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Interior Condensation

New windows are more energy efficient and a much more air tight, putting a stop to your heating dollars escaping out those loose fitting drafty windows. Along with new energy efficient, tighter fitting doors and adding extra insulation in the attic, our homes are becoming very air tight, not allowing that warm moist air to escape any more. Glass is the coldest surface on the outer walls of your home and as heat goes to escape it will condensate on the coldest surface which is the bottom of any thermo pane of glass.

Decorative internal grilles and internal mini-blinds are constructed out of metal which will also conduct the cold, increasing the potential for interior condensation.

High performance glass reflects that radiant heat that is trying to escape through the windows, back into the house, warming the glass surface as the heat rises. Now as the room air starts to cool it begins to fall to the floor to find its way back to the furnace by way of the return air vents. As the warm air cools, it falls down across the interior surface of the window. The air contacts the horizontal meeting rail of the DH window, which acts like a dam, slowing the airs rate of fall and creating an opportunity for the trapped water vapour to escape and form on the meeting rails surface. The air then rolls over the meeting rail and gains speed until it encounters the lower sash hand rails or window frame. At this point the water vapour once again makes its exit and condensates on the bottom of the sash.

Double pane Low-e and argon gas provides a warmer interior glass surface than a standard air filled thermo- pane.

Triple pane, with two Low-e and krypton gas provides the warmest interior glass surface to lower the possibility of condensation.

Condensation will still occur on even the highest insulating glass for two reasons. The relative humidity in the home is too high for the outside temperature and/or the interior glass surface is getting colder because curtains or blinds are too tight fitting and not allowing the warm air to circulate around the window to keep it warm.

The style of window can also contribute to more or less condensation, such as vertical and horizontal sliding product versus casement, fixed or awning style.

Casements, awning and fixed windows do not take on rain water, and also clamp shut when closed and therefore do not require drainage holes to expel the rain water. These windows clamp shut and compress the weather stripping, providing the tightest seal against air infiltration.

Vertical and horizontal sliders do take on rain water and require drainage weep holes to expel the water. Sliding sashes have fur weather stripping and interlocks at the meeting rails to reduce air infiltration in colder weather when closed, while being able to slide open in milder weather for ventilation.

These drainage systems and weather seals by design, allow some cold outside air to infiltrate back into the home. This air gets trapped when curtains or blinds are too tight not allowing proper air circulation, contributing to a colder glass surface.

Now the little amount of warm moist air that sneaks around the tight fitting blinds, hits the colder glass and condensates. Notice when you open the blinds the room air is allowed to circulate and warm up the glass and the extreme condensation starts to evaporate.

Yes you can. by addressing the humidity levels in your home. Remember, the condensation will not damage your new windows as there is no wood to be affected.

Condensation is unavoidable when the outside temperature drops quickly by 10 to 20 degrees overnight and the indoor relative humidity is now too high.

A little condensation is to be expected, a lot is not and will turn to frost or even ice and therefore you may need to reduce the humidity levels in the home.

The main source of humidity in a typical home is from regular household activities, which will vary with the living habits of the family.

A family of six people will produce much more moisture in the home than a family of two. Typically 7 to 9 litres of moisture per day is introduced into a house with a family of four, under normal conditions, which can rise to 20 or more litres on laundry day.

Activities such as showers, laundry, cooking, plants and humidifiers all contribute to adding moisture. Turning the thermostat down a few degrees at certain times during the day, especially in extreme cold weather, greatly contributes to high humidity levels in an active home.

You need the heat on to dry the moisture out, otherwise all that moisture you are creating is being absorbed by your carpets, upholstery and walls and you will never dry the moisture out.

There are many reasons for high humidity levels in the home and the sources of moisture can be reduced or controlled through continuous air movement, ventilation and keeping the heat at a consistent warm temperature in the very extreme or fluctuating cold weather.

