How to Install a Sash Replacement Window

How to Install a Sash Replacement Window

Trent Johnson
Feb 9, 2010

The windows in my house are over 50 years old: single paned, leaky, and water condenses on them on cold mornings. It took some courage, but I finally started replacing them, one-by-one. Now that I've successfully replaced four, I wanted to share the steps to this seemingly tough project that is completely doable.

There are two types of window upgrades out there: full replacement windows and sash replacement kit-windows. I've now successfully installed two of each type, and I can say without hesitation that I prefer sash replacement kits. After speaking to a number of windows sales people at multiple hardware stores in my area, the consensus seemed to be the following:

Replacement Windows

Pros: Offer slightly better seal and can qualify for tax incentives if the proper models are ordered (only the most energy efficient windows qualify). There is a wider range of sizes and they can be customized to your individual situation.
Cons: You lose viewable window area from the frame, they're slightly harder to install and they cost slightly more.

Sash Replacement Kits

Pros: If installed properly, they can be almost as energy efficient as replacement windows; you get more viewable area (I ended up with even more-so than my previous single paned windows); easier to install; less expensive.
Cons: Slightly less energy efficient and less sizing options.

In my experience, sash replacement kits can be installed in about 30-45 minutes and require very little skill. They can be ordered with all the standard bells and whistles including those with low-e glazing, argon filled, tempered, tinted, obscured and even a range of grille options. A couple companies make sash replacement kits, but the one I used is from MW Windows and Doors (now Ply Gem Windows).

To order, you have to go to your local hardware store or big box retailer and they'll walk you through all the options. Custom orders are rarely returnable so be sure you get your measurements correct! There are guides online on how to measure your window needs. I'd be sure to reference one of these so you can be sure you order the right product.

What You Need

  • Carpenter Hammer
  • Light Duty Pry Bar or Putty Knife
  • Phillips Screwdriver
  • Utility Knife
  • Plastic Sheeting
  • Measuring tape or ruler
  • Spray Foam (low expanding for windows and doors)

For each window you are replacing, you should also have the following:

  • Balance kit containing two balances and installation hardware
  • Sash kit containing two sash (one top and bottom), and one vinyl parting bead


1. Preparation
Remove all window coverings and exterior screens. I also put some plastic on the ground to pick up all the dust/wood and protect the floor.

2. Score the Trim
Before removing the trim, I always score it with a utility knife to ensure the paint doesn't peel, and it comes away clean. The trim that we're removing is the head stop and side stops. They're relatively flat pieces of trim about 3/4" wide that cover the sides of the window sash's to make them look nice. It's possible to install a sash replacement kit without removing any other trim (the casing) around the window; however, I decided to replace ours while I was at it since it had 50 years worth of paint built up.

3. Remove the Trim
After scoring, use a putty knife or light duty pry bar to carefully remove the stops. Make sure not to avoid using a hollow wall to lever against. Once you get a little headway, you can often use your hands to pull it out completely. You can easily save this trim (if it's in good shape) to replace when you're all done. If your window has a parting bead (can be a metal or vinyl piece that the top sash closes against), remove this too.

4. Measure and Mark
Since it was relatively cold outside, I decided to make measurements and marks before removing the sash's. Using the manufacturer's directions, I marked the position of where I would be placing the clips that hold the balances in place (3" from the bottom and top, and then two equally spaced on the sides).

5. Placing Balance Blocks
Our kit came with rubber blocks which pad the inside of the balance. Using your manufacturer's directions, place this on the back of the balance in the indicated spots. It's a bit tricky to determine which way is up, and down. Just remember that the angled side of the balance is down.

6. Removing the Old Window
At this point, I removed all visible nails, vacuumed, and cleaned our window sill (inside and out). I have yet to find an elegant way to preform the next step with the type of windows in my home. If your sash's are in any way removable, do that at this time. Most old windows require that you remove the balance and sash together. Begin by removing as many staples, nails and screws as possible from the top of the interior balance. Then slide the window up and remove the bottom fasteners. You should then be able to pry the sash out of one side of the frame, bringing with it the balance and all. Do the same for the exterior balance and sash. Be careful as the sash's are only connected to the balances with springs (in my case). Older windows will have sash weights which should be cut, and removed. The compartment where the weights once resided should be filled with insulation.

7. Preparing the Opening
Again, clean the opening as best you can removing any staples, screws or nails. Vacuum any debris, etc.

8. Placing Clips
Using the marks we made earlier, begin to place the metal clips that will soon hold the balances in place. They each attach with two screws and should be placed 1/16" from the blind stop (this is the trim that keeps the window from falling outside). The best way I've found to do this is to screw the clip in flush with the blind stop and pull it back 1/16" just before finally tightening the screws.

9. Installing the Balance
Once all the clips are installed (4 on each side in this case), you can now install the balances. The angled side sits on the sill (longer side facing out) and the flat side on the top of the jam. Start on one side and use firm pressure to press the balance into the clips. You should hear a click as it snaps into place. Ensure you hear two snaps for each of the four clips. Repeat with the other balance.

10. Installing the Sash
This is the fun part. Begin with the top sash (the one that doesn't have the lock, but has lock receptacles). Hold the sash with the pins away from you and the exterior of the window facing up (usually with a sticker on it). There are small plastic sliders in the balance in which you'll be placing the pins. Place the first pin into the plastic slider in the exterior balance and slide down just enough to be able to tilt the window and place the second pin into the plastic slider on the opposite side. Level out the window and then lift into place. A little bit of pressure is all that's required to get the sash to squeeze in between the balances. Repeat the procedure for the bottom sash, this time keeping the lock towards you and the pins away from you (exterior facing up).

11. Adjusting and Adding the Parting Bead
The sashes can be adjusted with the adjustment screw located at the top of the plastic slider in the balance. It can be tightened or loosened to allow the sashess to slide with more or less pressure, as needed. Replace the parting bead using the included vinyl parting bead.

12. Insulate
Before adding the trim, be sure to fill in any air gaps with insulation or expanding foam (the low expanding kind for windows). I used a whole bottle around the perimeter of this window.

13. Replace Trim
Replace the old trim using finish nails or use new trim. (A guide to trimming a window can be found here at ThisOldHouse.) Recess all nail heads with a nail set and hammer, then fill the holes with wood putty. Allow the putty to dry overnight before painting.

Additional Notes:
These were the steps I followed to a successful MW window sash replacement kit in my own home. Other sash replacement kits might following different steps. Be sure to read all manufacturer directions before attempting such a project of your own and if you have any questions, consult a professional.

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(Images: Trent Johnson)

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