Sorry for that UT A&M article, its a tough read but in the conclusion, does refer to energy loads. This one Iam linking to now is more appropriate, informative and easy to read. Author John Straube needs no introduction in the building science community. Its a good article for anyone building a home that explores air infiltration impacts on homes other than energy use. On infiltration's impacts to energy use related to HVAC, he agrees with wickipedia too: 1/3. Verifying Airtightness with blower doors saves energy, prevents rot and helps ensure we have CONTROL over mechanical ventilation. Manual J is an amazing tool. Its incredible how accurate it can be in the hands of a skilled user. I dont think Manual J or other energy software results are being used appropriately when extremely detailed outputs from limited samples involving many variables with built in fudge factors are being used to talk the community into building below energy code minimums. Here is a link that might be useful: Building Science.com link; Air Leaks--How they rot homes and waste money This post was edited by Brian_Knight on Tue, Feb 5, 13 at 22:19

We have Pellas with blinds between the panes. I know that part of our problem has been in the customer service part of the deal but I do have to tell you that we have had a 2 1/2 year nightmare with Pella. Our windows arrived with scratches and nics on the hinged glass panels that swing out to access the blinds. Nearly all of our blinds ( we have 33) have had to be replaced 3 times and some even 4 and 5 times. The windows also have suction cup marks on the outside sash that show up when the windows get condensation or if there is a bright light shining through. Our first set of windows was declared defective by the service tech because of scratches and a residue that would not come off and spiderweb like debris in the glass. The second set of windows arrived in the same condition, one even stress fractured a year later. We had to fight to get 12 sashes and hinged glass panels replaced for a 3rd time. They really should ALL be replaced. This was all done with the expense of an attorney. The blinds between the windows seem like a nice feature but they aren't the best blinds, they are hard to access, they are light filtering not room darkening, and it gives you 4 panes of glass which need to be cleaned rather than 2. Cleaning is difficult and more often than not when the hinged glass panel door is opened and then closed again it causes the blinds not to function properly. I could tell you a lot more about Pella but in a nutshell we have spent 2 1/2 years and a lot of money trying to get windows that live up to the price we paid for them. They have failed us in service,in quality, and in customer satisfaction. The service manager even told me that he didn't think Pella could provide us with clear glass! What does that tell you! I am sure other people have horror stories from other window manufacturers too, but I cannot in good conscience ever recommend Pella to anyone and if I have the chance to discourage them from purchasing them I certainly will. They are NOT viewed to be the best, especially when your view has scratches and smeary glass, suction cup marks showing and blinds that are crooked.

The Alpen windows looked better than I thought a fiberglass window would look like installed in a home. I haven't found a local rep for the Thermotech windows from Canada. I'll go look at a place with H Windows tomorrow. It's pretty hard to compare performance on windows. And light transmitance seems pretty low on a number of brands.

Sealing a home should be an comprehensive process. If you seal a home and do not allow for fresh air mixing/transfer, you can wind up with a 'sick' house. One that will not exhaust stale air/odors and cannot fully utilize the bath/kitchen vent fans. That means a system for air transfer needs to be developed utilizing air mixing and heat transfer equipment with the heating/cooling systems. That is a job for the pros. Doing things that maximize natural forces, like a ridge vent with proper soffit vent area will use no energy other than nature. Hot air rises. Having the vent at the ridge and the fresh air intake for an attic at the lowest point means nature causes the air in the attic space to be continually replaced, no matter what the out side temperature. Insulate the attic(using the sealing ideas already provided above) and you have a 'Forget it' attic. I did add blow-in insulation to our attic---12" worth. Our house was built in 1965. Subsequent owners have added insulated siding and add on storm windows. Those two things have almost completely the major leak points around windows. The windows are the original 1965 wooden sash double hung styles units. With the added storms, they function almost as well as double pane modern types. When we change them, it will be for the ease of use/cleaning, not for energy savings. The advice about rim joist insulation is spot on. Weatherstripping exterior doors offers a lot of options. The following video is pretty good. Adding a storm door can also help sealing.