Ouside Air Temp (°C) Maximum Indoor Relative Humidity at 20 °C (68°F)
-30 °C or below 15%
-30 °C to -24 °C 20%
-24 °C to -18 °C 25%
-18 °C to -12 °C 35%
-12 °C to   -0 °C 40%

Follow these steps listed below and you will decrease and control condensation:

Standard solutions

  1. Shut off furnace humidifiers and other humidifying devices in your home.
  2. Keep the humidity level lower by 10% than the current outside temperature recommends allowing for that 10-20 degree drop over night. The moisture in the house will not dry up fast enough and condensation will occur.
  3. Change to a two speed furnace fan or leave your current fan on manual during extreme colder weather. Continually move the air even when the heat turns off. This will eliminate the fluctuation in room temperature, providing more comfort and reducing moisture in the home.
  4. Use exhaust fans when showering and cooking, directly venting to the outside of the home. Open the bathroom window when showering to expel the moisture immediately.
  5. Turn your thermostat up a degree or two and leave it there. You need heat to dry out the moisture, especially in an active busy household.
  6. In newer homes cold air returns are in every room. In older homes the cold air returns are only in the hall ways. If this is the case, make sure the bedroom doors are not touching the carpet and are at least 1 ½” off the floor, or leave the doors open all the time. Hot air rises and cold air falls to the floor, travels along the floor to the return air vents back to the furnace.
  7. Curtains and blinds need to be 3″-4″ away from the window, 1″ away from the sides and bottom. They should also be louvered and not solid to allow room air to warm the window glass surface. When the lights go off at night, or any time you can, you should open up the window blinds and curtains to allow the room air to keep the window surface warm, reducing condensation.
  8. Open your windows once a day while in the room, for a few minutes to allow the warm moist air to be replaced by the cooler dry air from outside. Warm air takes longer for the furnace to heat than dry air.

Advanced or Technical Solutions

  1. Be sure that the ventilating louvers in your attic, basement or crawl spaces are open and correctly sized.
  2. Update your furnace fan to a two speed fan motor. The fan stays on when the heat burner shuts off, reducing to a lower speed, continually moving the air throughout the house. This keeps the temperature more consistent and reduces humidity.
  3. Installing a Heat Recovery System (HRS), air exchanger, to the furnace which not only reduces or eliminates condensation, it removes dust, pollen and mould spores. This system exchanges all the air in your home many times per day. An HRS would be a standard requirement on the most air tight energy efficient homes being built today.
  4. Make sure the vents to gas burners, clothes dryers, etc. vent directly to the outdoors.
  5. Remove the dryer vent hose once a year and check to see that it is not plugged solid with lint.
  6. Open fireplace dampers to allow an escape route for moisture-laden air.
  7. Reduce the number of indoor plants.
  8. When renovating and the walls are torn out, install cold air returns in every room.

Exterior Condensation

Exterior condensation occurs during late summer and early fall, when days are warm and humid and nights are cool and clear. Moist air comes into contact with cool surfaces, such as glass. This type of condensation appears when the dew point in the air is higher than the temperature of the outside pane of glass.

Windows on elevations blocked from the wind, large bushy flower gardens, holding lots of moisture beneath a window and along with also being protected from the sun for the early morning hours, all contribute to exterior window condensation.

This is phenomenon is increasing as windows improve the efficiency of high performance insulating glass. Existing air filled thermo panes would allow the warm inside temperature to transfer through the glass to the cooler outside surface and warm up the glass. No condensation.

Your new high performance Low-e and Argon gas glass today, especially with triple glass using two Low-e and Krypton gas, the heat loss or transfer is dramatically reduced.

These high insulating glass windows contribute to a cooler outside pane of glass which condensates for a few hours in these atmospheric conditions. Evidence of a well insulated window.

Once the outside temperature warms up or a wind picks up the condensation disappears.

No harm is done, other than an annoying temporary loss of view.


Low-E (emissivity) Glass
Low-E glass has a metallic (metal) oxide coating applied onto the surface (soft coat) or is applied into the glass (hard coat). This smart glass technology allows the short-wave energy (light from the sun) to pass through while reflecting the long-wave energy (radiant heat) back to its source.Consumers guide 7.1

Low-E glass reflects more radiant heat (temperature) and allows less solar gain from the sun.

Low-E glass reflects less radiant heat (temperature) and allows more solar gain from the sun.

Heat Mirror
Low-E films are sheets of transparent polyester suspended inside the cavity between the glass panes, also filled with argon or krypton gas. This glass unit achieves the ultimate in insulation values. Consumers guide 7.3

Radiant heat
The heat produced by your furnace in the winter. In the summer when light from the sun hits a solid surface such as the asphalt, concrete or brick it produces heat.

Solar heat gain
The heat that is produced when the light from the sun rays pass through your window, hits the floor or furniture and warms the objects.

