By the SightShield team · · 3 min read
Three numbers on every datasheet
| Rating | What it measures | Why it matters |
|---|---|---|
| Airflow (CFM) | Volume of air moved per minute | Carries dust and debris through the hose and pipes |
| Water lift (inches) | Maximum sealed suction | Pulls dirt out of carpets and keeps suction over long pipe runs |
| Air watts | A combined measure of airflow and suction | The single best number for comparing units |
An example
Beam (now part of Canada’s Trovac Industries) lists its 650 air-watt residential units at 142 CFM airflow and 116 inches of water lift, rated for homes up to about 8,000 sq ft. Other brands publish similar figures — for instance, Broan-NuTone lists a 650 air-watt unit at 130 inches of water lift for homes up to 9,000 sq ft. These are manufacturers’ ratings; always use the sizing table for the specific model.
Typical sizing
| Home | Typical power unit | Notes |
|---|---|---|
| Duplex flat, 1,500–2,500 sq ft | Around 450–550 air watts | Short pipe runs |
| Independent house, 2,500–3,500 sq ft | Around 550–650 air watts | Most common size |
| Large villa, 5,000+ sq ft | 700+ air watts | Long runs, several floors |
| Very large or multi-building | Larger unit or two units | Split by zone |
What pushes you to a bigger unit
- Long pipe runs from the power unit to the farthest inlet.
- Many inlets and bends.
- Several floors, especially if the unit is in the basement and inlets are two or three floors up.
- Lots of carpets and rugs, which need more suction.
- Plans to use the system for cars or the garage.
Pipe layout matters as much as the motor
- Keep the trunk line as short and direct as practical between the power unit and the farthest inlet.
- Use sweep fittings designed for central vacuums, not plumbing elbows, to avoid clogs.
- Minimise the number of bends in each branch.
- Install the pipe with the correct orientation of fittings so debris flows towards the unit.
- Seal all joints; air leaks reduce suction at every inlet.
Where to put the power unit
Typical locations are a utility room, basement, garage, staircase cupboard or service area. The space needs ventilation for the motor to stay cool, a dedicated power point, easy access for emptying and maintenance, and a short route to an outside wall for the exhaust. Avoid bedrooms and study areas, because the unit itself is noisy, and avoid wet bathrooms.
Do not oversize blindly
A bigger motor uses more power and makes more noise at the unit, and it cannot make up for a badly designed pipe network. Good layout — short runs, sweep fittings, sensible inlet placement — matters as much as the motor. The installer should calculate the longest run and choose a unit with headroom, not simply the biggest one available.
Central vacuum installation →Electrical supply
Residential central vacuum units draw significant current when running. Provide a dedicated circuit with an appropriate breaker as specified by the manufacturer, and plan the low-voltage control wire that runs from each inlet to the unit. Your electrician should include both in the electrical drawings.
Quick answers
How many air watts do I need for a central vacuum?+
Around 550–650 air watts suits most 2,500–3,500 sq ft houses. Large villas often need 700 or more. Check the manufacturer’s sizing table.
What is water lift in a central vacuum?+
Water lift is the maximum sealed suction, measured in inches of water. Higher water lift helps on carpets and over long pipe runs.
Is CFM or water lift more important?+
Both matter, which is why air watts — combining the two — is the best single number for comparing units.
Can one power unit serve a G+2 villa?+
Usually yes, if the unit is sized for the pipe length and inlet count, and the pipe layout is efficient.
Does a bigger power unit use much more electricity?+
Larger motors draw more power while running, but vacuuming time is short, so the difference in monthly bills is small.