Advice on adding 2 rads to a Combi installation

[muffking]

Hi Guys.
I've had my CH installed for 3 years now & need another coupld of rads adding.

It's a sealed Baxi 105e running 7 rads (2 of which are very small singles), but I need to add a tall thin rad in the downstairs hallway and a larger one (around a 600x1000 double) in the upstairs hallway.

I'm happy to flush the system & have done some pipework before when one of the valves siezed, but I don't fully understand the flow circuit(s) from the boiler and need to know if I can just add them to one of the 10mm supply/returns from another rad?

 

[Bahco]

can I just add them to one of the 10mm supply/returns from another rad?

Definitely not.

You should really come off the 22 mm flow and return.

Tee off in 15 mm (from the 22 mm pipes) and split this feed to your two new rads which should heat up quickly.

Balance your system after.

 

[muffking]

Sorry, I meant to say that they are 15mm pipes, not 10mm

I have the plastic pipes running under the floor boards right past where I want to add 1 of the rads, but if I tap into the supply or return & turn the TRV off on the new rad won't that stop the flow through the other rads in the same circuit?

 

[ChrisR]

The rads should be in parallel, like bulbs on a 12V circuit, so turning one off doesn't affect the others. Much!
You can add a small rad to a 15mm circuit if it isn't being used for more than about 3 kW. For bigger rads you need to go further "back" to where the pipes are bigger.

 

[muffking]

Thanks Chris, that makes perfect sense.
One of the rads will be around a 600 x 1000 single, but I have little room on the wall for the one downstairs which is proving more difficult to find a narrow rad (around 300mm wide).