Argon gas
An inert gas which is 6X heavier than air and when combined with Low-E glass in a double thermal pane unit it increases the insulating value by twice as much. Consumers guide 7.1

Krypton gas
Inert gas which is 12X heavier than air, when combined with Low-e glass in a triple thermal pane unit it increases the insulating value by 5 times as much. Consumers guide 7.1

Double glazed glass
Two panes of glass separated with a warm edge spacer bar creating one air/gas chamber. Eliminating condensation between the panes of glass and providing improved insulating properties. Consumers guide 3.3

Triple glazed glass
Three panes of glass separated with two warm edge spacer bars creating two air/gas chambers. Eliminating condensation between the panes of glass and providing superior insulating properties. Also proving a warmer interior glass edge to reduce or eliminate due point condensation in the heating season. Consumers guide 3.3

Foam insulated
Frames and sashes will further decrease heat loss by improving thermal performance. Consumers guide 3.5, pg 14

Radiation losses
Radiation through the window glass represents about two thirds of the total heat loss in a standard window. Because ordinary glass readily emits heat to colder surfaces (i.e., has a high emissivity), radiation losses can be reduced by lowering the emissivity of the glass (hence the term low emissivity or low-E glass). Consumers guide 4.2

Conduction losses
Conduction in a window occurs primarily through the edges and frames of the unit. Advances in materials and designs that more effectively use insulating materials have dramatically reduced these losses. Consumers guide 4.2

Convection losses
Convection occurs due to air movement between the spaces of multi-glazed windows. If the space is too small, conduction through the air is significant. If the air space is too large, the still air will begin to rise as it is heated on the warm interior side, and fall as it is cooled on the cold exterior side of the window. This convection movement of the air passes heat to the exterior. The best spacing using argon gas to minimize convection losses is 1/2″-5/8″ between the panes of glass, and using krypton gas would be 5/16″-3/8″ spacing. Consumers guide 4.2

ER rating (Energy Star)
A measure of a window or doors overall performance, based on three factors: 1) solar heat gains from the sun; 2) minus heat loss through frames, spacer and glass; 3) minus air leakage heat loss. Consumers guide 6.3

The measurement of the rate heat is lost through a material or product. The lower the number the slower the rate of heat transferred the better the insulating value. 1 divided by an imperial U-value equals the R-value. Therefore 1 divided by U-value of 0.1 = R-value of 10.

Is a measurement of resistance to heat loss through a material or product. The higher the number the slower the rate of heat transferred, the better the insulating value.

SHGC (solar heat gain coefficient)
This is the measurement the amount of heat that is blocked by the sun. The lower the SHGC number, the more the heat from the sun is blocked, better performance to reduce air-conditioning costs.

VT (visible light transmittance)
The measurement of visible light transmitted through the glass. The lower the VT number is the less visible light.

CR (condensation resistance)
The measurement of how well a product resists condensation in normal conditions. The higher the CR number is the better the resistance.

Double Hung Window (Vertical Slider)
Window sashes slide open from both the top and bottom. On a windy day you could open the top sash and ventilate the room in comfort. This design provides you the ability to clean both sashes from inside the home.

Single Hung Window (Vertical Slider)
When the top sash is fixed and the bottom sash slides up for ventilation.

Double Slider Window (Horizontal Slider)
Both slashes slide open horizontally from each end. Both sashes can be lifted out or can tilt in for cleaning.sun.

Single Slider Window (Horizontal Slider)
One sash is fixed and only one sash slides open horizontally for ventilation. Only one sash can tilt in for cleaning.

Fixed Window (Picture Window)
Fixed windows do not open for ventilation and can be combined with multiple fixed or operating windows to create a larger panoramic window.

Awning Window
Hinged at the top, the sash opens from the bottom to the outside for ventilation by turning a crank handle. Awning windows work great when reaching over kitchen sinks to open and for privacy in bathrooms. You can leave open for ventilation even when it is raining.

Casement Window
Hinged on one side, the sash opens from the left or the right to the outside by turning a crank handle, providing maximum ventilation. Casement and Awning style windows also provide the most efficiency against air and noise infiltration because they clamp tight when closed.

Bay Window
The window projects out from the wall with a larger centre panel and angled side panels which can open for ventilation. Factory assembled with new wood head and seat.

Bow Window
The window projects out from the wall with four or more equally sized panels curved in the shape of a bow. Operating sections can be incorporated in any panel for ventilation. Factory assembled with new wood head and seat.

Garden Window
The window projects straight out from the wall with an angled glass roof that can crank open for ventilation. Mostly for plants and is popular in kitchen and dining room windows.

