Go Back  DoItYourself.com Community Forums > Interior Improvement Center > Doors, Skylights and Windows
Reload this Page >

Need advice on installing Pella Thermastar Slider

Need advice on installing Pella Thermastar Slider


Old 11-30-14, 06:30 PM
Thread Starter
Join Date: Nov 2014
Location: USA
Posts: 312
Received 0 Votes on 0 Posts
Unhappy Need advice on installing Pella Thermastar Slider

I had a 4' x 4' and a 4' x 5' Pella Thermastar Slider to install.
It took some persuading, but I was able to install the 4' x 4' unit so that it is level and the sliding window opens and closes fairly easily.
The 4' x 6' unit, however, is giving me fits. If I level the sill, the jamb goes out of level. If I get both the sill and the jamb to be reasonably level, the reveal between the edge of the sliding window and the jamb is slanted. When I think I have reasonable level, the slider is difficult to open.
I feel like I'm trying to make Jello straight and level.

Do you have any tips on how I can tame this install?

Thanks in advance.

BTW. I hope this is an appropriate forum. I didn't find one that focuses on windows.
Sponsored Links
Old 11-30-14, 07:40 PM
Gunguy45's Avatar
Super Moderator
Join Date: Dec 2007
Location: USA
Posts: 21,119
Received 3 Votes on 3 Posts
Moved it for you. This is odd...why are doors skylights and windows in "Interior Improvements". We'll address that.......

Sorry, can't help with the question.
Old 12-03-14, 07:59 AM
Thread Starter
Join Date: Nov 2014
Location: USA
Posts: 312
Received 0 Votes on 0 Posts
I'll ask the question in a different way.
Have any of you experienced problems installing Pella Thermastar Slider windows? If so, how did you get past them?

Thank you.
Old 12-03-14, 03:33 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 25,843
Received 642 Votes on 594 Posts
Basically you need to use a long level to install a long window. Use a 6ft level to install a 6ft window. Otherwise it's more likely to get off, since the middle could bow up or down just slightly and throw everything off. If your sash is 2' x 4' for example, and one end of a sliding sash that is 2ft wide sags just 1/16", it will affect the side that's 4ft tall at least twice that... 1/8".

You didn't say if it has a nailing fin or if this is a retrofit installation. A vinyl window generally needs to have more support than just hanging from a nailing fin. So while you may "start" by leveling the sill, and putting a few temporary screws in the nail fin, you would have to add shims to the interior perimeter as needed, or else the weight of the sashes will affect the way they plumb up when they meet the jambs.

In a nutshell, the sill should be level. The entire frame should be SQUARE when measured diagonally from corner to corner. If it's 80 1/8" from corner to corner, when you check the opposite diagonal, it should be exactly the same. Keep in mind that just because the outside of the window (where the nailing fin is) is straight, that doesn't mean the inside (where the sashes slide) is straight. So check both with the longest level you have. On the interior, I would say you need to shim the bottom of the window every 16". If there is no space under the window, and it's just resting on the rough opening, then it's possible that it's conforming to the shape of the opening which might be bowed up or down.

Once you have the bottom level and straight, inside and out, forget about plumb for now... measure your diagonals and make sure it's square. If the bottom is really level and the window is really square, the sides should automatically be plumb. Slide your sashes almost closed. The gap where the sash almost meets the jamb should be straight... like a 1/8" gap all the way up. If it's tight on top and gapped on bottom, you may have shimmed the bottom of the window (interior side) too much on the lock side of that sliding sash.

You also want to measure the window across the frame, at the top, middle and bottom, and make sure the sides are parallel. Do the same thing to check the height... check the space between the top and bottom frame at each end, and make sure that measurement is the same all the way across the height of the window. If it's too tight, the windows will be hard to slide.

I suppose it's also possible that if the window is bowed in or out that might cause a problem. Longer windows usually need a couple screws to prevent the frame from bowing in or out. (especially when a retrofit window is sitting on a sloped sill, it will want to slide downhill in the middle and bow outward).

If you have some specific question, just ask. And be descriptive... we can't see what you see.
Old 12-03-14, 08:14 PM
Thread Starter
Join Date: Nov 2014
Location: USA
Posts: 312
Received 0 Votes on 0 Posts
Thanks for your ideas XSleeper. You've given me some more things to check.
It is a new construction window, i.e., it has a nail fin.
I do think there is a slight inward bow on one side jamb, so I believe the only way I can correct that is by pushing outward on the jamb when I screw the fin on that jamb's side.
The best I have is a 4' level.
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: