I'm adding another radiator to a room; it'll be on the outside wall the same as the present one. The gap will be only about 10cm or so, room to get valves in. Instead of fitting valves to both rads., I was wondering about just connecting them in series with a bit of pipe. Is there any major drawback to this method?
No bigee, just treat them as one when balancing ie maintain the drop across the pair rather than each in turn. Technically you will get a better result if you join both top and bottom with pipes but I don't have figures on the difference (I'd expect it to be small).
One drawback is that if one rad develops a fault you will not be able to isolate it, and moving the rads as a pair might be fiddly and require care not to get black goo everywhere if you have to loosen the joiner pipe. Minor details but worth thinking about if you have nice carpets. [ Yes folks, I'm stingy, and prefer to empty one rad at a time if I can, rather than keep forking out for expensive inhibitors etc after draining the whole system.]
If the radiators are largish, I would avoid putting 2 in series. The second one would be cooler and less efficient. I also can't see how you could fit thermastic valves which would work for both rooms.
If you were hell beint on fitting them both in series I would consider fitting a top pipe as well. Then both rads would have similar top to bottom temperature gradients.
You ought be able to get right angle lockshield valves within 10cm.
Two 2m radiators in series with pipes joined top and bottom are no less efficient than a single 4m radiator when the temperature drop across the pair is the same as the drop across the single long one.
Done it: increased the distance to ~12cm, 2 angle valves and a 'U' of copper at the bottom. Couldn't join the tops as the rads. have no top unions, only bleed.
That's what I've found, Fred: fully open vlves (well, half a turn in) between the rads and the other 2 open the right amount and lots of heat! - but why was I doing this when the temperature in the house was 22C?!!
Added some gunk and filled the system, heated it up a couple of times to get it all mixed in, now leave it for a week, drain down, wash through and refill with a drop more gunk in it - that, I hope, will do it for a few years.
Awkward job getting the additive in as only 1 rad. with top unions. Used a right-angle of pipe on a service valve and a 60ml syringe. Made the mistake of filling the system intending to drain down a bit and add upstairs, then found that I couldn't seal into a bleed hole. Had to turn off all valves except the new one and bow some water out of that to get access.
By the time it needs doing again I'll have forgotten how I did it.
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