15mm or 22mm to add more rads?

[pohnjiper]

Hi,

I have a combi boiler which is in the garage & 22mm pipes leave the boiler & rise upwards through the garage ceiling. At some point I'm guessing the 22mm pipes drop down to the ground floor. I have found the 15mm pipework that feeds 5 rads on the ground floor.
I am having some internal walls taken down & a conservatory built & want to add 3 more rads to the ground floor.
Will it be ok to T-Off from the existing 15mm pipework for the 3 new rads or should I run 22mm through the centre of the groundfloor & T-Off in 15mm to all the rads?
If I do T-Off from the existing 15mm will there be any adverse affects to the system?

 

[cr0ft]

I wouldn't recommend ever running more than 3 radiators on one 15mm branch. It's far better practise to tee off the main flow/return pipes for each radiator if possible.

You might get away with more radiators but I wouldn't hook up more than 13.5K btus worth of radiators to one 15mm pipe run.

Adverse effects are likely to be limited to you not being able to run all the radiators on the branch at once, i.e. some will not heat up sufficiently if at all. You will most likely find it impossible to balance these radiators.

 

[pohnjiper]

Thanks Keiran,

finding the main 22mm is proving more difficult than I thought it would!!

I've had various boards up, not an easy job as they are tongue/groove chip boards. All I can find at present is 15mm. I have found 2 x 15mm pipes that run down the centre of the house. Could these be the main flow/return or is this unlikely?

 

[shaunhighcock]

have a look at where your boiler is situated and then try to imagine the easiest route through the middle of your house... the flow and return will usually be located there with your 15mm flow and returns to rads branching off them. spending sometime and effort locating them will save you lots of probs balancing if you can balance at all. shaun

 

[doitmyself]

I wouldn't recommend ever running more than 3 radiators on one 15mm branch. It's far better practise to tee off the main flow/return pipes for each radiator if possible.

Making a general rule like that is meaningless as it all depends on the size of radiators and the design temperature differential across the radiators, which could be anything between 10 and 20C. The deciding factor is the water velocity through the pipe. If it too slow (below 0.3 metres/sec) there is a high probability of sludge collecting in horizontal pipes; if above 1.5 m/s the noise of the water flowing through pipes will probably be heard. Safer limits are 0.5 to 1.2m/sec.

You might get away with more radiators but I wouldn't hook up more than 13.5K btus worth of radiators to one 15mm pipe run.

Using the above criteria, a 15mm pipe can carry 3 to 8kW (10,200-27,300, BTU) with a 11C differential. If the differential is 20C the capacity is almost doubled.

Adverse effects are likely to be limited to you not being able to run all the radiators on the branch at once, i.e. some will not heat up sufficiently if at all. You will most likely find it impossible to balance these radiators.

Most balancing problems are caused by the person not knowing how to balance a system.

 

[Mbear]

Don't see a problem myself, I would run the pipe in 15mm if that's what's reqd space&access wise, it may take a little longer to heat certain rads but they will heat, no doubt about that aslong as the pump is big enough to cope with the extra strain.

As said above it's important the new setup is balanced properly to suit.

Long story short, it'll work mate

 

[cr0ft]

From experience I would say a flow rate of 0.9m/sec through any pipe is optimum for efficient operation of the system. This equates to 13,620BTUs through a 15mm pipe on a system operating with a temperature differential of 12 degrees C. If he is installing more radiators than this on a 15mm pipe run (highly likely with 8 radiators) they won't give out as much heat as they should be unless: -

1.) Temperature differential is increased to allow the pipe to carry more heat energy. This means the boiler has to work harder, not a good idea.
2.) Flow velocity is increased in the pipe. This will undoubtedly cause problems with noise while the system is running.

It can be done but I would strongly suggest that it's not good practise. Lets put it this way, I wouldn't install a system like this for any of my customers!

Far better to tee the extra radiators into the 22mm flow and return pipes...

 

[pipe puller]

15mm at 20 degree diff will carry 42000 btu/12.3 kw

 

[Mbear]

From experience I would say a flow rate of 0.9m/sec through any pipe is optimum for efficient operation of the system. This equates to 13,620BTUs through a 15mm pipe on a system operating with a temperature differential of 12 degrees C. If he is installing more radiators than this on a 15mm pipe run (highly likely with 8 radiators) they won't give out as much heat as they should be unless: -

1.) Temperature differential is increased to allow the pipe to carry more heat energy. This means the boiler has to work harder, not a good idea.
2.) Flow velocity is increased in the pipe. This will undoubtedly cause problems with noise while the system is running.

It can be done but I would strongly suggest that it's not good practise. Lets put it this way, I wouldn't install a system like this for any of my customers!

Far better to tee the extra radiators into the 22mm flow and return pipes...[/QUOTE]

in an ideal world yes

i think ur overthinking this mate, he could run the new rads in 8 or 10mm and it would still work.

do u seriously do all they calculations before u fit a system or rads?

this is what i do....

have a look at how big the system is,how many rads, how big is the boiler (kw) or how big does it need to be. make sure it can cope.

run 22mm from flow/return as far as they can go space&access wise(28mm if the system is massive obviously), 22mm to 10mm manifolds if small combi system, 22mm with 15mm 'T's for a slightly larger system etc.

i just go by experience and savvy myself and its never let me down if im honest

put the calculator away imho


ps croft, i only do domestic heating myself, i do concede the calculator is reqd for commercial properties.

 

[doitmyself]

From experience I would say a flow rate of 0.9m/sec through any pipe is optimum for efficient operation of the system.

How do you define optimum?

This equates to 13,620BTUs through a 15mm pipe on a system operating with a temperature differential of 12 degrees C.

Are you sure? I make it 22,346BTU (6.545kW).

In any case if you have a 1kW rad fed by 15mm pipes, the flow rate will be approx 0.15m/s, which is well below the recommended minimum. An 8 or 10mm feed would be better.

1.) Temperature differential is increased to allow the pipe to carry more heat energy. This means the boiler has to work harder, not a good idea.

But nobody has bothered to ask the OP which boiler he has, so we don't know if it designed to work with an 11C or 20C differential.

2.) Flow velocity is increased in the pipe. This will undoubtedly cause problems with noise while the system is running.

I agree about the noise. Fixed speed pumps can be a problem here, they are usually either too fast or too slow.

 

[stevetheplumber]

as a rule of thumb i dont put more than 3 medium sized rads on to a 15mm branchhow ever ive seen eightrads whole house systems running fine on 15 as said might take longer to warm but they will