Window Condensation in Ottawa: Causes, Solutions, and When to Worry

# Window Condensation in Ottawa: Causes, Solutions, and When to Worry

# Window Condensation in Ottawa: Causes, Solutions, and When to Worry

Waking up to foggy windows on a cold Ottawa morning is common. But persistent or severe condensation can damage your home and indicate underlying issues.

## Understanding Condensation

### How It Forms

Warm, moist air hits cold surface → water vapor condenses into liquid.

**The dew point:** Temperature at which air becomes saturated and releases moisture. Colder surfaces below dew point = condensation.

### Where It Appears

**Interior glass surface:** Indoor humidity too high for current temperature.

**Between panes:** Seal failure (window needs replacement).

**Exterior glass surface:** Normal in some conditions (humid mornings).

## Normal vs. Concerning

### Normal Condensation

- Light fog at bottom of windows

- During/after high-humidity activities (cooking, showering)

- Clears within hours

- Occasional, not constant

- Only on coldest nights

### Concerning Condensation

- Heavy condensation running down glass

- Ice forming on interior

- Present most of the time in winter

- Causing water damage to sills

- Mold growth on frames or sills

- Between-pane condensation (seal failure)

## Causes of Interior Condensation

### High Indoor Humidity

**Sources:**

- Cooking (especially boiling)

- Showering/bathing

- Laundry (especially dryer venting issues)

- House plants

- Humidifier set too high

- Breathing (yes, really—family of 4 = 3+ liters/day)

- New construction/renovations (drying materials)

### Inadequate Ventilation

**Problems:**

- Bathroom fans not used or undersized

- Kitchen exhaust not venting outside

- Tight house without mechanical ventilation

- Blocked or disconnected vents

### Poor Window Performance

**Issues:**

- Single-pane windows (terrible in Ottawa)

- Failed double-pane seals

- Poor-quality windows

- Aluminum frames (conduct cold)

- Wrong windows for climate

### Other Factors

- Cold exterior temperatures (worse below -15°C)

- Window coverings trapping air against glass

- Interior air not circulating to windows

- Basement windows in high-moisture areas

## Solutions by Cause

### Reducing Humidity

**Target:** 30-40% relative humidity in winter.

**Actions:**

- Use exhaust fans when cooking/bathing

- Run bathroom fan 20+ minutes after shower

- Vent dryer outside (never inside)

- Reduce humidifier setting

- Open window briefly after high-moisture activities

- Consider dehumidifier

**Humidity monitor:** $15-$30, essential tool.

### Improving Ventilation

**Exhaust fans:**

- Size properly for room (bathroom: 1 CFM per sq ft minimum)

- Verify venting to outside (not attic)

- Use when needed, long enough

**Whole-house ventilation:**

- HRV (Heat Recovery Ventilator): Ideal for tight Ottawa homes

- ERV (Energy Recovery Ventilator): If humidity too low

- Cost: $2,000-$5,000 installed

**Air circulation:**

- Keep interior doors open

- Ceiling fans on low (reverse for winter)

- Don't block vents

### Improving Window Performance

**Short-term:**

- Interior storm windows or inserts

- Window film kits

- Cellular blinds (insulating value)

- Keep blinds partially open to allow air circulation

**Long-term:**

- Window replacement with proper glazing

- Triple-pane for Ottawa climate

- Low-E coating

- Warm-edge spacers

- Insulated frames (vinyl, fiberglass, wood)

**Window replacement cost:** $500-$1,500 per window installed.

### Improving Air Circulation

**At windows:**

- Don't seal windows with heavy curtains right against glass

- Leave gap at bottom for air movement

- Consider blinds instead of heavy drapes

- Registers should blow toward exterior walls/windows

## Between-Pane Condensation

### What It Means

Seal between panes has failed. Moist air has entered the insulated glass unit.

### What to Do

**Not repairable economically.** Options:

- Replace glass unit only (if frame is good)

- Replace entire window

- Live with it (still provides some insulation, but reduced)

### Should You Act?

**Replace if:**

- Multiple windows affected

- Significant visibility obstruction

- Planning to sell

- Condensation is heavy/constant

**Can wait if:**

- Just slight fogging

- Window otherwise performs okay

- Not planning to sell soon

- Only one or two windows

## When Condensation Causes Damage

### Signs of Water Damage

- Peeling paint on sills or frames

- Soft or rotting wood

- Mold on frames or walls

- Water stains on walls below windows

- Damaged drywall

- Flooring damage

### Preventing Damage

- Wipe up condensation regularly

- Check sills and frames periodically

- Address humidity source

- Improve window performance

- Repair damage early

### Mold Concerns

**If mold is present:**

- Clean small areas with appropriate cleaner

- Address underlying moisture

- Professional remediation for large areas

- Health concerns for sensitive individuals

## New Home/Renovation Considerations

### Why New Homes Often Have Issues

- Concrete, drywall, paint release moisture as they cure

- Very tight construction traps moisture

- Mechanical ventilation not yet balanced

- Materials drying for 1-2 heating seasons

### What to Do

- Run ventilation consistently

- Accept some condensation first winter

- Don't over-humidify

- Use exhaust fans aggressively

- Consider extra dehumidification

### After Major Renovations

Same issues—new materials, changed air sealing. Extra ventilation for first winter.

## Ottawa Winter Tips

### Extreme Cold (-25°C and below)

- Some condensation is nearly unavoidable

- Lower humidity more aggressively

- Accept temporary condensation on coldest nights

- Wipe up in morning

- Ensure heating reaches window areas

### Humidifier Settings by Outdoor Temperature

| Outdoor Temp | Maximum Indoor RH |

|--------------|-------------------|

| -10°C | 40% |

| -20°C | 35% |

| -30°C | 25-30% |

These are guidelines—adjust based on your windows and comfort.

### The Trade-Off

**Dry enough:** No condensation, but dry skin, static, respiratory discomfort.

**Humid enough:** Comfortable, but condensation on cold nights.

**Balance:** Some condensation on the very coldest nights is acceptable and often unavoidable without very low humidity.

## Summary

**For most Ottawa homes:**

1. Monitor humidity (keep 30-40% in winter)

2. Use exhaust fans properly

3. Ensure adequate ventilation

4. Wipe up condensation when it occurs

5. Consider HRV if tight house

6. Upgrade windows when replacement is due

Some condensation on the coldest nights is normal. Constant, heavy condensation signals a problem worth solving.