Double-Pane Window Condensation Issues
Condensation is the accumulation of liquid water on relatively cold surfaces.
Almost all air contains water vapor, the gas phase of water composed of tiny water droplets. The molecules in warm air are far apart from one another and allow the containment of a relatively large quantity of water vapor. As air cools, its molecules get closer together and squeeze the tiny vapor droplets closer together, as well. A critical temperature, known as the dew point, exists where these water droplets will be forced so close together that they merge into visible liquid in a process called condensation.
Double-pane windows have a layer of gas (usually argon or air) trapped between two panes of glass that acts as insulation to reduce heat loss through the window. Other types of gas used in this space have various effects on heat gain or loss through the window. Some double-pane windows also have a thin film installed between panes that separates the space between the panes into two spaces, further reducing heat loss and heat gain through the double-pane window. If multiple-pane windows appear misty or foggy, it means that the seal protecting the double-pane window assembly has failed.
Silica Desiccant Use In Double-Pane Windows
A desiccant is an absorbent material designed to maintain dryness in the space it protects. In a double-pane window, silica pellets inside the aluminum perimeter strip absorb moisture from any incoming air that enters the space between the panes. If not for the silica desiccant, any moisture in the space between the panes would condense on the glass as the glass cools below the dew point temperature.
Silica gel has an immense surface area, approximately 7,200 square feet per gram, which allows it to absorb large amounts of water vapor. As the sealant protecting this space fails over time, increasing amounts of moisture-containing air will enter the space between the panes, and the silica pellets will eventually become saturated and will no longer be able to prevent condensation from forming. A double-pane window that appears foggy or that has visible condensation has failed and needs to be repaired or replaced.
Why Double-Pane Windows Fail: Solar (Thermal) Pumping
Although double-pane windows appear to be stable, they actually experience a daily cycle of expansion and contraction caused by thermal pumping. Sunlight heats the airspace between the panes and causes the gas there to heat up and expand, pressurizing the space between the panes. At night, the double-pane window cools and the space between the panes contracts. This motion acts like the bellows of a forge and is called thermal pumping.
Over time, the constant pressure fluctuations caused by thermal pumping will stress the seal. Eventually, the seal will develop small fractures that will slowly grow in size, allowing increasing amounts of infiltration and ex filtration of air from the space between the panes.
Failure Factors in Double-Pane Windows
Double-pane windows on the sunny side of a home will experience larger temperature swings, resulting in greater amounts of thermal pumping, seal stress and failure rates.
Vinyl double-pane window frames have a higher coefficient of expansion resulting in greater long-term stress on the double-pane assembly, and a higher failure rate. Double-pane windows also experience batch failure, which describes production runs of windows, especially vinyl windows, that are defective, meaning that the double-pane assemblies have been manufactured with seals that have small defects that will cause the window to fail prematurely.
The Nature of Damage to Double-Pane Windows
If it’s allowed to continue, double-pane window condensation will inevitably lead to irreversible physical window damage. This damage can appear in the following two ways:
- riverbedding. Condensed vapor between the glass panes will form droplets that run down the length of the window. Water that descends in this fashion has the tendency to follow narrow paths and carve grooves into the glass surface. These grooves are formed in a process similar to canyon formation.
- silica haze. Once the silica gel has been saturated, it will be eroded by passing air currents and accumulate as white “snowflakes” on the window surface. It is believed that if this damage is present, the window must be replaced.
Detecting Failure in Double-Pane Windows
Double-pane window condensation is not always visible. If the failure is recent, a failed double-pane window may not be obvious, since condensation doesn’t usually form until the window is heated by direct sunlight. Double-pane windows in the shade may show no evidence of failure, so inspectors should disclaim responsibility for discovering failed double-pane windows.
Thermal Imaging as a Detection Tool
Under the right conditions, it’s possible to use an infrared (IR) camera to detect failed double-pane windows. IR cameras are designed to record differences in temperature.
Recommendations for Failed Double-Pane Windows
According to industry experts, the glazing assembly can be replaced approximately 75% of the time. Occasionally, the sashes must be replaced, and only about 5% of those cases require that the entire window be replaced.
There are companies that claim to be able to repair misty double-pane windows through a process known as “defogging.”
This repair method proceeds in the following order:
- A hole is drilled into the window, usually from the outside, and a cleaning solution is sprayed into the air chamber.
- The solution and any other moisture are sucked out through a vacuum.
- A defogger device is permanently inserted into the hole that will allow the release of moisture during thermal pumping.