Storm Door
Aluminum extruded frame combined with tempered safety glass and screens for ventilation. Storm doors are installed in front of entry doors to provide added security, ventilation and protection from the elements.

Steel Entry Door
Embossed foam insulated smooth metal door panel with the interior and exterior metal skins separated with a wood or composite style to reduce conduction of heat and cold. Pre-painted with optional decorative glass panels, magnetic weather stripping and ball bearing hinges.

Fibreglass Entry Door
Embossed foam insulated woodgrain panel. Non conductive material is warmer than steel and will not dent or mark as easily. Factory stained with optional cherry, oak or mahogany grains for that natural wood look. Decorative glass is available. Compression weather stripping, ball bearing hinges and standard multi-point lock sets included.

Single Entry Door
Is a door panel with a frame available in 32″, 34″ and 36′ widths.

Double Entry Door
Two door panels with a main operating door closing into the fixed door with astragal bar. The fixed door can be opened by releasing the top and bottom latches on the astragal bar. This feature is to provide a large opening for moving furniture.

Side Lite
A side lite is a narrow framed panel section that is attached to either or both sides of a single or double entry door system. Side-lites are also available with decorative glass to match the entry door.

An additional framed section filled with decorative glass that is fastened to the top of an entry door system. Transoms can be rectangular, round or elliptical in shape.

Swing Patio Door
Similar looking to a double door system with only one side opening and the other side is fixed in place. The operating door panel can be hinged at the side jamb or hinged to the fixed panel in the centre, allowing the operating panel to swing in against the other panel when space is limited. Also comes with a sliding screen for ventilation.

Sliding Patio Door
Full tempered glass panels with metal, wood or vinyl reinforced sashes. One panel will slide to open with a sliding screen for ventilation. Used when more glass area is desired or when there is no room to swing in a door panel.

Lift and Slide Patio Door
Full tempered glass panels with metal, wood or vinyl reinforced sashes. To open, the handle is turned and the one panel will lift and then slide. Also comes with a sliding screen for ventilation.

Folding Patio Door
Full tempered glass panels with metal, wood or vinyl reinforced sashes. Designed for very large wall openings where four or more panels are required. One panel will swing open for regular traffic or all the panels will fold and slide open to one side for entertaining. Retractable screens are required for this design.

The part attached to the fixed panel of door or window which creates a seal for the operating panel to close and lock into.

Brick Mould
The exterior part of a window or door frame that overlaps the wall stud. Approximately a 2″ x 2″ material that the brick or siding butts up against, providing a surface to apply caulking to.

Cam Lock
The device used to lock two sashes together when in the closed position.

A soft and flexible lead material used to hold decorative glass pieces together that are offered in entrance doors.

Capping or Cladding
A protective material made of metal or vinyl that is applied to the exterior surface of a wood product.

A rubber or silicone based product that is applied to exterior joints which prevents air and water from penetrating.

Dead Bolt
Used on entry doors this locking mechanism adds extra security by engaging an extended throw bolt into the door frame.

A silica based product in spacer bars used to manufacture insulating glass units. This product absorbs moisture from the air inside the sealed glass unit, preventing condensation from forming inside.

Door Jamb
The part of a door frame which consists of the sides and head.

Door Slab
The door slab is the actual panel which is fastened to the door frame.

Door Sweep
The door sweep is a weather stripping component that is fastened to the bottom of the door slab, to seal against air and water infiltration.

Dry Glazing
Is a rubberized seal used in place of a butyl or rubber caulk, where extreme heat is a factor.

Egress window or door
A minimum clear opening size as required by local building codes, to allow occupants to escape through the opening in case of a fire.

The result of shaping aluminum or vinyl by forcing the material through a die to produce a length of material formed to a specific shape or profile. The extrusion consists of multiple chambers and internal walls for strength.

Flanker The designation given to a unit that is at either end of a centre unit.

Is a sheet material that protects the joint between a window/door frame and the adjacent construction by preventing water penetration and draining it to the exterior.

Float Glass
Is glass that is formed by a process of floating the material on a bed of molten metal. This produces a high optical quality glass without polishing or grinding.

Full Screen
A screen which covers both or all operating sashes of a window.

Fusion Welded
The process of heating the joints of a pvc window to extreme melting temperatures and bringing the heated joints into contact until they fuse together, creating a permanent bond.

A closed cell continuous strip of material used to create a watertight seal between joints that may be affected by water or air penetration.

Is the process of sealing the glass to the frame or sash.

