Replacing windows to save energy: a practical guide

When do windows really need replacing?

Age alone is not the test. Look for the signs that a window has failed: rotten or warped frames, sashes that stick or will not lock, fogging between the panes of a sealed unit, and ice on the inside of the glass on cold mornings. A draught you can feel with the back of your hand on a windy day points to a poor seal. If the windows still open, close and seal, repair can be much cheaper, and new weatherstripping or caulking is a small job.

Single-pane windows and old aluminum frames without a thermal break are the clearest cases for replacement. The reasoning is the same as in our guide to heating system lifespans: decide on condition and repair history, not on a birthday.

Should windows come before insulation?

Usually not. Heat escapes through the roof, the walls, the basement and the air leaks as well as the glass, and attics and air sealing normally return more for each dollar. The upgrade priorities guide sets out that order. A home energy audit will show where your house loses heat and whether windows rank high enough to go first. Comfort and noise can justify an earlier swap, even if the energy saving is modest.

What should an efficient replacement window include?

Start with the performance numbers on the label: a low U-factor for heat loss, a solar heat gain value that suits each orientation, and a good energy rating. Then look at the pieces.

• Glazing. Double or triple panes with low-e coatings and gas fill, described in high performance glazing.
• Frame. Vinyl, fibreglass, wood and aluminum with a thermal break all work, with different maintenance, cost and look. Check the frame has insulating chambers or a break.
• Air leakage rating. A tight window matters as much as clear glass.
• Certification. Models on the official list, see ENERGY STAR certified windows.

Which installation method fits your house?

There are two broad approaches. An insert, or pocket, replacement fits a new unit inside the existing frame. It is quicker and keeps the interior trim, but the glass area shrinks slightly and any rot in the old frame stays hidden. A full-frame replacement removes the old window down to the rough opening, which allows proper flashing, insulation around the frame and repair of any damage. It costs more and disturbs the finishes.

Installation quality decides whether the numbers on the label show up in your house. Ask how the gap around the frame will be insulated and air-sealed, how the sill and flashing will shed water, and whether the work needs a permit in your municipality. Many do not, some do, so ask the contractor and the building department.

How do you compare quotes and funding?

Ask each contractor to price the same package: frame type, glass specification, insert or full-frame, trim, disposal and warranty on both product and labour. Write down the model name so that certification can be checked. Prices vary with region, size, material and year, and only written quotes give a true figure, so we do not quote a number here. The habits in how to compare a solar quote carry over well: same scope, line by line, with the warranty in writing.

Incentives for windows change over time and depend on your province and utility. Check the Government of Canada energy-efficiency pages, the provincial energy ministry and your local utility, and read the product rules before you sign. Keep the invoice and the labels either way.

Quick answers