How To Use A Window Vac
Our five-step method for getting clear and streak-free windows with a cordless window vac and a cloth.
The short answer
To use a window vac, first wipe the glass with a damp cloth to lift loose grime, then spray it generously with window cleaning detergent and scrub any stubborn marks. Draw the window vac down the glass in straight, overlapping strokes from top to bottom so it sucks up the dirty water before it dries, and empty the tank down the sink when it fills.
A window vac does away with the bucket, squeegee and pile of towels. It sucks the dirty water off the glass as you go, so nothing drips onto the sill or runs down into streaks, and it works just as well on a small bathroom window as on a big set of patio doors.
For this guide we used the black Karcher window vac pictured, from our guide to the best window vacs for streak-free glass. The steps below work with any window vac, and the photos show a patio window going from grubby to clear.
What You'll Need
- A charged window vac
- A window cleaning detergent or the spray bottle that came with the vac
- A clean cloth or sponge cloth
- A microfibre cloth for the frame and edges
How To Use A Window Vac Step By Step
1. Wipe The Glass With A Cloth
Give the window a wipe with a damp cloth before the vac comes anywhere near it. This lifts the loose dirt, cobwebs and grit so the vac's rubber blade isn't dragging them across the glass. You'll be surprised how much comes away, and the cloth in our second photo is the result of just one window.
2. Spray On The Window Cleaning Detergent
Spray the glass generously with your window cleaner, covering the whole pane so there are no dry patches for the vac blade to skip over. Any window cleaning detergent works for this step.
3. Work The Detergent Into The Dirt
This step is optional on lightly dirty glass. On filthy windows, scrub the detergent in with a cloth to break down stubborn marks such as bird droppings and grease, which the vac then lifts away.
4. Pull The Window Vac Down The Glass
Start at the top of the pane and draw the vac straight down in one smooth stroke, keeping the blade flat against the glass. Overlap each stroke slightly with the last so you don't leave thin wet lines between them.
Work quickly enough that the soap doesn't dry on the glass, as dried detergent leaves the smears you're trying to avoid. On a hot or sunny day, spray and clear one pane at a time.
5. Empty The Tank
The dirty water collects in a small tank on the vac, and on a big job you'll need to empty it partway through. The water will be grimy, so pour it straight down the sink and rinse the tank before you carry on.
Tips For Cleaner Windows With A Window Vac
Using a window vac is simple, but a few extras make the job quicker. Charge it fully before a big session, as run time varies between models and a whole house of glass can outlast one charge. For upstairs windows, look for an extension pole that clips onto the vac. It saves dragging a set of telescopic ladders from window to window, and for really high glass a water-fed telescopic window cleaner keeps your feet on the ground.
Small panes and narrow leaded windows are easier with a smaller suction nozzle. Karcher sells a narrow 170mm suction nozzle for its WV 6 window vacs for exactly that, and other brands sell similar attachments.
Don't stop at the glass, either. Clean frames and sills make a big difference to how the whole window looks, so wipe the plastic over with a dedicated UPVC cleaner or diluted washing-up liquid once the glass is done.
You can watch our window vac at work in the Short below.
Window Vacs: The Easiest Way To Achieve Streak-Free Windows! We've Tested Multiple To Find The Best!
Window Vac Before And After
These two photos show the same patio window from inside, before cleaning and after the five steps above. The streaks, smears and marks in the first photo have gone, and the garden is clear through the glass in the second.
Is A Window Vac Worth Buying
A window vac can look like an unnecessary gadget, but once you've used one, going back to a bucket and towels feels like hard work. The glass dries clear in one pass and there's no dripping water to mop up afterwards.
It earns its keep in the bathroom too. Run it over shower glass and bathroom tiles after a clean and it clears the water before it can dry into limescale marks.
What People Also Ask Us
Do you need to use detergent with a window vac?
Yes, a window vac works best with a window cleaning detergent, because the vac only removes water and doesn't scrub. Spray the glass generously so the detergent loosens the dirt, then draw the vac down to suck it up. Plain water lifts light dust, but it leaves smears on greasy or dirty glass.
Why is my window vac leaving streaks?
A window vac leaves streaks when the blade isn't flat on the glass, when strokes don't overlap, or when detergent dries before the vac reaches it. A worn or dirty rubber blade causes the same problem. Wipe the blade clean, overlap each stroke slightly, work one pane at a time in sunshine, and replace the blade if it's nicked.
Can you use a window vac on the outside of windows?
Yes, a window vac works on the outside of windows as well as inside. Wipe off the heavier outdoor grime and cobwebs with a cloth first, as there's more of it outside, then spray and vacuum as normal. For upstairs windows, use an extension pole or a water-fed pole rather than working off a ladder with the vac in one hand.
Can you use a window vac on shower screens?
Yes, a window vac is very good on shower screens, glass doors and tiled walls. Running it over the glass after each shower removes the water before it dries into limescale spots, which keeps the screen clear for longer between deep cleans. Empty the tank afterwards so the water doesn't sit inside the vac.
Is a window vac really better than a bucket and squeegee?
For us, yes. The big difference is where the dirty water goes. A squeegee pushes it down onto the sill and the towels, whereas a window vac sucks it into the tank, so the glass is clear after one pass with nothing left to mop up. It's equally at home on a small bathroom window or a big set of patio doors.
Which window vac did you use for these photos?
The photos show a black Karcher window vac, one of the models covered in our guide to the best window vacs. You don't need the same one to follow along. The five steps work the same way with any window vac, so the method carries straight over if you own a different brand.
What's the best way to clean small panes and leaded windows?
Fit a smaller suction nozzle, as the full-width head is awkward on narrow panes and leaded lights. Karcher sells a narrow 170mm suction nozzle for its WV 6 models for exactly this job, and other brands sell similar attachments. Spray and clear one pane at a time so the detergent doesn't dry on the glass before the vac reaches it.
Do I have to scrub the glass before using the window vac?
Not on lightly dirty glass, where spraying and vacuuming is enough. The one step not to skip is a wipe with a damp cloth first, so loose grit and cobwebs don't end up dragged across the glass under the blade. Save the scrubbing for filthy windows, where working the detergent in breaks down bird droppings and grease for the vac to lift.
Richard has spent years renovating properties and turning them into rentals and Airbnbs. Like a lot of people he started out as a beginner, and these days there isn't much DIY he won't take on.