Adding a radiator.

[Danny]

Another one for Lee I'm guessing...

We've got an extension built years ago, and apparently they said the boiler wasn't good enough for another rad. Since then we've had a new boiler put in and the extension is absolutely freezing.
From the loft in the extension I could drill through the wall and be under the floor upstairs right next to a towel rail, so can I drain down the system, stick a t piece on the flow and return and then run 2 poly pipes down the stud to a new rad in the extension, or is there more to it than that?

[Lee]

You'll have to work out the kW of the boiler, then the kW of all the radiators together. Whatever is left will be the Max output your new radiator can be. If you choose to use plastic pipe, make sure it's the correct 15mm barrier pipe designed for central heating. You'll also need to ensure that there aren't too many radiators already being fed off the branch of pipe that feeds the towel rail or else you'll be wasting your time. Generally speaking, there should be a branch off 22mm pipe feeding a Max of 3 radiators on 15mm pipe. The system may well then need balancing to accommodate the new rad. It sounds complicated but it isn't. Get to plumb centre and get one of their trade books, they list sizes of radiators with their output.

[Danny]

Adding a radiator.

Great, thanks. I've got a screwfix catalogue here with the kW ratings in, so I'll have a look into it tomorrow.
What do you mean by it may need balancing?

[Lee]

Water takes the easiest route, and several factors can restrict the flow of water through your radiators. This can be sludge, pipe sizing/configuration, and the actual radiator valves themselves. On a radiator you have the normal radiator valve (either a manual valve or a thermostatic valve), and a balancing valve with a blank cap. What you do when the radiator is fitted, is to get your system up and running, then see if they are all coming on equally. If not you remove the blanking cap on the radiator valves, and go around the radiators opening up the ones on the radiators which aren't warm enough, and restricting down the ones which are getting hot easy. This equals out the restrictions on the system allowing all radiators to warm equally. It's a case of making any adjustments by half a turn at a time and then allowing a few mins to see if the adjustments have made a difference.
If you ever need and help or advice with any of it just pm me.

[Danny]

Brilliant, cheers. Always wondered what the second valve was for.