Window Cleaning in Toronto: Hard Water Spots, Low-E Coatings and What Not to Scrape
Window cleaning looks like the simplest job in the house. Glass, a cloth, something blue in a spray bottle. It is also the one surface where the most widely repeated advice - vinegar, newspaper, a razor blade for the stubborn spots - is the advice most likely to leave permanent damage behind.
Part of the reason is that the advice is old. It was written for plain, uncoated single-pane glass, the kind Toronto houses were built with a century ago. Most of the glass in this city is no longer that. Any window replaced in the last two decades, and effectively every unit in a new condo tower, carries a microscopically thin low-emissivity coating, and coated glass has its own published care rules that almost nobody outside the glazing trade has read.
The other reason is local. Toronto tap water is measurably hard, so the rinse water itself leaves a mark. Add road salt on ground-floor sashes, a heating season that drives condensation onto the coldest surface in the room, and a spring of construction dust, and window cleaning here becomes a timing problem as much as a technique problem. This guide covers both: what the glass industry actually says, what Toronto adds to it, and the order of operations that gets glass clean without costing you a coating.
Why Toronto Windows Are Harder Than the Internet Assumes
Three things separate a Toronto window from a generic one, and all three change what you should put on the glass.
The first is the water. The City of Toronto's 2025 drinking water analysis summary puts average hardness at 119 mg/L as calcium carbonate, with a range of 115 to 122 mg/L, against an aesthetic objective of 80 to 100 mg/L. Average pH is 7.5. In plain terms, the water coming out of the outdoor tap carries more dissolved mineral than the guideline range, and every drop of it left to evaporate on glass deposits that mineral in place.
The second is the glass itself. Natural Resources Canada puts windows, doors and skylights at up to 35 percent of total house heat loss, and credits low-emissivity coatings with reducing winter heat loss and summer heat gain by up to 50 percent. That coating is the entire reason a modern Toronto window outperforms the sash it replaced. It is also a surface with a chemistry and abrasion tolerance that ordinary float glass does not have.
The third is the weather. Brine splash from the road and sidewalk coats basement and ground-floor windows all winter. Freeze-thaw cycling pulls moisture through every gap. Then the furnace runs for six months and the glass becomes the coldest surface in the room, which is where the indoor moisture goes.
What the Glass Industry Actually Says About Cleaning Glass
The glass trade publishes its own bulletin on this, Proper Procedures for Cleaning Architectural Glass Products, and the fabricators who make coated units publish care guidance alongside it. Four of those instructions contradict the most popular household advice outright.
Do Not Scrape
The bulletin is unusually blunt. The industry, it says, neither condones nor recommends widespread scraping of glass surfaces with metal blades or knives, and it instructs readers not to use scrapers of any size or type for cleaning glass. The only exception it carves out is a new one-inch razor blade, on small isolated spots, on uncoated glass, worked in a single direction. Its verdict on anything larger: using 2, 3, 4, 5 inch and larger blades to scrape a window clean carries a large probability of causing irreparable damage to glass.
Coated glass gets a further warning from the fabricators. On heat-strengthened or tempered glass, even a plastic scraper can dislodge very small surface debris that fused to the glass during heat treating, and drag it across the pane. Tempered glass is standard in patio doors, sidelights and any pane near a walking surface - which is to say, exactly the glass that collects paint flecks, price stickers and tape residue.
Do Not Use Abrasives or Harsh Chemistry
The manufacturer guidance is explicit: do not use harsh cleaners, abrasives or alkaline materials, and do not use any additive containing hydrofluoric acid or capable of forming it. The bulletin adds a subtler point that matters more in practice - do not allow abrasive particles to become trapped between the glass and the cleaning material. A sponge dropped on a patio, a cloth washed with grit still in it, or a microfibre pad used on a gritty sill and then carried to the glass all become sandpaper.
That rules out scouring powders and melamine foam pads, which work by micro-abrasion. On a painted wall they leave burnished patches; on coated glass they take the coating with them.
The Vinegar Problem on Coated Glass
This is the one that surprises people. The care guidance for coated glass states that acidic cleaning solutions are not recommended and that only mild soaps or detergents should be used, and it rules out abrasive cleaners, fluoride salts and hydrogen-producing compounds as well. Vinegar is dilute acetic acid. On plain uncoated glass it is harmless. On a coated surface, the industry position leaves no room to argue.
