> Most likely your house has double glazed windows - I only see single-glazed windows in antique wooden windows these days (but perhaps it's different outside of New England).

Internationally speaking, the UK is very far behind when it comes to insulation. Single glazed windows are still standard in many houses. Energy prices are cheap compared to the rest of the continent and costs are still one of the highest.

Here in California, pretty much any house built before 1980 is single glazed, unless it's been retrofitted.

Double glazed are quieter than single. That's a nice benefit as well.

How can you tell if a window is single, double or triple glazed? Is there an easy way, or would I have to have a specialist look at my windows?

Generally, an easy way to figure it out is to look at where the glass intersects the frame. On a single pane window you'll see the interior frame, a gap (the glass) and the exterior frame. On a double pane you'll see a gasket between the frames that separates the two panes. On a triple pane you'll see two gaskets separating the three panes.

The gaskets maintain an airspace between the glass panes, which is responsible for most of the thermal performance. On new windows this can even be filled with a transparent gas (like argon or krypton) to increase performance.

You're counting the panes of glass. So look sideways where the glass meets the frame and count the grooves.

Turn on a light inside the room (even the flashlight of your phone will do), and look outside through the window. Count the reflections of the light that you can see.