Two measurements describe different work
Airflow and sealed pressure are related but not interchangeable. Airflow, usually published in cubic feet per minute (CFM), describes how much air the vacuum can move. Sealed pressure—often stated as inches of water lift—describes how strongly the vacuum can pull when airflow is restricted. A useful comparison considers both, along with the hose, filter and tool attached to the machine.
When airflow matters most
Higher airflow helps carry light, bulky debris through the hose: sawdust, wood chips, dry leaves and general floor mess. It also matters when a vacuum is attached to a tool that creates a continuing stream of dust. Published CFM is commonly measured at a particular point and without every real-world restriction, so do not assume the full number reaches the nozzle after adding a long hose, fine filter and small port.
When sealed pressure matters most
Stronger sealed suction helps when lifting denser material, pulling water, using a narrow nozzle or overcoming resistance through a restricted path. A machine with excellent water lift but modest airflow may feel strong at a crevice tool yet move large volumes of light debris less quickly than another model. Compare like units, because manufacturers may publish sealed pressure in inches, millibars or kilopascals.
Hose diameter changes the behavior
A large hose is less likely to clog on chips and can support high-volume cleanup. A smaller hose is easier to handle and may increase air velocity at the pickup point, but it restricts total flow and clogs more readily on large debris. Tool ports, reducers, elbows and long corrugated hoses add resistance. Match the hose to the debris and the machine instead of treating diameter as a quality score.
Filters change usable performance
A clean coarse filter creates less resistance than a loaded fine-dust filter. As dust accumulates, airflow normally falls. Automatic filter cleaning, easy manual cleaning or a pre-separator can help maintain performance during dusty work. When comparing numbers, also compare the required filtration setup—running without the correct filter is not a fair or safe way to gain airflow.
What the headline “horsepower” means
Many wet/dry vacuums advertise peak horsepower. That is not the same as the continuous mechanical output you would compare on an industrial motor. For practical shopping, CFM, sealed pressure, electrical rating, hose size, noise, capacity and filtration provide more useful context than peak horsepower alone.
Comparison checklist
- Use CFM as an airflow indicator for high-volume debris and dust collection.
- Use sealed pressure as a suction indicator for restricted pickup and liquids.
- Check where and how each value was measured.
- Match hose diameter to the debris and tool ports.
- Compare performance with the filtration you actually need.
Sources and further reading
- Shop-Vac product and operating FAQs
- RIDGID wet/dry vacuum support
- NIOSH: control of wood dust from woodworking machinery
Published test methods vary. Treat CFM and sealed pressure as comparison inputs, then account for the filter, hose, accessories and debris in your real setup.