The usual reassurance is that the low-E coating sits on an internal surface inside the sealed unit, protected from your cloth. That is often true and not always true: some coatings and applied films sit on an exposed face, and you cannot tell which you have by looking at the pane. Given that, mild detergent is the safe default for the whole house, and the cost of that default is essentially nothing.
It matters because damage to a coating does not look like a scratch. The fabricators describe it as coating removal and a visible change in light transmittance - a haze, or a patch that reads slightly different from the rest of the pane in raking light, and never cleans off again.
Test First, and Never in Full Sun
Both sources ask for the same two habits. Test-clean a small area of one window before starting the whole project, and evaluate glass surfaces in daylight rather than under a work light. And avoid cleaning tinted or reflective glass in direct sunlight, because the surface may simply be too hot to get a satisfactory result.
The practical version of that second rule: in full sun the solution flashes off before the squeegee reaches it, and you get exactly the streaking you were trying to avoid. South and west elevations are morning jobs in a Toronto summer.
The Method That Actually Works
Put the bulletin's own sequence together and the method is close to the opposite of spray-and-wipe.
1. Dry-remove the grit first. Brush or vacuum the frame, track and sill before any water touches the glass. This is the trapped-abrasive rule in practice - most window scratches start as dust that was on the cloth, not on the pane.
2. Flood the glass, do not wipe it. Soak the surface with clean water and a mild soap solution to loosen the dirt. The wash solution is there to act as a lubricant that floats loose debris off the glass. A spray bottle puts down too little liquid to float anything; it redistributes the grit and then you rub it in.
3. Apply with a non-abrasive applicator. A brush or a strip washer, agitated lightly. Generous solution, light pressure.
4. Rinse with liberal clean water. Immediately, before anything starts to dry.
5. Squeegee promptly, working top down. Overlap each pull by an inch or so and wipe the blade between passes. The squeegee is not a finishing flourish - it is the step that removes Toronto's dissolved mineral before it can dry in place.
6. Dry the residue off gaskets, sealants and frames. Water sitting in a sash carries the same 119 mg/L of mineral as water on the glass, and it sits there far longer.
Work top down across the pane, top down across the window, and top down across the house, so nothing you have already finished gets rinsed on twice.
One more note on tools. A squeegee blade is a consumable. A nicked or hardened rubber lays down a fine line on every pull and no amount of buffing fixes it; replace the rubber rather than the technique.
Hard Water Spots, and Why a Quick Rinse Makes Them Worse
At an average of 119 mg/L, above the 80 to 100 mg/L aesthetic objective, Toronto water leaves a visible deposit whenever it is allowed to evaporate on a smooth surface. This is why hosing off the outside of a window and walking away produces a worse-looking result than not washing it at all. You have effectively applied a thin, even coat of dissolved limestone and then let it dry.
Where that has happened repeatedly over years, the pattern on window glass is the same one that shows up on a shower enclosure, and so is the crucial distinction: mineral sitting on the surface can be dissolved and removed, while glass that has been etched by long mineral contact cannot be cleaned at all, because there is nothing left to remove. We walked through how to tell those two apart in our guide to cloudy Toronto shower glass, and the test is identical on a window.
If the glass is uncoated, a dilute acidic descaler will dissolve surface carbonate. If it is coated, or if you are not certain, the guidance rules that out and you are left with mild detergent, mechanical patience and repeated passes - which does work, slowly, on deposit that has not yet etched.
The more useful fix is upstream. Sprinkler overspray hitting a ground-floor window, a downspout splashing a basement pane, and a window directly under an unguarded eave are the three repeat offenders in Toronto homes. Redirect the water and the glass stays clean for a season instead of a fortnight.
Winter Condensation, Sills and Mildew
Natural Resources Canada describes the mechanism plainly: condensation forms in colder weather when moist indoor air comes into contact with cooler surfaces, and the risk increases as the weather gets colder and the inside humidity rises. It can appear on the glass, on frames and sashes, on weather seals, on the wall around a skylight, and between the panes if the sealed unit has lost its seal.
