15mm heating circuit

[DanDare]

Can 15mm pipes serve the heating for a whole 4 bedroom house with 2 bathrooms?

We recently had a new boiler put in the attic and the installer simply joined onto the 15mm rad circuit there. That's left us with a 15mm circuit wandering round the house, visiting the old boiler site, old tank site, and several removed rad sites... There used to be 22mm pipes running from ground to first floor, but they've been disconnected, and the water re-routed via 15mm.

The kitchen rad is furthest from the boiler and is therefore slow to heat up.
It's also underpowered. (1400 by 600 single convector serving 23m2 area about 9' ceiling height, wooden window and 8' square french doors 4-6-4 double glazed).

Can I improve the heating in the kitchen by swapping it for a double convector, or will the pipework become a limiting factor?

Should I run new 22mm flow and returns, at least down to the point where the ground floor circuit tee-s off the first floor?

Wouldn't be too difficult!

Thanks!

 

[DanDare]

...the boiler used to be in the kitchen.

The lockshield valves on the ground floor are fully open, about 1/3 turn open in the attic and somewhere in between on the first floor

 

[D_Hailsham]

Can 15mm pipes serve the heating for a whole 4 bedroom house with 2 bathrooms?

Doubt it, though it all depends on the amount of heat the pipe has to carry.
The more heat a pipe has to carry, the greater the flow rate (litres/sec); The smaller the bore of pipe, the higher the speed (metres/sec); the higher the speed, the greater the friction and noise; the greater the friction, the bigger the pump. If the bore is too great, the speed will be too slow and sludge can collect.

Which boiler do you have - make and model?

That's left us with a 15mm circuit wandering round the house, visiting the old boiler site,

Are you saying that the old boiler had 15mm connections for the central heating?

Have you had the house insulated recently, which means that you now need a smaller boiler?

 

[DanDare]

The Boiler is an Vailant ecotec plus 624

The old boiler was an ancient ideal mexico, situated in the kitchen. It had 22mm pipes serving the ground floor (splitting immediately into 15mm) and 22mm flow and returns heading upstairs to serve the 1st floor and attic conversion. (The connections from 1st floor to attic conversion were and still are 15mm)

We had the boiler moved up to the attic to save space in the kitchen.

The installer connected the boiler to the existing 15mm circuit in the attic.

We also rerouted the 22mm pipes connecting ground to first floor, but the installer ran 15mm pipes.

 

[D_Hailsham]

The Boiler is an Vailant ecotec plus 624

That boiler has 22mm conections, so why the installer used 15mm pipe is a mystery.

The old boiler ... had 22mm pipes serving the ground floor (splitting immediately into 15mm) and 22mm flow and returns heading upstairs to serve the 1st floor and attic conversion. (The connections from 1st floor to attic conversion were and still are 15mm)

That what I would expect.

The installer connected the boiler to the existing 15mm circuit in the attic.

He was being lazy.

I would re-plumb the boiler using 22 mm, connecting it to the existing 22mm pipework. You don't want 22mm connecting to 15mm and then back to 22mm on either flow or return sides.

The system will then need balancing. Read Balancing Procedure

 

[DanDare]

Thanks for your replies!

Sadly, there's no 22mm left in the heating circuit now. Only the flow and return to the hot water tank is 22mm. The 15mm heating circuit starts just past the motorised valve.

However, I could run 22mm from the motorised valve down to the first floor without too much trouble. I could tee off 15mm flow and returns to serve the attic floor, and then run the pipework down to the first floor and join the 15mm flow and returns for the 1st and ground floor onto it. Would that be enough? It would eliminate about two widths of the house from the heating loop too.

I could take the 22mm all the way to the ground floor if I had to... but it would be more messy...

Let me know if taking it to 1st floor might be sufficient!

Also, is it worth replacing the underpowered kitchen rad before doing this, or do you think it is the pipework that's making the kitchen cold? The rad does get hot - but being at the far end of the long 15mm circuit,, takes a while...

Thanks again!

 

[Agile]

That was a totally cowboy job.

Would you like to explain how you came by him and why you paid him?

Presumably he was not CORGI registered so you have no paperwork for the boiler and will have problems if there are any warramty issues?

Tony

 

[DanDare]

Hi Agile

He was recommended to us - and yes, was corgi registered. Have a pile of paperwork.

No warranty probs either, as Vaillant have already been to fix a problem with the expansion vessel in the boiler.

