Ottawa Window Condensation: Inside, Outside & Between Panes

Sep 08, 2025

Waking up to fogged glass isn’t a character flaw. It’s physics tapping on the frame. In Ottawa, the question isn’t if you’ll see moisture — it's where and when. That location tells you the fix. This guide sorts out window condensation Ottawa complaints into three buckets (inside, outside, between panes), then walks you through targets, tools, and next steps. Short, practical, and local.

Key takeaways

Inside (room-side): indoor humidity too high or airflow blocked; solve with ventilation, dehumidification, better air wash at the glass, and warmer inner-pane temperatures.
Outside (street-side): morning dew on efficient low-E glass is normal most of the time.
Between the panes: likely a failed seal in the IGU — book inspection and plan IGU replacement.
Winter humidity Ottawa: aim for ~30–40% RH; during extreme cold, drop temporarily to prevent frosting.

Quick Diagnosis Table

Where you see moisture	What it means	Common in Ottawa when	What to do
Inside (room-side)	Indoor RH too high; weak airflow; inner glass too cold	Winter mornings; after showers/cooking; blinds closed tight	Run bath/kitchen fans 15–20 min; use a dehumidifier; tune HRV/ERV; open blinds a bit; keep heat registers clear; consider low-E/triple-pane for warmer inner glass
Outside (street-side)	Morning dew on high-efficiency glass (radiative cooling)	Cool mornings after warm days; clear skies; sheltered façades	Usually normal; trim vegetation; allow sun/breeze; check sills for drainage if water lingers
Between panes	Failed IGU seal; gas loss; desiccant saturated	Any season; looks like haze or droplets trapped inside	Schedule inspection; replace the sealed unit (warranty?); or upgrade sash/frame if near end-of-life

Ottawa-Ready Humidity Targets (and Why)

Condensation happens when glass temperature dips below your indoor dew point. Lower the dew point (reduce RH) or raise glass temperature — those are the levers.

Winter comfort target: ~30–40% RH for most homes.
During cold snaps (−20 to −30 °C), lean lower for a few days to stop edge frost.
Year-round living: 30–50% RH works well for people, pets, and woodwork.

You can’t manage what you can’t see. Buy two inexpensive hygrometers and park them in different rooms. Track morning and evening readings for a week. You’ll spot patterns: spikes after showers, a bedroom that runs wetter with the door closed, a plant corner that tips the balance.

Quick cue: if the inside of a north window fogs while the rest stay clear, that room’s humidity or airflow is the outlier — not the whole house.

Step-by-Step — Reduce Interior Condensation

Tools: 2 hygrometers, a simple timer, microfibre cloths.
Timeframe: one week to tune habits and settings; the payoff is immediate comfort.

Vent the sources first.
Cooking, showers, laundry — these are humidity bombs. Run kitchen and bath fans 15–20 minutes beyond use. Put a timer or smart switch on them so “I forgot” isn’t the reason your windows sweat.
Set your HRV/ERV for winter reality.
In cold weather, an HRV (heat-recovery ventilator) exchanges stale indoor air for dry outdoor air while keeping most of the heat. Ensure it’s clean, balanced, and not stuck in a summer setting. An ERV moderates moisture more gently — fine, but you may still need a dehumidifier during cold snaps.
Use a dehumidifier strategically.
Basements and tight bedrooms accumulate moisture. Run a dehumidifier to hit your target RH, then let the HRV maintain it. Empty the tank daily at first; once you see the trend, set a schedule.
Wash the glass with warm air.
Don’t trap cold air next to the pane. Keep registers and radiators unblocked. Open blinds or raise them 2–5 cm so warm air can reach the glass face. Heavy drapes? Leave a gap at the top and bottom.
Warm the glass itself.
If your units are older, a modern low-E coating and argon fill raise inner-pane temperature. Triple-pane magnifies that effect and improves condensation resistance. Heritage home? A low-E storm panel creates a thermal cavity without changing the original sash.
Lifestyle tweaks that add up.
Lids on pots. Shorter hot showers. Spread laundry days out. Cluster plants away from the coldest façades. Small changes; big RH effect in a tightly built home.
Daily wipe on high-condensation days.
When the temperature plunges overnight, use microfibre to clear beads at dawn. It’s not the cure — steps 1–6 are — but it protects wood sills and trim while your new routine settles.

Outside Condensation — A Good Sign

You step outside, the lawn is wet, and your efficient windows look misted over on the street-side. That’s radiative cooling at work: clear night sky, glass radiates heat, outer surface drops below ambient air temperature, moisture condenses. Ironically, you notice this more on high-performance units because they hold indoor heat so well.

When to relax: light dew that burns off mid-morning.
When to take a look: persistent wetness that hugs sills through the day, visible algae or staining, or water pooling because shrubs block sun and airflow. Trim the greenery; check sill slope and drainage paths.

Between the Panes — Failed Seal

Moisture inside the insulating glass unit (IGU) is another story. You can’t wipe it away. Sun may shift the pattern, but the haze and droplets return. That’s a failed seal: the perimeter sealant or spacer has given up, argon (or krypton) has escaped, and the desiccant is saturated.

What it means:

Clarity drops. A permanent fogged window isn’t pleasant, especially on feature views.
Efficiency slips. Gas loss and moisture reduce performance; the inner pane runs colder.
Ventilation won’t fix it. The problem is sealed inside the unit.

Your options:

Sealed-unit replacement (IGU replacement). A new IGU is ordered to size and installed into your existing sash if the frame is sound. It’s often faster and more economical than full window replacement.
Sash/frame upgrade. If the frame, hardware, or weatherstripping is near end-of-life — or you want the benefits of triple-pane and warm-edge spacers — step up to a full unit.
Warranty check. Many manufacturers cover IGUs for a defined period. We inspect, document, and process the claim where applicable.

Typical process: site inspection and measurements → order the IGU → installation appointment. Minimal disruption. A clear view again.

FAQs

Can new windows still sweat inside?
Yes. Even high-performance units can fog on the room-side if RH is high and airflow is blocked by blinds or furniture. Tuning ventilation and a small RH reduction usually solves it.

What winter humidity should I keep?
For Ottawa, ~30–40% RH is the sweet spot. During a deep freeze, drop a little lower for a few days to prevent edge frost.

Do trickle vents help?
They can, but they’re a coarse tool. A balanced HRV/ERV plus targeted fan use is more effective and keeps heat where you’ve paid for it.

Will triple-pane stop condensation?
It won’t change your RH, but it raises inner-pane temperature, which increases condensation resistance. Pair triple-pane with good humidity control for the best outcome.

Is interior condensation dangerous?
Occasional light fog that clears is a nudge, not an emergency. Persistent beads running onto sills can damage finishes, grow mould on caulking, and signal ventilation issues. Act before it becomes a repair bill.

Can I fix “between-pane” fog without replacing the glass?
No practical, durable fix from the room side. IGU replacement is the reliable route; consider a sash/frame upgrade if the unit is older or you want better winter comfort.

Putting it all together (and what we can do)

Inside condensation: reduce RH, improve airflow, and warm the glass surface.
Outside condensation: usually a compliment to your glass; keep surroundings tidy and draining.
Between-pane fog: book inspection; plan an IGU replacement or upgrade.

If your window condensation Ottawa checklist points to a failed seal or you’re curious whether low-E or triple-panewould calm a stubborn room, we can help. We’ll measure, check frames and spacers, confirm dew point/RH realities with a hygrometer, and recommend the right path — sealed-unit swap, targeted replacements, or a full upgrade with warm-edge spacers and modern frames. Financing and warranty guidance available.