We demand a lot from our windows. In the warmer southern climates, we want them to keep the cold air in during the dead of summer, but we want to open them to let in fresh air on milder, less humid days. We want them to let light in, but we don't want them to radiate the sun's heat inside and warm things up. Windows can be one of the greatest sources of heat infiltration and air loss, so what do you do about them? One option is to replace them, but that can get awfully expensive. If you can't afford to replace them, or if you're not going to be in the house long enough to justify the investment, seal them up as best as you can to minimize air leaks, and do what you can to minimize the radiant effects of the sun.
Regarding doors, you again have the option to replace or to improve the air sealing qualities. Some of the same ideas for windows apply to doors, so you can adapt for the type of opening.
Exterior Doors
I won't spend too much time on this subject, as most of this should be pretty straightforward. If you've got an old, leaky door, see about replacing it. The major home improvement stores have pre-hung doors with decent weather sealing, and when installed right, the investment will pay for itself in a relatively short time. Have (or want) something fancy? Does your front door make a statement about you? Get ready to drop some bucks. Top-of-the-line entry doors at your home improvement stores can run several thousand dollars. Go to a custom window and door place and get ready to drop over ten grand for a high-end custom fiberglass door.
Don't want or need to replace the door? Then weatherstrip it. Don't get that wimpy, worthless, stick-on foam crapola they sell in the weatherstripping section at the local hardware store. To do it right, you need vinyl, rubber, silicone, or (my preference) copper/bronze weatherstripping. I haven't researched who supplies this stuff, but it is out there to be had. My current doors all have the copper stuff around them, and with a little bending, I was able to re-establish a good seal around my doors. If you have this type of weatherstripping on your door, spend the time to do this to reduce air leakage around the door frame while it is closed. It's pretty easy: if you can see light through the seal, you need to work on it. If not, then it is probably sealed up pretty well. You can also sometimes feel air moving around the door casing; if that's the case, fix it! Have leaks around your locksets? Look at getting foam inserts to stop the airflow.
I'll touch more on this briefly in the sealing section, as reducing airflow definitely falls under that category.
Windows
Windows can account for up to 30% of all airflow from conditioned space to outside (or vice versa), and they account for a huge percentage of radiant heat gain in a house. So how do you fix those problems?
The first, and most expensive, option is to replace your windows with new, low-E, high efficiency windows. They have made some major advances in window performance in recent years: double- and triple-pane windows (great for energy efficiency as well as noise reduction); low-e coatings; inert gas fillings; frames and sashes that vastly reduce, if not eliminate, heat transfer through those parts of the window; and more. The problem is replacement windows are generally extremely expensive. My parents recently invested over $18,000 in replacement windows for their house (and I consider myself extremely fortunate to have inhereted them when I bought that house - they're awesome and block out so much noise). Out of curiosity, I invited a salesman out from Gulf Coast Windows to give me estimates on replacing the 26 windows in my old Katy house. They've got an awesome product, awesome warranty, and the service and installation stuff looked good, too. But they're proud of it. The total: over $33,000!
Yeah, it took me a few hours to come off of life support after hearing that. And that was the first of two shocks in three days, as you'll see when you read my section on air conditioning equipment. Anyway, after weighing the benefits versus the acquisition costs, the payback on that investment is over 15 years (closer to 20), and I wasn't planning on staying in that house that long. Needless to say, that idea was axed real quick! If you're going to be in a house for a long period of time, and the investment payback isn't the only reason you're looking at them, replacement windows might be for you, but they weren't for me at that particular time.
But I still had the problem of air leaks and radiant transfer. I didn't get around to tackling the leakage problem before I had to sell the house after my divorce, but I did tackle and, to a big degree, solved the radiant problem. How did I do it? With window film. I went shopping and found that the stuff I really wanted - 3M's ScotchTint Sun Control film (it is now called just Sun Control film) - was, as far as I could tell, only available to professional installers. So I found some other stuff that isn't quite as good as the 3M stuff, but it is readily available and relatively affordable.
I chose Gila's Platinum Heat Control film. The stuff is available at the Blue Store and the Orange Store, and probably elsewhere, and it isn't terribly expensive. I used the 3' x 15' rolls, and it ran between $36 and $38 per roll, depending on the store I bought it from. Gila claims that their Platinum film blocks up to 70% of the radiant heat and 99% of UV rays that come through windows while still letting around 70% of the visible light through. It did darken the rooms some, and it did change the color of the light slightly (it has a somewhat grayish hue to it), but only slightly - not like you think of darkening a room with "tint." Outside, the windows definitely have a more reflective surface to them now (during daylight, it looks to have a goldish tint to it), but it didn't alter the look of the windows significantly, and you can still see through them from the outside. At night from the inside, you do get somewhat of a mirrored effect, but you can still see outside if you have outdoor ambient light. 3M's product, on the other hand, claimed over 90% radiance blockage, and it is almost clear, allowing around 90% of the visible light through. But you pay for it, both in product and installation costs. That's why I chose the Gila film, because it is affordable and I could do it myself.
I used 8 rolls of it on the Katy house, and I covered all upstairs windows (except the small north-facing window in one of the upstairs bathrooms) and all of the south- and west-facing windows downstairs. How well did it work? Well, I can say for sure my upstairs air conditioner actually kept up during the heat of the hottest days, where it didn't before. I couldn't be certain exactly how much less it is running, because my thermostats didn't have a total runtime counter on it, but I know it definitely ran less, kept up better with the load, and made the upstairs more comfortable. Another telltale sign: where the sun would shine through the window and onto some surface (floor, countertop, etc.), before the film you could feel the heat gain where the light was shining. Where there was light, there was warmth - warmth that the air conditioner ultimately had to cycle out of the house. With the film installed, there was virtually no surface temperature change between the areas taking direct sunlight and areas that were not. In short, the film reduced the heat load placed on my air conditioners.
So in short, if you have older windows that take a lot of direct sunlight - and you can't afford or it doesn't make financial sense to replace them - get some of this film (or some like it) and slap it up there. You'll notice a difference in improved comfort levels, reduced air conditioning load, and lower electricity bills!
As a side note in the interest of completeness, I should mention that window shading is also a viable alternative. Interior blinds can help reduce the radiant transfer, but they will still allow the air between the windows and the blinds to heat up. Another option is awnings, covered patios and the like. Shading the window and preventing direct sunlight while still allowing light to come through the window could be a viable option. Trees and possibly shrubbery can accomplish the same goal, but it does take time to grow them.
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