That last location is worth separating out immediately, because it is the one case where cleaning is not the answer. Fog between the panes of a sealed unit means the seal has failed and moisture is inside the cavity. There is no accessible surface to clean. It is a glazing repair, not a cleaning task, and no product will touch it.
For condensation on the room side, Natural Resources Canada names a cause people rarely connect to it: blocking air circulation with deep window sills, closed drapes and blinds, or furniture pushed up against a window allows cool air to pool at the glass, which brings the surface temperature down and invites condensation. A heavy curtain drawn across a Toronto bay window for the whole of January is, functionally, a condensation generator. Leaving blinds cracked and pulling the sofa forward a few inches does more than any spray.
The damage shows up in the sill. Water runs down the glass, collects in the sill and the bottom of the sash, and a painted or wood sill left damp week after week grows mildew along the caulk line. The treatment there is the same one we set out for mildew on painted surfaces - wipe the water away as a habit through the heating season, and treat the growth rather than painting over it.
Indoor humidity is the other lever, and it is the one that solves the problem rather than managing the symptom. The relationship between moisture, ventilation and mould in a closed-up house is the same one that drives mould growth through a humid Toronto summer, just running in the opposite direction, and it connects directly to how your heating system moves and recirculates winter air.
Finally, a piece of reassurance that saves a lot of unnecessary service calls. Natural Resources Canada notes that low-E coatings can actually increase the chance of condensation forming on the outside of the glass at sunrise, when conditions are cool and calm and the air is humid. Homeowners see fog on the exterior of a window they just paid to replace and assume it is defective. It is the opposite: the outer pane is staying cold because the coating is keeping the heat inside where you paid to put it.
Screens, Tracks, Frames and the Concrete Problem
Cleaning the glass and ignoring everything around it is why windows look dirty again within a week.
Screens. A screen holds pollen, brake dust and construction dust, and glass washed behind a loaded screen re-dirties in the first rain. Take them out, lay them flat, work with a soft brush and mild detergent, rinse, and let them dry completely before reinstalling. Pressure is what bends frames and stretches mesh, so there is no fast version of this.
Tracks. Vacuum before you introduce any water. Grit in a slider track is abrasive against both the frame and any cloth you carry to the glass, and it is usually the reason a patio door has become stiff.
Weep holes. The small slots at the bottom of an exterior frame drain rainwater out of the sash. Blocked with debris, they let water back up inside the frame instead. A vacuum and a bent paperclip clear them in a minute, and it is worth doing before winter.
And one Toronto-specific hazard the bulletin singles out: concrete or mortar slurry that runs down or is splashed onto glass is especially damaging and should be washed off as soon as possible. Balcony slab repairs, tuckpointing, parging, a driveway pour, a neighbouring site - any of those upstream of a window means rinsing that glass the same day, with plenty of water, not at the end of the project. Alkaline slurry left to cure on glass does not simply wipe off later.
When to Clean Windows in a Toronto Year
The manufacturer guidance for coated glass asks for frequent cleaning, at a minimum of three to four times annually. Mapped onto this climate, that lands naturally on four moments.
Early spring, after the salt. Ground-floor sashes and basement windows carry a winter of brine splash, and salt film holds moisture against the frame long after the snow is gone.
Late spring, after the pollen. Screens out, screens washed, glass done behind them.
Late summer into early fall. The important one. Clean glass and dry, sound sills before the furnace comes on, because everything that runs down a window between November and March lands on whatever you left in the sill in September.
Mid-winter, interior only. A light pass on the room side during condensation season, mostly to keep the sills dry and catch mildew early.
If you already book a seasonal reset, windows, sills, tracks and screens fold naturally into a deep cleaning visit rather than becoming their own separate afternoon. Given that the glass is carrying a coating credited with up to a 50 percent reduction in winter heat loss, it is worth the small discipline of cleaning it the way the people who make it ask you to.
Sources and Research
Cleaning method, scraper guidance and the warning about concrete and mortar slurry come from the glass industry bulletin Proper Procedures for Cleaning Architectural Glass Products, which sets out the wash-rinse-squeegee sequence, the restriction on metal blades, and the instruction not to allow abrasive particles between the glass and the cleaning material.
