Insulation is typically measured in "R" values, where higher numbers indicated better performance. In windows, this measurement applies only to the frame; the glass is measured in "U" values, where lower numbers are better.
You cannot see with the naked eye how well a window is insulated. You must use a thermo-cam.
Window materials are graded according to their insulating performance.
Slider windows may be used when a window opening is wider than it is tall and are often used when a homeowner wants the look of a casement window. Inexpensive slider windows do not seal up very well at all. They may qualify as egress windows if large enough. It is very important to install these correctly.
Awning windows are most often installed for people who have had them before. They carry a mid-range price tag because of their hardware. Awning windows are a good window to use if you like to have a window you can leave open when it rains. However, these are not a great window for ventilation.
Vinyl windows normally carry a lifetime warranty, but there are two types:
Vinyl windows will not rot and have very little to no maintenance. They're available in a variety of different finishes to give the appearance of wood or different colors, so you don’t have to paint or stain, ever. And unlike with wood windows, you won't have to worry about insects with vinyl windows.
There are two forms of insulation for vinyl windows.
The amount of vinyl used can vary greatly between brands and models of vinyl windows. Inexpensive windows will have the least vinyl. This becomes increasingly important in larger windows as the weight of the glass may cause the vinyl to flex. In larger windows or doors, good manufactures will reinforce the vinyl with fiberglass to keep the frame from flexing.
Full frame replacement windows are more expensive, as the old window is entirely removed.
Options on the outside:
Some installers will install a pocket window in this opening, but they are then relying entirely on caulk to seal up the gap left from the install. Caulk fails over time. Some caulk is paintable but not all.
A bay window has only three sides; a bow window may have many more. Bay windows feature 45º flankers and project farthest from the side of the house, which can be supported from above or below. These are typically the most expensive window option.
Picture windows are becoming more popular because of people with allergies and asthma.
They're the least expensive window and cannot be opened for ventilation.
Casement windows are the most expensive option because of their hardware. Most people either love or hate these windows. There is no in-between. These windows provide good ventilation without even opening another window. A big negative is, when the windows is open and it is raining, the window can act like a scoop and let in a lot of rain.
It's very important to make sure of good quality, as these windows are very prone to damage from winds. The hardware must support all the weight when open. Multi-point locks are best, and, when locked, these are the best window for keeping out drafts.
The screens are on the inside because of how the window opens. This can cause problems with insects being caught between the glass and screen when you close the window. Screens can be damaged from pets and kids but are less susceptible to weather damage.
Casement windows are often used in bathrooms for ventilation and for egress windows in basements or bedrooms.
Basement windows are best replaced with slider windows.
In double hung windows, both sashes move. Accordingly, these are a little more expensive than single hung windows but still less expensive than casement windows.
Double hung windows provide their best ventilation when you have windows on opposite sides of the house that can be opened at same time.
Opening the bottom sash only (most common)
Opening top and bottom sash
Opening the top only
Tilt-in windows are very easy to clean.
These windows are installed by taking out the old operable sashes and leave the existing window jambs. The opening that is left is the pocket (hence the name). The plus side of these windows is that they are very less expensive. They are also able to be installed quickly and without making much of a mess.
Insulation values can be good in wood windows, but it depends on what type of wood is used.
Old windows used a very dense hardwood. When painted or varnished, this made for a window that would be able to hold up to the UV and weather over time.
Some newer windows use “green” wood. This is from trees that are planted and genetically engineered to grow fast and then harvested. This is a great idea to save forests, but the downside is that the wood is generally softer and more porous. If not sealed properly, this wood is very prone to water absorption. You can order some windows prefinished from the factory, but there are others that you will have to stain and varnish yourself.
Most wood windows have somewhere in their warranty that you must do maintenance yearly on the windows, including scraping to remove old paint and varnish that has broken down from the UV and re-applying paint or varnish.
Homeowners asked for the low-maintenance wood windows, so manufacturers made a color clad window that is a wood window with some type of covering on the outside wood. There has been a huge problem with this because they are relying on caulking to keep water from getting between the coating and the wood. All caulk fails over time. When this happens, the wood rots, and the only way that you know is one day you open the window and the glass falls out the bottom. You might get lucky enough to have a casement window and the opener pulls out before you can get the window open. These are a very poor design.
Wood windows typically carry a limited warranty.
Metal windows are great windows that last a very long time and hold up well to the abuse of opening and closing. They're very low maintenance.
Still, they're not without their downsides. Metal windows are not good at all when it comes to insulation, are prone to freezing shut, and are only available in a limited selection of colors.