Post date: Oct 18, 2014 3:22:19 PM
I’m back to considering windows. Not that the house is ready for windows, but they are such a big part of the budget, and affect my future comfort so much that I am obsessing over them.
I discovered that windows have something in common with lighting fixtures - there is an enormous amount of variation. Of course with lighting fixtures you can easily see the variants. With windows most of the variables are hidden. And the manufacturers seem to want to keep it that way.
Being a techie, I researched the variables in window making. Here is what I found.
Windows are made of frames and glazing and hardware.
The frames can be made of several materials, alone or in combination:
Each of these has some advantages and some disadvantages.
Wood looks nice, but needs maintenance if it is not to deteriorate in the beating it gets from the sun and rain. It also swells and contracts with changes in moisture content, making it hard to seal. So wood window frames are often clad on the outside with vinyl or aluminum for protection.
Aluminum almost doesn't deteriorate and can be anodized to a range of colors, meaning it does not have to be painted. But aluminum is a very good conductor of heat, and leaking the heat out of your house through the window frame is not a good idea. Steel was once a material of choice for casement windows, but it rusts, in addition to conducting heat.
Vinyl frames were poorly made when they were introduced, giving the material a bad reputation. But welded corners and foam-filled cores make this a good material. It can be colored, but ultraviolet sunlight can damage the plastic if it is not protected. Vinyl is not particularly strong, so the frames tend to be thicker.
Fiberglass is strong, stable, and paintable. The manufacturing process is more expensive than the alternatives. The frames can be narrow.
Composites of wood waste and plastic binders, related to particleboard and composite decking material, is a recent addition. The wood provides fibrous strength while the plastic protects the fibers and simplifies manufacture of complex shapes.
Insulating windows use double (or more) glazing to reduce heat flow.
While many of us can understand the variations in frames, the possibilities in glazing are less obvious. Glazing consists of the following elements:
The glass itself is generally invisible. However the glass can be tinted. There is also ‘self-cleaning’ glass, used for the outer pane, called ‘SolarClean’, primarily used on photovoltaic panels but also available for windows.
The spacers between the two (or more) panes of glass must keep moisture out. Typically made of aluminum - but that metal conducts heat. Newer spacers are made of insulating foam and sealed on the outside. Failure of the spacer is the biggest reason for replacement of insulating windows.
The gas between the panes of an insulating window is often argon, because it conducts heat less than air. Krypton is even better but costs more. A vacuum between the panes is ideal, but the seal around the edge has not been perfected.
Coatings on the glass reduce the transmission or radiation of certain wavelengths of light. Low-Emissivity, or Low-E glass coats one internal surface to reflect the heat rays. The low-e coating lowers the overall heat conductivity of the window, and different types of low-e coatings have been designed to allow for high solar gain, moderate solar gain, or low solar gain. This can block 84% of ultraviolet rays (per Pella). There are two different types of low-e coatings: passive low-e coatings and solar control low-e coatings. Solar control coatings are used in warm climates and are sputtered onto the glass. Passive low-E coatings are fused into the surface of hot glass and are also called ‘hard’ coatings and are used for heating-dominated climates, like Taos.
An additional internal film improves insulation (per Eastman) to R-6 or more with more film chambers, while changing Solar Heat Gain Coefficient (SHGC) over standard double-pane glazing. Alpen calls this suspended film and claims that it is easier to tune the window performance to the orientation and climate. Triple-pane windows can achieve the same results with more bulk and weight than film.
Hardware consists of weatherstripping, hinges and/or springs, handles, cranks (for casements), latches, shades, and screens. This also determines which way the window will open - or not open. There is quite a variety:
And when an opening casement window extends to the floor it is called - you guessed it - a ‘door’.
I don’t have much to say here, yet…
If money were no object and any manufacturer had all my ideals available in a real product, I would choose the following combination:
Now the challenge is to find all this in a window that I can afford.