What are Drafty Windows and How to Stop it?

What are Drafty Windows?

Drafty windows are those that allow unwanted air to pass through, leading to energy loss, discomfort, and increased heating and cooling costs. This phenomenon can be explained through basic principles of physics.

What Causes Drafty Windows?

The causes of drafty windows are temperature difference, air pressure, conduction and windows design and materials. Let’s learn in detail why it causes drafty windows. 

Temperature Difference: The primary reason for drafts in windows is the temperature difference between the inside and outside of your home. According to the Second Law of Thermodynamics, heat flows from a warmer region to a colder one. 

Air Pressure: Air pressure is another factor. When there’s a pressure difference between the inside and outside of your home, air will move from the higher-pressure area to the lower pressure area. This can create drafts if there are gaps or openings in your windows. 

Conduction: In the case of poorly insulated windows, heat can be conducted through the glass itself. This means that warm air inside your home can directly transfer its heat to the colder air outside, leading to energy loss.

Window Design and Materials:

• Old, single-pane windows: These windows have a single layer of glass and often lack insulation, making them prone to draughts. 
• Damaged weatherstripping: Weatherstripping is the material that seals the gaps around your windows. If it’s damaged or worn, it can allow air to pass through. 
• Cracked or damaged caulk: Caulk is a sealant used to fill gaps around window frames. If it’s cracked or damaged, it can also allow air to pass through. 
• Poor installation: If your windows were not installed properly, they may have gaps around the edges that can let in drafts. 

How much can drafty windows increase your energy bills?

Drafty windows can significantly increase your energy bills, with estimates suggesting that they can lead to a rise in energy costs by 5% to 30%. To provide a clearer understanding of euros, let’s break down the potential financial impact. 

Energy Cost Estimates

Assuming an average monthly energy bill of €400 (approximately equivalent to $425), the additional costs due to drafty windows can be calculated as follows: 

5% Increase: 

Monthly: €400 * 0.05 = €20 

Annually: €20 * 12 = €240 

30% Increase: 

Monthly: €400 * 0.30 = €120 

Annually: €120 * 12 = €1,440 

How to Identify a drafty window?

You can often identify drafty windows by feeling the cold air near them or noticing condensation on the glass. To quantify the draftiness, you can use a draft detector or simply hold a lit candle near the window. If the flame flickers or is drawn towards the window, it’s a sign of a draft.

How to Stop Drafty Windows?

To stop drafty windows, you need to focus on sealing air leaks, improving insulation, and upgrading window materials. Here’s the scientific reasoning and practical steps you can follow: 

1. Seal Air Leaks Around the Window 

Reason: Drafts happen when there are gaps between the window frame and the wall, letting cold air in and warm air out. The rate of heat loss through these gaps depends on the size and location. 

Process: Use caulk to seal any gaps around the window frame. Caulk is best for cracks smaller than 1/4 inch. For larger gaps, weatherstripping is more effective. Apply it where the window sash meets the frame to stop drafts. 

Scientific value: Caulking and weatherstripping can reduce air leakage by up to 10-15% in typical homes. 

2. Improve Window Insulation 

Reason: Single-pane windows allow heat to escape easily because glass has a thermal conductivity of 1.0 W/m·K (watts per meter Kelvin), meaning it transfers heat quickly. 

Process: You can add insulating window film to reflect heat back into the room, or use thermal curtains to reduce heat loss through the glass. 

Scientific value: Window films can reduce heat transfer by about 35-45%, depending on the type. 

3. Install Storm Windows or Inserts 

Reason: A secondary window layer creates an air gap that acts as insulation, reducing heat transfer by conduction and convection. 

Process: Install storm windows or removable window inserts on the inside or outside of your window frame. These create a sealed air pocket that improves insulation. 

Scientific value: Storm windows can increase the R-value (a measure of insulation) of your window by 0.5–1.0, reducing drafts and improving overall energy efficiency. 

4. Use Draft Stoppers for Temporary Fixes 

Reason: Cold air can enter through the bottom of the window where the sash meets the sill. 

Process: Place a draft snake or a rolled-up towel along the base of the window to block the incoming cold air. This is a quick and inexpensive solution. 

Scientific value: While temporary, this can block up to 100% of the draft from this specific area. 

5. Upgrade to Energy-Efficient Windows 

Reason: Energy-efficient windows use low-E (low emissivity) coatings and multiple panes to reduce heat loss by reflecting infrared energy. The U-factor (rate of heat transfer) in double or triple-pane windows is much lower than single-pane windows. 

Process: If you want a long-term solution, consider replacing old windows with modern energy-efficient ones, like double- or triple-glazed windows with argon gas between panes. 

Scientific value: Double-glazed windows have a U-factor of around 0.3, compared to 1.0 for single-pane windows, cutting heat loss by 50-70%. 

Proper Process to Fix Drafty Windows: 

• Inspect all windows for gaps, cracks, and poor seals. 
• Apply caulk or weatherstripping to close air leaks around frames and sashes. 
• Add insulation with window films or thermal curtains. 
• Install storm windows or inserts for extra insulation. 
• Upgrade your windows if you have the budget, choosing energy-efficient models.