There is currently a debate as to whether this process is a suitable repair for windows that have failed, or if it merely removes the symptom of this failure. Condensation appears between double-paned windows when the window is compromised, and removal of this water will not fix the seal itself. A window “repaired” in this manner, although absent of condensation, might not provide any additional insulation. This method is still fairly new and opinions about its effectiveness range widely. Regardless, “defogging” certainly allows for cosmetic improvement, which is of some value to homeowners. It may also reduce the potential for damage caused by condensation in the form of mold or rot. Some skepticism exists about the effectiveness and cost effectiveness of this method of repair.
Condensation in double-pane windows indicates that the glazing assembly has failed and needs repair or replacement. Visible condensation can damage glazing and is the main indication of sealant failure.
Other Double-Pane Window Information
How to Install Attic Insulation
Attic Insulation installed correctly, can help cut your energy costs.
According to the EnergyStar™ Program, heating and cooling costs can be slashed by up to 20% per year by properly sealing and insulating the home.
Adding Insulation in your attic should be a top priority for preventing heat loss because as heat rises, a critical amount of heat loss from the living areas of the home occurs through an unfinished attic. During the summer months, heat trapped in the attic can reduce a home’s ability to keep cool, forcing occupants to further tax the home’s cooling system.
The aim should be to insulate the living space of the house while allowing the roof to remain the same temperature as the outside. This prevents cold outside air from traveling through the attic and into the living area of the home. In order to accomplish this, an adequate venting system must be in place to vent the roof by allowing air flow to enter through soffit-intake vents and out through ridge vents, gable vents or louver vents in the attic.
If there is currently a floor in the attic, it will be necessary to pull up pieces of the floor to install the insulation. In this case, it will be easier to use a blower and loose-fill insulation to effectively fill the spaces between the joists. If you choose to go with blown-in insulation, you can usually get free use of a blower when you purchase a certain amount of insulation.
When installing fiberglass insulation in the attic, make sure that you wear personal protective equipment, including a hat, gloves, and a face mask, as stray fiberglass material can be inhaled and cause irritation to the lungs, eyes and exposed skin.
Before you begin actually installing the insulation, there is some important preparation involved in order to ensure that the insulation is applied properly in your attic to prevent hazards and to achieve maximum effectiveness.
1: Install Roof Baffles in The Attic
In order to maintain the free flow of outside air, it is recommended that polystyrene or plastic roof baffles are installed where the joists meet the rafters. These can be stapled into place.
2: Place Baffles Around Electrical Fixtures in The Attic
Next, place baffles around any electrical fixtures (lights, receptacles, etc.), since these may become hot while in use. Hold the baffles in place by cross-sectioning the rafters with 2x4s placed at a 3-inch clearance around the fixture. Cut the polystyrene board to fit around the fixture and inside the wood square you have just created.
3: Install a Vapor Barrier in The Attic
If you are installing insulation with a vapor barrier, make sure it faces the interior of the house. Another option for a vapor barrier is to take sheets of plastic and lay them between the ceiling joists. Then, using a staple gun, tack them to the sides of the joists.
4: Applying the Insulation in The Attic
Begin by cutting long strips of fiberglass to measure, and lay them in between the joists. Do not bunch or compress the material; this will reduce the insulative effect.
If you are not planning to put in an attic floor, a second layer of insulation may be laid at 90º to the first layer. Do not lay in a second moisture barrier, as moisture could potentially be trapped between the two layers. This second layer of insulation will make it easier to obtain the recommended R-value. In colder climates, an R-value of 49 is recommended for adequate attic insulation. In warmer climates, an R-value of 30 is recommended. Fiberglass insulation has an R-value of rough
ly 3 per inch of thickness; cellulose has an R-value of roughly 4 per inch, but it doesn’t retain its R-value rating as well as fiberglass.
If an attic floor is in place, it will be easier to use a blower to insert cellulose insulation into the spaces. The best way to achieve this is to carefully select pieces of the floor and remove them in such a manner that you will have access to all of the spaces in between the joists. Run the blower hose up into the attic. A helper may be needed to control the blower. Blow the insulation into the spaces between the joists, taking care not to blow insulation near electrical fixtures. Replace any flooring pieces that were removed.
Loose-fill insulation, either fiberglass or cellulose, is also a good option in cases where there is no attic floor. In such circumstances, you won’t need a blower, and can simply place the insulation between the joists by hand. You may also wish to even out the spread with a notched leveler.
When inspecting an attic, ensuring that there is a free flow of outside air from the soffits to the roof vents is key to a well-functioning insulation system. The lack of adequate ventilation in insulated attics is a common defect. When inspecting the attic, look behind the baffles to see if there is any misplaced insulation obstructing the natural air flow, and check the roof vents to make sure that outside air is exhausting properly. Check for a moisture barrier under the insulation. Also, look for spots where the insulation is compacted; it may need to be fluffed out. In the case of loose-fill insulation, check for any thinly spread areas that may need topping up. Finally, look for dirty spots in the insulation where incoming air is admitting dust into the material.
