Window quotes are hard to compare because they describe different work under the same heading. Three bids on one house routinely spread forty percent, and the spread is usually real — different methods, different glass, different scope — rather than different margins.
Eight items make a quote comparable.
1. Method, per opening
Insert or full frame, stated for each window rather than for the job. Mixed jobs are normal and common, and a quote that does not distinguish them is hiding the largest single cost variable.
2. The NFRC numbers, per window type
U-factor and SHGC for each configuration on the order — the picture windows, the casements and the sliders will differ. One number for the whole house is the best number in the catalogue, not the number you are buying.
3. Operating type and net clear opening
Which windows open, how, and for bedrooms the net clear opening figure. This is the line that catches an egress problem before manufacture rather than after.
4. What happens to the trim
Interior casing and stool: reused, replaced, or replaced in a named material. Exterior: capping in aluminium coil, new trim, or existing left in place. On a full frame job the trim is a real cost and it is frequently left vague.
5. Flashing and air sealing, named
"Installed to manufacturer specification" is not a specification. What should appear: sill pan, jamb and head flashing lapped in the correct order, low-expansion foam or backer rod and sealant at the perimeter, and interior air seal.
This is the difference between a window that leaks in five years and one that does not, and it is invisible once the trim goes on.
6. Disposal, and lead
Removal and disposal of the old units. For a house built before 1978, the contractor must be EPA RRP certified for lead-safe work practices, and the containment and clean-up that requires is a genuine cost line rather than a formality.
7. Two warranties, separately
The manufacturer warranty on the units — with the glass seal term stated, since it is usually different from the frame term and is the part that actually fails. And the labour warranty from the installer, which covers leaks and is typically one to ten years.
A twenty-year glass warranty from a company with a one-year labour warranty tells you where the risk sits.
8. Payment schedule
A deposit at order and the balance on completion is normal — windows are made to size and cannot be resold. A demand for the majority up front is not.
What the price will not tell you
Brand is a weak signal. Most manufacturers sell three or four tiers under one name, and the cheap line and the good line share only the badge. Ask which line, and read the NFRC numbers rather than the brand.
Per-window pricing hides the openings. A large picture window and a small bathroom unit are not the same cost, and an average across the house makes a quote with more small windows look better than it is.
A big discount for signing today is a pricing method, not a saving. The number was set to allow it.
The comparison that works
Ask each bidder to price the same method on the same openings with glass meeting the same NFRC numbers. Where a bidder disagrees with the method — recommending full frame where another recommended inserts — ask what they saw. Sometimes the answer is rot at the sill, and that bidder is the only one who looked.