Is this odd?

I've been looking under the floor in our dining room due to insulating under the floorboards and wanting to install a couple of new rads. The one in there never worked that well, and I think I know why.

There are two 22mm pipes that seem to be coming out of the boiler, I presume send and return, they both at different places turn 90 deg and head towards the front of the house where the heating works well.

Where they feed the rad in the dining room, however, both ends of the radiator are connected to the same pipe. Am I right in thinking that this would never work that well, and that this is why the rad connected in this way has never given out much heat? I even replaced it a couple of years ago (without going underneath the floor) and just assumed that it was plumbed in correctly.

There are abandoned other "legs" of 15mm pipe that look like they were connected to old radiators, but these are also both taken from the same pipe.

At least with what is there, I can use one of the unused 15mm pipes from each of the different 22mm send and return pipes to connect the new rads to.

I was wondering if it would be possible to connect quickfit (with copper to new rads where showing) right up to where I am going to join to existing copper, then quickly join the new an existing together rather than draining the system. Is this a daft idea? I don't mind getting a bit wet if it will save a couple of hours, but this may be very bad practice....

PS it does seem to be a feed/return system rather than a single pipe loop as the water enters and leaves the rads at the bottom.

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Hi, would be grateful for any responses to this bit in particular:

Where they feed the rad in the dining room, however, both ends of the radiator are connected to the same pipe. Am I right in thinking that this would never work that well, and that this is why the rad connected in this way has never given out much heat?

Read more: https://www.diynot.com/diy/threads/is-this-odd.564364/#ixzz6mOMqKmxs

Have you acertained whether the rest of the system is also connected in single pipe mode?
You will certainly see an improvement to that poorly performing radiator if you connect it in two pipe mode.
As for getting wet, have you considered hydraulically sealing the system to restrict water flow whilst you make the new connections?
1. Get the system hot.
2. Turn off the boiler and any forms of heat.
3. Seal the cold feed and open vent holes (carrots work well if you have no rubber bung)
4. Seal all automatic air vents, and all expansion vessels if fitted.
5. Bleed existing rads, then allow to cool.
You will find very little water needs to be drained to drop system pressure to zero....and you get less wet.

Thanks for reply, I think the rest of the house is two pipe, certainly upstairs seems to be and this is how new radiators were connected.

Not sure what you mean by 3&4, we have a combi boiler if that makes a difference?