Glazing Stop
This is a piece of material which holds the glass in place.

Decorative vertical and horizontal bars that are installed between the glass panes to create the appearance divided glass panes.

Half Screen
This is a screen that covers only the operating sash of a single hung or single sliding window.

Is the horizontal top part of the frame of a window or a door.

This is the horizontal structural framing member that is at the top of the rough opening which supports the load of the wall that is above the actual window or door.

Is the component fastened to a door or window sash that allows it to swing opened and closed with ease.

I.G. Unit
An insulating glass package made up of individual panes of glass joined by a spacer bar and hermetically sealed around the complete edge of the unit.

This design feature enables sashes to engage each other when in the closed position.

Jamb Extensions
Are the pieces of wood or vinyl which are fastened to the interior window or door jambs to match the depth of the wall providing a surface to fasten the interior wall casing trim to.

Lift Rail
A handhold integral part of the sash designed for raising, lowering or sliding the window sash.

A unit of glass used in a window or door.

Main Frame
This is the combination of a head, jambs and sill components of a window or door system.

Meeting Rail
Where the vertical or horizontal sections of a pair of sliding sashes that meet when the sashes are in a closed position.

It is the fiberglass material used when making window or door screens.

It is the vertical or horizontal connecting unit between multi-lite windows or doors.

Multi-point Hardware
It is a window or door locking hardware that locks in multiple locations all at once with the operation of only one handle.

Muntin Bar
The term used for a vertical or horizontal bar used to separate glass into multiple lites.

Nailing Fin
An extrusion attached to the window or door frame that is used to secure the unit in place into a rough opening.

Obscure Glass
A glass that is translucent for privacy instead of clear.

Operable sash
It is a window that has a sash that opens for ventilation.

It is the handle that is used to crank open casement and awning windows.

Pivot Bar
It is the metal pin that is attached to the window sash of sliding windows that will allow you to tilt them in for cleaning.

Pull Handle
Is the handle or rail that is built into the sash of a sliding window to enable you to open and close the sash.

It is poly vinyl chloride which is used in extruded vinyl windows.

Retrofit Installation
It is the replacing of product that was not provided at the time of original construction.

It is the exposed part of the window or door jamb extension that is not covered by the casing trim.

Roll Formed
It is a method of fabrication in which light gauge aluminum is run through a machine that bends and forms the metal by using various rollers.

Rough Opening
Is the framed opening in a wall in which the window or door is to be installed.

Safety Glass
It is a strengthened or reinforced glass that is less subject to breakage.

It is the frame around the glass unit that slides or fits into the window frame.

Screen Pull Tab
A pull tab is a small nylon grip that you use to remove the window screen.

Seal Failure
It is when a sealed insulated glass unit begins showing signs of condensation or milky residue in between the panes of glass.

Are wood or plastic wedge shaped pieces used to square the window or door in place during the installation process.

Square Foot
It is the unit of measure for designating an area of one foot by one foot. When calculating in inches you multiply the width x the height divided by 144 = area in square feet.

It is the vertical edge of a door, window or screen.

Is the vertical wood framing member that is used to frame a wall.

Tape Glazing
Is the two sided tape used to secure and seal the glass to the sash.

Tempered Glass
Is a heat treated hardened safety glass that is used in all entry doors and storm doors. Should the glass break it will fall into small pebble like pieces without sharp edges.

Thermal Break
It is the non conductive material that is used to separate two thermally conductive materials, like aluminum.

Thermal Expansion
This is a change created in the dimensions of a material as a direct result of a change in temperature.

Tilt Latch
It is a mechanism that releases the sash and allows it to tilt in for cleaning.

Tilt-In Sash
This is a sash that can be tilted down or swing in to the interior for glass cleaning.

Venting Unit
A window or door unit the opens or operates.

It is the generic term for modified PVC or Poll Vinyl Chloride.

Warm Edge Spacer
It is a non conductive spacer used to make insulated glass units.

Weather Stripping
A material used to form a weather resistant seal around the operating sashes of windows and doors to prevent water and air infiltration.

Weep Holes
Small holes in window and door sills designed to allow water to escape.

Weep Hole Covers
A cover over the weep hole designed to allow the water out and close to prevent insects in.

Wet Glazing
Is a silicone based sealant used to secure and seal the glass to the sash.

Window Frame
It is the fixed component of a window which holds the sash and operating hardware or the window.

Window Style
The description of the way the window looks and operates.

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