I am trying to compare the Pella windows sold by the Pella sales person with the Pella windows sold at the big box stores (Lowe's, Home Depot). I have found a spec sheet with this information for Lowe's. I found a spec sheet for Pella Pella but it doesn't have a U-value.

Example 1: it brags about the U-factor and offers a footnote that says, "Based on comparing product quotes and published STC/OITC and U-Factor ratings of leading national wood window and patio door brands."

Example 2: No mention.

For the 250 series I found a U value at Lowes of 0.27 here (click on "specifications").

1 Answer 1


As with most items, there are good, better and best. With Pelli, you can break that down into another hundred parts or so.


In the construction industry, most items (locks, carpet, windows, roofing, etc.) are divided into “design grade” and “spec grade”.

Design Grade is the top grade and used by architects and contractors for top performance. Here clients are looking for the best long term performance. Here’s a sample of what architects select from: https://content.pella.com/cs/groups/public/documents/document/mhat/mdy2/~edisp/p-066812.pdf?_ga=2.190888361.2053217315.1575606363-1340307589.1575606363

Spec Grade is the lower grade and is usually used by spec builders, box stores, etc. These products are often chosen based on lowest cost. (If a manufacturer can “save a buck” to get the sale, they’ll do it at the expense of performance.) So a box store often has one low cost (and low performance) for home owners to choose.


The “U value” of windows depends on 1) quality of frame, 2) number of panes of glass, 3) argon gas, 4) low E coatings, 5) air space between panes, etc.

So, in your “Example 1” where they show the window has a U-value of 0.27 it’s because the are using their lowest quality (and least expensive) frame and glazing.

However, in your “Example 2” they do not list a U-value because there are a gazillion glazing and frame options. (Thank you Pella for making it so complicated.) Here’s a sample of some U-values (appears to go down to 0.15) for a couple different style of Pella windows: www.pella.com/professional/adm/Clad-Wood/Pella-ArchtctSrsTrad_Awning.pdf

Take your pick, but it looks like you can get something significantly better than the “Spec” windows at a box store...if you’re willing to pay for it.

Fortunately, Pella is a high service manufacturer, so call them and they’ll walk you through the performance of the options. Then call a glazing company to get a bid.

  • Ha. I've been trying to get hold of the salesman for two weeks with follow-up questions. // Thanks for the first link. (The second one doesn't work.) I see some very low U numbers in your link. This is encouraging. Dec 6, 2019 at 7:29

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