Radiator pipework sizing issue

[PaulF]

Hi,

Sorry fo the length of a first post, but here goes!

I've pulled up some floorboards to move a radiator whilst decorating an old Scottish farmhouse. This has, inevitably, led on to more work on the heating system until I've got to a reasonably deep level of work.

I'm running a Worcester 12/14 and an old 12 or 14 KW Arrow solid fuel stove via a neutraliser. The radiator circuit pipework from the neutraliser, to the pump and to a point it disappears into a concrete floor is 22mm The return is the same. I have pulled up floorboards in the next room, inline with the concrete entry point, only to find it is 15mm from there to the 3 attaching rads! There are 15mm branches off the 22mm manifold for a further 4 rads.
I am looking to shuffle radiators, and reroute some of the pipes, allowing for the fact I will be doing more work at a later date.

I would prefer the manifold flow and return to be 22mm, with each rad branch being 15mm. Can I keep the buried 15mm pipe as is, and step back up to 22mm for the 5 radiators I want on now. I will be looking to replace the buried 15mm with 22 when I renovate that room?

This will mean my circuit goes from 22mm down to 15mm, feeding rad, back up to 22mm feeding a further 5 rads

I understand it is not an ideal solution, but my choice is to step up, or run the rest of the manifold on 15mm, which will hold 5 or 6 rads eventually.

Chasing out the concrete floor and relaying in 22mm is not an option at the moment, although as mentioned above, I will be able to chase in the bigger size in a year or so.

 

[Dickie]

The Flow & Return pipe size is determined by the size of the radiators, the length of the pipes, the temperature of system & the temperature difference between the Flow & Return. All of which is no job for a layman & involves more than a little knowledge & good software.

 

[PaulF]

Dickie, stop being a tit.

I fully understand the relationships between pressure, velocity and pipe diameter and am well acquainted with thermal dynamics and converging/diverging ducts.
Most 'software' will not be applicable to a N.E.Scotland, draughty old house with solid fuel room heating and central heating as the numbers are almost impossible to define for any calculations - feeling warm is subjective and heat required for a room is dependant on many things, including wind direction.

I also know that reducing down a pipe and then bringing it back up is not a great idea, however neither is running a manifold that is too small, which is why I asked if anybody has experience of the possible effect of stepping down and then up a pipe size.

When somebody asks for help on a forum such as this, trying to be smart is not clever unless (as per the gas policy) there is actual danger involved.

 

[Howsie]

You are adding resistance to the pump/circuit but apart from that I don't see an issue as long as the water can accommodate the heat transfer you need.

But you knew that already 😉

 

[AWheating]

15mm will give a max of about 6kw (11 degree difference) as a rule, you then need to take into account the other factors. from the sounds of it your going to see the rads past the 15mm struggle at a guess. The sooner you can upgrade the system the better. Wether it will work well enough to keep the property warm and livable untill its upgraded is hard to say.

 

[PaulF]

Thanks guys,

I expected the step down to give an increase in velocity, followed by a decrease when it goes back up. I think this should help reduce the effect of the smaller diameter - at the cost of the pipe eroding.
I did wonder if there may be hammering caused by the velocity changes -although being set in concrete should prevent that.

If the later rads start to struggle, I'll just have to speed up the coal shovelling!

I suspect I will try it - and post back here with the results!

(BTW, I'll NEVER be able to get it warm, although liveable is a possibility!)

 

[Howsie]

Hammering, no. Noise, yes.

 

[lame plumber]

your main issue is copper in concrete, not a good match unless its totally protected

 

[PaulF]

your main issue is copper in concrete, not a good match unless its totally protected

Yes, you're correct.
Going by the rest of the work done, I would be surprised if the concreted pipe are protected.
However, they have lasted until now and I'm expecting to chase in new ones within the next year or so and also up the size to 22 - just not now!

On a similar vein,I have a better ph in my water now I have a ph balancer in my inlet water supply - a Scottish private water system means very acidic water without one. (of course I could heat the house from the hydrogen collected in the rads :teeth_smile: )

 

[Dickie]

You're the one that knows everything about it, but yet asking the questions about the subject? And I'm the tit??!!
I thought all you teuchters in North of Scotland kept livestock in your house & bed. Do you need heat??

 

[Ermintrude]

What are you going to loose? If you are moving rads do it in 22mm and then step down to ex 15mm. If it struggles simply dig up floor or install a temporary f&r in 22mm above floor around wall of room to be later renovated, if you are chasing pipes in walls why not use John guest barrier pipe? Resistant to acid and alkaline it's designed to go in concrete floors. Pressurise pipes before covering in concrete!