radiator query

[dexion]

hi guys,

in the middle of a big renovation of my house and fitting new trendy rads but have a strange issue.

i've seen this when replacing radiators downstairs and wondered about it then but now its got me confused. there are two pipes going to the rad as usual; supply and return but across these pipes right in front of the rad is a pipe conecting them. this seems to short circuit the pressure difference across the rad and i cant see how any water would be inclined to flow through the rad. it did previously get hot when the old rad was fitted and i'd not been aware of the issue so what does this this pipe do? i always assumed that the heating system was similar to to an electrical circuit and you simply paralelled the rads?

 

[Rob]

Its a by-pass. Allows circulation even if rads shut off

 

[dexion]

Its a by-pass. Allows circulation even if rads shut off

ah i see - but why would water want to flow through the rad under normal circumstances? would it not be sensible to have one global pipe perhaps with a pressure relief valve? to provide this service why lots of them?

 

[seco services]

single pipe system.

 

[dexion]

single pipe system.

what does that mean?

 

[dextrous]

single pipe system.

what does that mean?

It means that the central heating has one loop of pipework, instead of the preferential 2 pipes (one for flow and one for return). Bit like having an electrical ring circuit with all sockets being taken off this as spurs.

 

[seco services]

its a single pipe loop and the rad tees off that.
the pipe across is for the flow to continue if the rad is shut off.

 

[dexion]

so the rads are essentially in series rather than parallel? if this is so why would anyone do this - just to save copper pipe? would this also expalin why its difficult to balance the system?

 

[dextrous]

so the rads are essentially in series rather than parallel? if this is so why would anyone do this - just to save copper pipe? would this also expalin why its difficult to balance the system?

Quicker and cheaper to install, not done anymore really. And yes, it makes it essential to balance the system as the rads at the end of the loop will naturally be cooler than those at the start for obvious reasons. You can get TRVs for one-pipe systems, but they tend to be more expensive.

 

[dexion]

im tempted to squash the pipe which is in parallel with tha rads is this bad idea?

 

[dexion]

looked again and there are 2 pipes going to each rad which i assumed to be supply and return. every rad however seems to have a 'sorting' pipe directly across it! if they were in series why are there 2 pipes to each rad?

 

[Nige F]

Water goes IN one and OUT the other one

 

[dexion]

Water goes IN one and OUT the other one

obviously! what i mean is there are two copper pipes under the floor heading towards each rad from the central heating system. each of these pipes goes to one end of each rad but the pair of pipes are 'shorted out' under the floor before they reach each rad so if the shorting pipe was not there it would like there was a supply pipe and a return pipe from the boiler.

 

[bengasman]

Whilst it could be a "proper" one pipe system, I have seen diy jobs on more than one occasion that were partially 2-pipe, and partially 1-pipe, with these "balance pipes" or "by-passes" added. Usually impossible to get it working properly.

 

[D_Hailsham]

A pic of the rad and piping would help.

A two pipe system is like a ladder. One side is the flow, the other the return. The rungs are the radiators.

A single pipe system is a chain of radiators, the water goes through each one in sequence. To enable one radiator to be shut off without affecting the others, you insert a bypass between the input and output of each rad. This then has to be adjusted, otherwise the water would not flow through the rad.

Also, because the rads are in series, the flow and return temperatures decrease over the length of the chain. This means the rads get progressively larger than would be necessary if they were parallel.