Allegro 9533-25 Confined Space Blower — 8 in Axial AC, 831 CFM Free Air, 25 ft Duct

Allegro 9533-25 Confined Space Blower overview

The Allegro 9533-25 Confined Space Blower is an 8-inch axial AC ventilation unit built to move air into or out of manholes, tanks, vaults, and sewers. It ships as a complete kit — the 1/3 HP blower, 25 ft of 8-inch ducting, a quick coupler, and a compact storage canister — in a lightweight polyethylene housing that shrugs off corrosion, UV, and many chemicals. Because the coupler attaches on either side, the same unit works as a supply blower or an exhauster. Ventilation is a core part of confined-space work, and it pairs directly with atmospheric monitoring — see our best personal gas detector guide and the 4-gas vs single-gas breakdown.

Two numbers matter, and both are easy to misread. First, airflow: 831 CFM is a free-air rating measured at the outlet with no duct attached. In the real world, duct length and bends cut that down — Allegro lists roughly 709 CFM at one 90-degree bend and about 586 CFM at two — so plan around the ducted figure. Second, the atmosphere it's rated for: this is a standard AC blower, not explosion-proof. If a space may hold flammable or explosive gas, you need an explosion-proof or air-driven blower instead. And ventilation, however good, does not make air safe on its own — you still test before and during entry, and for low-oxygen or immediately hazardous work you need supplied air, covered in when do you need a respirator, best respirator by industry, and the respiratory protection guide.

Where the blower fits

It's built for routine confined-space ventilation — purging a manhole before entry, keeping fresh air moving during work, or exhausting fumes from a tank or vessel. It suits utilities, municipalities, and industrial maintenance crews that need portable, non-hazardous-atmosphere ventilation. Where it is not the right tool is a confirmed flammable or explosive atmosphere (use an explosion-proof or pneumatic blower) or as a substitute for breathing air — for low-oxygen or immediately dangerous entry you need an Allegro supplied-air respirator system or the appropriate supplied-air setup, with a powered Allegro EZ Air PAPR for lighter hazards. Keep atmospheric monitoring from the gas-detector lineup on hand, and review the gas detector guide to match the meter to the space.

Pros & cons

Airflow with ducting

Airflow is the number that drives a ventilation plan, and it falls as you add duct length and bends — size the run so the delivered flow still turns the space's air over often enough, then confirm the result with monitoring per the 4-gas vs single-gas guidance.

Specifications

Related guides

• Best personal gas detector
• When do you need a respirator?
• Best respirator by industry
• Best PAPR respirator systems

Related resources

• Forensics Detectors 4-gas confined-space meter
• Allegro EZ Air PAPR blower
• OSHA 1910.134 respiratory protection standard
• Shop gas detectors
• Shop respiratory protection

Frequently asked questions

What's included in the Allegro 9533-25 blower kit?

The kit includes the 8-inch axial AC blower, 25 ft of 8-inch ducting, a quick coupler, and a compact storage canister. Allegro also offers the same blower with 15 ft or 50 ft of duct, or as a blower only.

Is 831 CFM the airflow at the end of the duct?

No. The 831 CFM figure is a free-air rating measured at the blower outlet with no ducting. Real airflow drops once you attach duct and route it around corners — Allegro lists roughly 709 CFM with one 90-degree bend and about 586 CFM with two. Plan your ventilation around the ducted number, not the free-air number.

Can the 9533-25 both blow air in and exhaust air out?

Yes. The coupler and duct can attach to either side, so the unit works as a supply blower to push fresh air into a space or as an exhauster to pull contaminated air out. Choose the mode that fits your ventilation plan.

Is the blower explosion-proof or safe for flammable atmospheres?

No. This is a standard AC-powered blower and is not explosion-proof or intrinsically safe. If the atmosphere may contain flammable or explosive gas or vapor, use an explosion-proof or air-driven (pneumatic) blower rated for that hazard instead.

Does ventilating a space make it safe to enter?

No. Ventilation helps control the atmosphere, but it does not guarantee safe air. You still test the atmosphere with a calibrated gas detector before and continuously during entry, and follow your permit-required confined-space program.

What power does it need?

It runs on 115–230V AC, 50/60 Hz, with a 1/3 HP motor spinning around 3,400 rpm. Use a properly rated circuit and cord, and keep the electrical connections out of wet or hazardous areas.

What size is the duct, and are other lengths available?

This kit ships with 8-inch diameter ducting 25 ft long. Allegro offers 15 ft and 50 ft versions of the same blower; longer duct and more bends reduce delivered airflow, so size the run to the job.

What confined spaces is it designed for?

Vertical and horizontal confined spaces such as manholes, storage tanks, vaults, sewers, and vessels, where you need to move fresh air in or pull stale or contaminated air out through the opening.

How do I set it up to blow versus exhaust?

Attach the duct to the intended side of the blower: outlet side to push air into the space (supply), or inlet side to draw air out (exhaust). Position the duct end where it will move air through the work zone, not just at the opening.

Do I still need a gas detector with the blower?

Yes. Atmospheric testing is mandatory for permit-required confined-space entry. The blower manages airflow; a calibrated multi-gas detector confirms oxygen level and the absence of toxic or flammable gas before and during the work.

What is the housing made of, and is it weather-resistant?

The housing and canister are polyethylene, which keeps the unit lightweight and resistant to corrosion, UV, and many chemicals. Still store it dry and protect the motor and cord from water.

What's the difference between the 9533-25 and the 15 ft or 50 ft versions?

The blower is the same; the number after the dash is the duct length. The 9533-15 ships with 15 ft of duct and the 50 ft version with 50 ft. More duct and more bends lower delivered airflow, so match the length to how far you need to reach.

Reviewed by Steven Eaton, WC Safety. Specifications reflect Allegro's published data and can vary; confirm airflow, duct length, and hazard suitability for your specific unit, and follow your written confined-space program before use.