load.