How to add another radiator to a microbore system?

[Simon Hawthorne]

Hi all

Just finished the job I started last week - fitting a TRV to one of my radiators on my microbore system. Actually removed the rad yesterday, flushed it out with a hosepipe- then cleaned the threads for the valves with a toothbrush - used '5 turns' of tape on the valve threads

- and reconnected. Dry as a bone now!

Anyway, I would like to add another rad to the downstairs circuit. As far as I can see, the circuit of fed on a 22mm pipe from the boiler to a manifold - where lots of 8mm pipe branches off the the rads. The retur pipes are the same. To add another rad, can I simply but an equal T joint into one of the micorbore feeds, and the same on the return? If I do it on the feed to the closest existing radiator, will it work?

I understand that there would be a temperature drop in the existing rad, but that is the one I have fitted a TRV to - because the room gets very warm - so shouldn't be a problem. I only want to run about

4m of pipe from it - and put on a small new rad in a corner of the kitchen that is about 18 feet from the nearest other rad - and gets quite cool...

Thanks in advance

Simon

[Set Square]

There are rules of thumb (which I'm sure others will quote) about how much heating capacity you can get from an 8mm pipe. If it's less than the combined output of your two radiators, then you shouldn't be doing it. I've never used microbore, but my understanding is that it's usual to have individual feeds for each radiator from the manifolds. Have you got any spare tappings on the manifolds? The other alternative is to tap into the

22mm flow and return pipes using 22x22x8 tees.

[Simon Hawthorne]

Hi SS

Nope - the manifold is not like the one upstairs - the end of the feed pipe from the boiler ends in what looks like a load of 'tentacles' - which just spout straight from the end of the pipe.

I like the idea of the 22mm into 8mm though - but that would be in the pipe before the manifold/tentacle split - suppose it should be OK. I think, depending on flow, 8mm pipe can supply 4kw - and this is far more than the two rads that would be on the pipe.

I can't find any 22mm/8mm tees - so might have to go 22mm to 15mm then down to 8mm....

Thanks for your help

Simon

[Cicero]

=============== What you're proposing will certainly work provided that the heat loss to the original radiator is acceptable.

Tee-ing into the two 8mm pipes (flow and return) will be much easier than trying to Tee into the 22mm pipes because you'll be able to bend the 8mm pipes to insert the 8mm Tee. The 22mm pipes will be fixed quite firmly and you may not be able to get Tees in without substantial dismantling.

Cic.

[Andy Hall]

It depends on the radiator sizings, Simon. Over a few metres, 8mm tube will support 1500W. So take a look at the sizing and calculate the rating of the existing radiator. Obviously if the room is getting very warm some under-running may be OK. There would be some interaction between the radiator behaviours if you tap off near the first radiator, less if you tap off nearer the manifold. As long as you're not trying to get more than about 2kW or so in total it should be reasonable, albeit it not ideal

It would be better to plumb back to the 22mm.

[Set Square]

BES 7231 looks like it would do the job - albeit at a silly price!

If you *do* tap into the flow and return pipes, make sure that you do it on the right site of any zone valves you might have in your system - otherwise you might have a red hot radiator in the middle of summer!

[Andy Hall]

Ah, one of those. It's still a manifold.

That would be a way.

If you think you might add more radiators later, it would be better to purchase a slightly different type of manifold which comes with blanking plugs. Attach this to the existing 22mm feed using a

22x22x22 tee.