I love how with Google you can type in half a question, and see what via the “suggestions” what the most common related questions are. For example, if you type in “Why are radiators”, you will see that although many people want to know why radiators are black (or white), and many want to know why radiators make noise, the #1 thing that puzzles people about radiators is: Why are they under windows?
It is indeed a good question. Maybe your radiators aren’t under your windows. But if you live in an older house, there’s a good chance they are. As a dramatic example, is the living room of my friends’ S. & J.’s previous home in Portland (used without permission, because it’s past their bedtime):If you said, “But those radiators are just pouring heat out the windows!”, you’d probably be right. So why put them there? This is my hypothesis: central heating was new and exciting, and for the first time it was possible to design a house so that every room, and indeed every part of every room, was virtually the same temperature. I suspect people idealized a home where you could drift from cupboard to dining table to sofa to window-seat and not feel a “chill”. To achieve that, to really even out the heat, the best place to put the heat source was right in coldest place– which, before the days of weatherstripping and triple-glazing, was bound to be close to the windows.
This worked out well with the advent of coal and oil heat. Until the 1970’s or so, fuel was relatively cheap and plentiful, and burning it was relatively easy. Efficiency and conservation do not seem to have been the watchwords of the day. But times have changed, and now people seem to be mystified by why their radiators are placed where they are. Some people want to fix the “mistake” of the original installer. Here’s a project someone posted for making these diverters to channel hot air away from a cold window:You might ask, then– why not relocate the radiators away from the exterior walls altogether? Why not move them to the walls closer to the center of the house? You’d sacrifice something in evenness of heat, but gain quite a bit of efficiency. Has anyone ever thought of this?
Well, of course they have. If you’ve travelled in New England, you’ve probably seen 18th century houses in the “center chimney” style. This design was the exact opposite of the radiators-under-windows scheme. All the heat was produced in fireplaces clustered around the center of the house, which was the “warm zone”. The areas close to the windows and exterior walls were probably frigid. This is a schematic I drew to illustrate the difference in heating philosophy:And, here are some photos of an actual 1783 New Hampshire specimen in a real estate listing (to better appreciate the layout, or to buy the house, check out the “360° Tour” on the listing page)
In order to service fireplaces on several (possibly as many as four) sides, and on multiple floors, the central chimney might be truly massive. Here’s a photo showing the enormous size of the chimney foundation in the cellar of such a house in Connecticut (from the website of an appreciative broker):Bruce Irving, in his recent book New England Icons, provides a short chapter all about the center-chimney design . He writes, “As a heating plant, it was a terrific check to the long, severe New England winters. A huge mass of bricks hosting multiple fireplaces and run through with flues carrying hot gases, it acted as a giant thermal mass, holding heat and radiating it outward from the core of the house.” The main drawback, apparently, was not so much the cold at the periphery of the rooms, as the awkward floor plan and obstructed “flow” dictated by having a huge monolith in the center of your home. According to Irving, improvements in fireplace performance eventually allowed the fireplaces to migrate to the ends of the house, freeing up the middle. (Irving references Melville’s essay “I And My Chimney“, in which the writer wryly documents a war of attrition with his wife over the question of whether their house should be modernized by the removal of the center chimney. I commend it to you for historical, if not literary, merit.)
So it seems that the move away from truly central central heating (to what I would call peripheral central heating) began as improved technology allowed for increased concessions to fashion and comfort. It is easy to see how house-end fireplaces could transition into under-window radiators. But now, as efficiency again becomes of interest, things might edge backwards.