Radiators in series - WTF?

[Tim Streater]

Wondering why the living room rad was not getting hot, I remembered I'd turned off the one in the conservatory - common wall. Looking at that, I discover these two rads are in series, but there is the possibility to turn a screw in a pipe a 1/4-turn, opening a valve, and thereby short circuit the hot-water *around* the conservatory rad. This rad is still off and the living room one is now nice and toasty.

The bathroom also has a rad in series with the towel rail. Is there any rational reason for these sorts of arrangement?

[Andrew Gabriel]

That's a little bit like a single pipe circuit, except you wouldn't have any means to close off the "short-circuit" as you call it. It's not a short circuit actually - the radiator presents less flow resistance than that pipe, aided even further by the convection current if the radiator is losing heat to the room. I wonder if the valve was added by someone who didn't understand a single pipe circuit?

Fewer pipe runs around the room. It's not used anymore because the heat loss calcs and radiator sizing was a more expert job than installers today would cope with.

[Tim Streater]

Even, you mean, when the pipework to/from the rad has some right-angles, whereas my "short-circuit" is a straight pipe with the isolator valve in it? Interesting. (I take the point about the convection/cooling).

Certainly whoever installed a lot of this stuff did a gash job. I've got a rad half-hanging off a wall, a towel-rail rad on another wall at an angle because the installer should have cut another 1/2" off the pipe going into the wall, 1/2" pipes going into 1.5" holes ...

I'm gonna have to get a man in - but not til the weather is warmer.