As much as thirty percent of energy loss happens here.
Remember, heat seeks cold. Heat looks for cold! Heat then moves toward cold!
In a finished house, assuming everything is in place (including insulation) the energy loss (meaning thermal movement - heat toward cold) breaks down more or less like this:
> 30% of loss happens through the attic ceiling.
> 30% of loss happens through walls.
>30% of loss happens through windows and doors.
>10% of loss happens through exterior wall or uninsulated ceiling penetrations like switches, receptacles and lights.
Obviously those percentages change if walls or ceilings are not adequately insulated, or there are really lousy windows and doors. But overall those percentages are a pretty good rule of thumb.
These thermal images are examples of a door and window IN NEW CONSTRUCTION!
Wow. How would anyone know without seeing such an example with a thermal camera?
Not only is the weather stripping poorly placed around the door, but the insulation as well.
And not only is the window leaking (this is a basement fire escape window) but the insulation is poorly placed here too. The temperature outdoors was about 50F at this time, so think what these images would look like on a really hot or cold day.
Do you not think that all over a house this would not, could not, have a dramatic effect?
My recommendation: when you buy new construction find out what kind of windows and doors will be installed. Their quality, performance, U-factor and weather stripping. Will they be Energy Star, or some other standard, quality? Who will the subcontractors be as regards insulation and window and door installation? Find out what they do - for example, will they foam around windows and doors in addition to insulation? Check out their reputations, licensing, how carefully they treat the materials, and how many will be involved with the installation. All these things add up! Remember the 5% rule - if only 5% of the insulation in a room is poorly placed, or missing, it will affect the R-value performance of that space by 50%! (Click on the orange link to see my post on this subject) And if windows and doors all over the house are poorly installed you will be in for a lifetime of energy loss. Be proactive!