Contractor installing multiple Marvin replacement windows
25 February 2019

Window Installation Tips from the “Minnesota MacGyver” of Replacement

At Marvin, Master Installer Eric Klein is on a mission to eliminate callbacks on replacement window installations.

As an accredited instructor, he trains up to 1,500 contractors each year in residential, light commercial and door installation. His work and his reputation in the field has earned the 34-year Marvin veteran many distinctions, including his nickname as the “Minnesota MacGyver” of window installation.

Culled from years of experience in installation, Eric shares his top tips for reducing callbacks from homeowners by installing replacement windows correctly the first time.

Walk the property. He starts his once-over on challenging projects with a walk around the property. Eric observes the home’s exterior condition, including the shingles, siding and windows. “I inspected a home recently. The homeowner had replaced asphalt shingles for clay tile. The added weight caused the window jambs to bow. To avoid window problems, we downsized the replacement windows,” he explains.

Ask questions. Does the current window have an integral flange? Or no flange at all? What is the window interfacing with? Is a retro-fit installation a possibility? Bracketing? Is it a full-frame replacement? Be a problem solver by asking questions and applying the best solution.

Read the instructions. Eric says you’d be surprised by how few installers do, even in his class. “We have walls set up for installation and I will do the first install, then pair the students up and tell them to install a window. Some do their own thing without opening the instructions. Mistakes follow,” he says.

Use real shims. According to Eric, way too many contractors take shortcuts with spray foam sealant, using it as quick-fix replacement for shims when setting windows. Follow the manufacturer’s instructions. Don’t take improper shortcuts that could lead to needless callbacks and legal liability.

Install with screws (not nails). Eric advises installers to go with screws because they’re easier to re-adjust the window if something needs changing. His pick: GRK screws of proper length and size for window and application.

Keep tolerances low. “I tell students to measure to plus or minus nothing, if possible. A unit that’s out-of-square by 1/16 of an inch is acceptable. If it’s 1/8 of an inch, you have to ask yourself what am I losing, window performance or operation? If it goes to 3/16 of an inch, you lose performance. At 1/4 of an inch, you lose both,” he says.

Shim away from corners. “I shim down the frame four to six inches, not at the corners. By doing that, I take away half of the window movement versus the wall. That’s a good thing,” he explains. Don’t shim the top of the window. If the building settles, the window compresses. That means loss of operation or even damage.

Eric reminds installation pros that “a window is only as good as the install. I would say out of every ten contractors, only two to three will follow our instructions in the field.” Give yourself a competitive edge by following best practices.

For more written, video, and live replacement window installation instruction, visit