The window replacement pitch is always the same. Your heating bill is high, your windows are old, therefore new windows will fix the bill. Every step of that is plausible and the conclusion still does not follow, because windows are a smaller share of the problem than almost anyone assumes.
What windows actually cost you
About a tenth of the air leakage. In a typical older house, gaps around floors, walls and ceilings leak roughly three times as much as the windows do. Ducts, an open fireplace and plumbing penetrations each leak more than windows too.
Some conducted heat. Single glazing does lose real heat through the glass, and upgrading it is a genuine improvement. That is the part of the sales pitch that is true.
A lot of perceived cold. A cold pane radiates away your body heat and creates a draught of falling cold air. That feels dramatic and it is why people blame windows. Feeling cold near a window is real. It is not the same as that window being the main hole in your house.
The arithmetic that gets skipped
A whole-house window replacement is one of the most expensive things a homeowner buys, because it is dozens of custom units plus the labour to remove and refit each one, plus making good the wall around them.
Set that against a share of a heating bill that was never the majority of the problem, and the payback lands in decades rather than years. Long enough that most owners sell the house first.
Ask the salesperson which share of your heat loss goes through the windows, and how they know. An honest answer is a range with a reason. A confident single figure produced without inspecting your house is a sales number.
What to do instead, in order of cost
| Fix | Rough cost | What it addresses |
|---|---|---|
| Draught-proof the frames | Very low | The gap around the window, which is the leak |
| Heavy or lined curtains | Low | Radiant loss and falling cold air at night |
| Insulating window film | Low | Adds a still air layer to single glazing |
| Secondary glazing | Medium | Most of the glazing benefit, keeps the frames |
| Full replacement | High | Everything, plus the frames and the look |
The pattern is that the cheap options address the actual leak, and the expensive option addresses the leak plus a lot of other things you may or may not want.
Secondary glazing is the option nobody mentions
A second pane fitted inside the existing window, in its own frame. It captures a large share of the thermal benefit of double glazing, keeps the original windows, and costs far less than replacement.
It is the standard answer in period properties where the original windows cannot legally be changed, and it works just as well in houses where they simply do not need to be.
When replacement is genuinely right
- The frames are rotten, or the units have failed and are misting inside.
- The windows do not open, or do not close, or are not safe to use.
- Single glazing is making a room unusable in winter and secondary glazing does not suit the opening.
- You are already renovating the wall around them.
- You want the house to look different, which is a completely legitimate reason to spend money.
All of those are good reasons. Notice that none of them is the heating bill.
Questions people ask
Is triple glazing worth the extra over double?
In a very cold climate, or in a house that is already well sealed and insulated, it can be. In a leaky house it is a refinement on top of an unsolved problem.
What is the misting between the panes?
The seal on the sealed unit has failed and moisture is inside the glazing. Often the glazed unit can be replaced without changing the whole window, which is far cheaper.
Do new windows add value to the house?
They can help a sale, particularly if the old ones look bad. Treat that as a presentation benefit rather than an energy return.
Does window film actually work?
Insulating film adds a trapped air layer and does reduce loss through single glazing. It is not invisible and it is not permanent, and for the price it does more than its reputation suggests.
Where these figures come from
- Energy Saver, the Department of Energy home efficiency guide US Department of Energy
- Use of energy in homes US Energy Information Administration
Figures last checked September 2026.
