Windows in North Dakota announce themselves in the heating season. Ice on the inside glass, a sash you cannot touch, and a room that will not warm are the report. The glass is not just old. It is the place the heat is leaving while the burner runs. Wind on the valley and on the open west makes the windward rooms worse, because infiltration and cold glass stack. Count those rooms before you talk about a whole-house package.
Fog between panes, rotten sills under years of condensation, and a meeting rail that misses are the mechanical facts. Insert replacement leaves the frame. Full-frame work opens the wall, which you can do in winter if the opening is managed, and which you should do if the wood is soft. Leaving a punky sill under new glass is how the ice returns. Storm panels and weatherstrip are fair repairs when the unit is square and the sill is dry.
Ask for the U-factor of the whole unit, not a slogan about the glass alone. That figure is a lab comparison. It is not a promise that the house will use less of anything. What you should feel is less ice and fewer rooms you have abandoned. Ask how the gap is filled and how the sill sheds the condensation that will still happen in a tight house with a steamy kitchen. A pretty unit set in a cold, uninsulated opening will still drip.
Rental houses and older main streets often carry the worst sashes, and the heating system gets blamed. Campus-style turnover and long vacant stretches make it worse, because nobody owns the draft. Say if the window is in a room over a garage or on the north wall. Those openings decide whether the furnace can ever catch up. Photograph the ice and the stained stool before they are wiped up and painted.
Say how many windows, which rooms you cannot heat, and whether the sills are soft. Name the town. If the policy is part of a larger freeze claim, have the deductible ready and keep the glass facts separate. The ice will be back on the next hard night. Call the number on this page.