Central heating long lengths of 15mm

Hi Everyone,

I've got the ceilings down in a house I'm renovating and looking at the central heating setup.

I have 22mm pipe coming from the boiler and running down my landing and then returning to the boiler.

There are 15mm tees off to the radiators in each room, but some of these runs are very long due to the size of the rooms, easily 10+ metres of 15mm in some of the rooms.

Would it be worth me extending the main 22mm pipes so that they run into each room then teeing off in 15mm much closer to the radiators?

 

A single radiator only needs 15mm pipe so no. I assume it all works. If it aint broke don't fix it.

 

There are limits , friction being one..

 

True, but as I said:

I assume it all works. If it aint broke don't fix it.

 

If you really thought there was any pipe sizing problem you would need to measure the flow and return temps at any suspect rad.

But as recommended above there is no point in trying to fix a problem which does not exist.

Tony

 

Well, I'm only planning on having the ceilings down once. And it's a hell of a lot easier to change pipes from below with all of the ceilings down (this is a massive period house), rather than lifting floorboards from above and tracing pipes at some point in the future.

The only "problems" I have with the current setup is the pipes have been notched into the joists and sit tightly under the floorboards. This causes clicking and leaves no room for the pipes to be insulated.

So while the ceilings are down I plan to make some improvements, but just wondered whether it would be worth extending the primary circs so there's more 22mm and less 15mm while I was doing it.

Thanks all

 

The smaller the pipe diameter, the more powerful the pump will need to be to maintain the minimum circulation required by the boiler. I had to upgrade to a semi commercial pump for precisely this reason. As said, though, if everything is working with your current setup, there's no *need* to upgrade it. However, if you are having to use a fairly large pump (and probably more expensive), or if you are experiencing excessive noise from high velocity water, there may be benefits to doing the work.

 

No.

 

Ok thanks everyone.

I have another really stupid question if that's ok.

Should the 22mm main circs create a complete circuit back to the boiler with all rads tee-d off in 15mm?

OR

Should the 22mm flow run to a radiator (with a reducer to 15mm) and then the return from this radiator goes into the 22mm return to the boiler, with all other radiators then teed off in 15mm? So essentially this 1 radiator forms part of the main circulation, with all others tee-d off the flow and return?

Does that even make sense?

My setup is pressurised with an unvented cylinder.

 

Most of the water will flow along the 22mm and by pass the radiator.

 

So should it be option 1 or option 2?

Currently my setup is option 1.

 

If you want the radiator to heat up then you need the water to flow through the radiator.
That happens best with option one.

 

option 1 is correct
option 2 is known as a one pipe system

 

But all other radiators will be teed off the main 22mm pipe so I don't understand why it would make a difference?

 

The difference is that Option 2 short circuits all of the radiators and will be the path of least resistance - meaning water will always try and flow through that path rather than where you want it to go (i.e. through the radiators).