Air Infiltration or AI as important as R value..

[rebar]

Correct me if I'm wrong that the U value number is a reduction of R value mainly because of AI, so my opinion is that R value is almost meaningless if you have much AI at all..

Ive come to that conclusion after being a member of a "green" netzero online community who publishes the performance of different homes they showcase.. One of the homes was built with 6" walls with blown in insulation and was said to perform to passive house standards because of the builders attention to minimizing AI..

Which door and window brand the builder installed was not mentioned, but I knew at that time that anything more than a R30 wall and R60 ceiling was chasing diminishing returns.. And after learning that passive solar doesn't work in my area and is a wash in others, tells me that minimizing the biggest lose of heat (windows) and minimizing AI was the direction or goal I wanted to achieve with my new home..

But what company has reliable AI numbers? I'm mainly asking about my big garage door, but the entire package will decide how efficient my new home will be.

Thanks..

[Windows on Washington]

Nuance to it.

U-Factor is the inverse or R-Value so a lower U-Factor is ideal. You are correct thought...a window with a mediocre U-Factor and a very good Air Infiltration rating will "dynamically" (i.e. as an installed product in a home) out perform the window with a slightly lower U-Factor but higher Air Infiltration rating.

The analogy that most folks get is to put your back to your freezer door...it's cool but not uncomfortable. Now, crack the freezer door open...it's very cold. Kind of like that.

[rebar]

Thanks Washington. You confirmed my opinion.

How would you suggest I shop for doors and windows with the lowest infiltration numbers?

Do manufactures usually list AI numbers, or will I find U values?

[Windows on Washington]

Some list...some you have to ask.

[HomeSealed]

+1. To be clear, AI does not have any impact on R value or U value, however you are correct in the premise that those thermal ratings are of limited value without considering AI in the overall performance of a home.

As far as shopping for windows with good AI ratings, it's both tricky and stupidly obvious at the same time. Many companies will attempt to hide or downplay those ratings, and some will even go as far as manipulating them by quoting picture window numbers or ridiculously sized units that do not correspond to the certified rating for the product.

The simple part is knowing that generally speaking, companies that have high performing windows promote those ratings prominently in their brochures etc. Those that don't, do not... This is a pretty general rule that has some exceptions but gives you a good starting point.