The guidance on coated glass - mild soaps or detergents only, no acidic cleaning solutions, no abrasives, fluoride salts or hydrogen-producing compounds, no hydrofluoric acid, the caution about plastic scrapers on heat-treated glass, cleaning at least three to four times a year, and the description of coating damage as a visible change in light transmittance - comes from Clarity on Proper Glass Cleaning, published by an architectural glass manufacturer.
The figures on heat loss and coating performance - windows, doors and skylights accounting for up to 35 percent of total house heat loss, and low-E coatings reducing winter heat loss and summer heat gain by up to 50 percent - come from Natural Resources Canada's Keeping the Heat In, Section 8. The condensation mechanism, the effect of deep sills, closed drapes and nearby furniture on air circulation, and the note about exterior condensation on low-E glass at sunrise come from the same department's guidance on window condensation.
Toronto water hardness figures - an average of 119 mg/L as calcium carbonate across a range of 115 to 122 mg/L, against an aesthetic objective of 80 to 100 mg/L, at an average pH of 7.5 - are taken from the City of Toronto's Drinking Water Analysis Summary 2025.
A Word from Custom Maids Toronto
(Sponsor of the Article)
Custom Maids Toronto has been cleaning homes in this city for more than 48 years - long enough to have watched the same houses go from single-pane sashes with storm windows to sealed low-E units, and long enough to know that the cleaning advice did not update when the glass did.
One detail matters more on glass than almost anywhere else in a home: Custom Maids does not supply the cleaning products. You do. That means nothing reaches your windows that you did not choose. If your glazing is coated, you can hand our team the mild detergent the manufacturer asks for and know with certainty that no acidic descaler, no scouring powder and no unlabelled spray is going anywhere near that coating.
If you would rather hand the seasonal window list to someone else - glass, sills, tracks and screens, in the right order - you can reach the team at Custom Maids Toronto and tell us exactly what you want used in your home.
Frequently Asked Questions
Is vinegar safe for cleaning windows?
On plain uncoated glass it is a mild acid and generally harmless. On coated glass the manufacturer guidance is that acidic cleaning solutions are not recommended and only mild soaps or detergents should be used. Because a coated pane and an uncoated one look identical, mild detergent is the safe default for the whole house.
Can I use a razor blade to get paint or a sticker off a window?
The glass industry bulletin says not to use scrapers of any size or type for cleaning glass, and allows only a new one-inch blade, on small isolated spots, on uncoated glass, worked in one direction. On tempered glass even a plastic scraper can drag fused surface debris across the pane. For coated or tempered glass, soften the deposit with detergent and give it time instead.
Why do my windows streak even with a good cleaner?
Usually too little liquid and too much sun. Flooding the glass with a mild soap solution floats debris off the surface; a light spray just moves it around. And cleaning tinted or reflective glass in direct sunlight lets the solution dry before the squeegee reaches it, which produces the streaks you were trying to prevent.
What are the white spots that will not wipe off?
Mineral deposits from hard water. Toronto's 2025 water analysis puts average hardness at 119 mg/L as calcium carbonate, above the 80 to 100 mg/L aesthetic objective, so water left to air-dry on glass leaves that mineral behind. If it resists dissolving, the glass may be etched, which is permanent.
Why is there condensation on the outside of my new windows?
Natural Resources Canada notes that low-E coatings can increase the chance of exterior condensation at sunrise when the air is cool, calm and humid. The outer pane stays cold precisely because the coating is holding heat inside. It is a sign the window is working, not failing.
There is fog between the panes. Can that be cleaned?
No. Condensation inside a sealed unit means the seal has failed and moisture is in the cavity between the panes. There is no accessible surface to clean, and no product reaches it. That is a glazing repair.
How often should windows actually be cleaned?
Manufacturer guidance for coated glass asks for frequent cleaning, at a minimum of three to four times a year. In Toronto that maps to after the winter salt, after the spring pollen, before the furnace season starts, and a light interior pass mid-winter.
Do I really need to take the screens out?
For anything beyond a quick interior wipe, yes. A screen holds pollen and road dust, and glass cleaned behind a loaded screen dirties again in the first rain. Lay screens flat, use a soft brush and mild detergent, and let them dry completely before they go back in.
Can I pressure wash exterior windows?
It is a poor idea. Pressure drives water past weather seals and into the sash, and it can push grit across the glass at speed. Flood the surface, wash with a non-abrasive applicator, rinse generously and squeegee instead.