Sorry you think it's a cowboy job though.

What concerns you, apart from the 15mm rad circuit issue?

The heating works, but I do get the impression that it could be better - although I'm probably not the only person to be disappointed with their heating this week...

 

[Agile]

You can only run about 3-4 kW of heating through 15 mm! Even the hot water cylinder should be supplied with 22mm.

Its such a basic example of a cowboy job!

He presumably looked at you and decided he could save about £30 on smaller copper pipe.

Of course as he will not be member of any professional organisation you cannot complain to anyone ( apart from trading standards as that work does not meet the normal test of "good workmanship". )

Tony

 

[DanDare]

Thanks again for your reply Agile

He didn't do it to save copper, he did it because the existing heating circuit went past were the new boiler is and he simply joined into it - resulting in a 15mm circuit.

Am I right in thinking that if I ran 22mm pipes down to the 1st floor, tee-ing 15mm off for the attic en route, and then teeing 15mm to serve the 1st floor and 15mm to serve the ground floor, I'd be in better shape? If 15mm can carry 3-4kW, then that should be fine for each floor.

How many kW can 22mm run?

At present, the system does work, but am I right in thinking that the system will respond quicker with 22mm pipework? What other benefits... (...can I tell my wife about so she doesn't get cross with me for tinkering under the floor again...)

Thanks again

 

[D_Hailsham]

However, I could run 22mm from the motorised valve down to the first floor without too much trouble. I could tee off 15mm flow and returns to serve the attic floor, and then run the pipework down to the first floor and join the 15mm flow and returns for the 1st and ground floor onto it.

Something like this?

Untitled

• D_Hailsham
• 6 Jan 2009
• 1

Let me know if taking it to 1st floor might be sufficient!

Depends on the heating load on the ground floor. If you use the info in Stelrad Elite Catalogue, you can work out the heating load on the ground floor. Post the info and I'll tell you

is it worth replacing the underpowered kitchen rad before doing this, or do you think it is the pipework that's making the kitchen cold?

Have you always had problems with the kitchen rad, or has in only arisen since you installed the new boiler?

 

[Agile]

Thanks again for your reply Agile

He didn't do it to save copper, he did it because the existing heating circuit went past were the new boiler is and he simply joined into it - resulting in a 15mm circuit.

Thanks again

I am sorry to have to disagree with you, but of course he did it to save copper and the work involved in connecting to the right place.

It should have been in 22 mm to connect on to the 22 mm existing at the inlet to the motorised valve.

This is a complete lazy cowboy! he deserves to be taken to Court for doinf such a bad job. It really is disgusting!

If the 22 mm distribution pipework is downstairs then I would have been adding about £140 to the installation price for that segment of the work!

Tony

 

[D_Hailsham]

You can only run about 3-4 kW of heating through 15 mm!

Depends on temperature drop and max acceptable velocity (i.e noise)!

May I refer you to Small Bore heating Systems?

If the new boiler is working with a 20°C differential, a 15mm pipe can carry about 12kW. Maybe the installer was thinking of this when he put in 15mm pipe? However a 20°C drop will deduce radiator output by about 15%.

 

[Agile]

If the new boiler is working with a 20°C differential, a 15mm pipe can carry about 12kW. Maybe the installer was thinking of this when he put in 15mm pipe? However a 20°C drop will deduce radiator output by about 15%.

This is a 24 kW boiler supplying a heating load of perhaps up to 12 kW and a hot water load of also perhaps about 12 kW.

At the very least the boiler should be connected in 22 mm to the motor valve with the associated returns also in 22 mm.

Any normal installer would pipe the heating in 22 mm and then split that to 15 mm for each floor. That would be the minimum standard that most installers would work to. Many would do more!

Tony

 

[D_Hailsham]

This is a 24 kW boiler supplying a heating load of perhaps up to 12 kW and a hot water load of also perhaps about 12 kW.

The usual allowance for hot water is to add another 2-3kW to the heating load, not 12kW. The water will heat up very quickly.

At the very least the boiler should be connected in 22 mm to the motor valve with the associated returns also in 22 mm.

Any normal installer would pipe the heating in 22 mm and then split that to 15 mm for each floor.

Agreed in principle, but the OP may be able to get away with 15mm down to the ground floor, if the load is not more than about 6kW.

Using too large a pipe can lead to sludge build up as the velocity is too low.