Radiant Heating Systems
Radiant Heating Systems for Floors and Walls
Radiant heating systems directly heat the floor or panels in the wall or ceiling of a house, rather than heating the air, as do forced-air
heating systems. The radiant heating technique can be likened to standing in full sun on a chilly day, or feeling the warmth of a distant bonfire even though the air is cold. Despite their name, radiant heating systems also depend on convection — the natural circulation of heat within a room — caused by heat rising from the floor.
Radiant heating has been used since ancient times, perhaps as far back as 4000 BC in Mongolia. The ancient Romans, too, made use of a type of radiant heating known as a hypocaust to heat their houses and public baths. Recent decades have seen more mainstream use of radiant heating in Europe, although it is finally gaining popularity in the United States, especially in new-home construction, where installation of radiant heating is more economical.
Radiant heating systems use one of two heating mediums, each of which is described below:
- water (hydronic) radiant heat: This system uses hot water carried by tubing, arranged in a grid, to heat the home.
- electric radiant floors: This system uses electricity carried by cables or floor mats to heat the home.
An installation of a radiant heating system in a floor is either wet or dry (not to be confused with the aforementioned distinctions), and the decision to use one or the other is largely based on whether the system will be installed in new or existing construction. These two methods are briefly summarized as follows:
- In a wet installation, the heating panels are installed on the floor, and a thin layer of concrete or gypsum is spread over the installation, sandwiching the cables or tubing between two layers of flooring or concrete. This installation is ideal in new-home construction, where a concrete slab, which has high thermal mass, is used to build the ground floor.
- Radiant floor dry installations are relatively new strategies in which the cables or tubing run in an air space beneath the floor. Tubing is often sandwiched between layers of plywood or beneath the sub-floor. Dry heating is more common in retrofits and when the floors in new homes are not poured concrete.
Advantages of Radiant Heating
- efficiency. Radiant heating systems use less energy than convective heating systems where the same fuel is being used. This is due to a number of reasons:
- The thermostat can be set to a lower temperature and still afford the same comfort. Rooms heated by radiance are typically heated uniformly from floor and ceiling, in contrast with forced-air systems, which leave the floors cold. Studies conducted by the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) indicate that people can be as comfortable at temperatures 6 to 8 degrees lower with radiant heating than with convective heating that uses air as the primary heat-transfer medium.
- They require no ducts or pipes, which account for heat losses in other systems.
- There is less heat loss through windows because air is not being blown.
- Radiant heaters can be zoned so that energy is only used to heat individual rooms. You can thus more easily direct heat to areas that are more trafficked or chillier, while directing heat away from rooms that see little use.
- Radiant heating systems, unlike forced-air systems, pose little threat of spreading dust, pollen and germs.
- flexible fuel choices. Hydronic systems can be heated with a wide variety of energy sources, such as solar water heaters or gas, wood or oil-fired boilers.
- unobtrusive. Radiant heating systems are not visible in the occupied space, which saves floor space and allows for more decorative freedom.
- quiet and clean. Radiant heating systems are quiet, clean and require little or no maintenance. An oil-fired heating boiler, on the other hand, requires annual maintenance.
- Radiant heaters take a long time to cool. This can be beneficial in several ways:
- The heater can be run at night during off-peak hours when electricity rates are cheaper. It can then be turned off, yet still radiate heat, during peak hours.
- As it takes a long time for radiant heaters to cool down, they will continue to provide heat for hours into a blackout.
Disadvantages of Radiant Heating
- Additional under-slab insulation is required for radiant heating systems mounted on the ceiling.
- limited choice of floor covering. Carpet, due to its properties as a thermal insulator, reduces efficiency of in-floor systems. Wood, too, may not be a good choice because of its tendency to crack or shrink when heated. If wood must be used, it is best to use wood with a low moisture level to avoid shrinking and gaps.
- potentially high utility costs. In some areas, electricity is the most expensive way to provide heat.
- high up-front cost. Due to their complex installation, up-front costs can be prohibitive.
- long warm-up period. Electric radiant heating systems heat up faster than liquid systems, although both take longer than conventional forced-air systems.
- They can only be used to heat. Separate radiant heating systems are required to provide cooling, air cleaning and ventilation. A forced-air system, by contrast, can do all of these things.
- Maintenance and repair of pipes may be difficult due to their lack of accessibility.
FYI, radiant heating is an attractive alternative to conventional heating systems, although neither system is perfect.