22mm -> 15mm Why?

[Klorr]

A quick question.

Why is the pipe work 22mm when it leaves he combi and then goes to 15mm when it gets near the radiators and then switches back 22mm to go back into the rad.

Why not 15mm all the way round?

 

[Last Plumber]

Because all pipe sizes carry different amounts of water/fluids and are sized in order to deliver the correct or required amount ( in your query ) to each emitter.

The pipes are downsized on the way out to rads because as they pass emitters they obviously no longer need to carry the total amount or whole system requirements. On the way back they increase as once again they are carrying the whole systems water by the time you get to the boiler.

A good example of how this is designed is your Vascular system !
The aorta is a large pipe off the top of your heart and reduces in size as it needs to carry less to say, your toes. The return does the opposite and ends up the Vena Cava which is the size of, or similar size to the Aorta.

 

[jtsplumbing]

22mm pipe needed to carry the heat away from the boiler each size pipe will only transport a certain amount of heat, use to small a pipe and your system will not get to correct temperature. that's the simple answer, others I dare say will go into a more detailed explanation

 

[Klorr]

Ah, that makes sense.

So normally would the 22mm be taken to just before the first rad, half way from the combi to the first rad, etc.
Is there recommended amount (%) or distance before it goes down to 15mm

 

[Last Plumber]

It all depends on the gallons per hour required by your system.
( litres per second in today's world).
The installer should work out the flow rate required by whichever emitters are being used and size the pipes accordingly.

There are rules of thumb with domestic. Personally I like to calculate things out so I know they are correct. In commercial work we calculate everything. Pump size, pipe sizes, boiler sizes, heat exchangers, headers, valves, strainers etc.

Are you about to install a heating system ?
If you are, it is well worth paying a good heating engineer to design it for you. Even if it's just a small system with 22 and 15 mm pipe that he or she can weigh up using experience and not to much fuss. Even if it's just to give advice on what pipe sizes they would use themselves in your situation.

Their advice can save you a lot of headache in the future if it's done wrong.

 

[Best]

Most houses just simply 22mm doing the main pipe runs of flow and return with 15mm teed off to each rad. But any of the branch offs for a couple of rads might be fine with 15mm if rads not large output. Old school thought was 20,000 btus max for 15mm and 60,000 btus max for 22mm on open vent systems, but that still is a good method. Never underestimate the demand on pipework in severe weather.
Using 22mm main runs almost to last rads will balance the main circuit well IMO as the last rads tend to be hardest to heat. You can't go wrong with "too big" and great if you needed to add an extension to your property later.

 

[joni os]

Circulation water is the means of getting heat from boiler to rads. Flow, litre/min,(Mass / time), determines rate of heat transfer. Total heat load needs to leave boiler, large flow and return pipes, high flow.
Each rad requires only fraction of total heat hence smaller pipes to distribute heat to different parts of system.
An old rule of thumb was 15mm pipe is good for 15,000 BTU,( 4.5Kw). and pipe size was determined accordingly.
While my fingers were pondering Best said it better.

 

[Klorr]

Thanks for all the feedback.
No I'm not going to put in a new heating system.
Was just looking under the floor board the other day and noticed the different pipes. I was just wondering why.

 

[Last Plumber]

Thanks for all the feedback.
No I'm not going to put in a new heating system.
Was just looking under the floor board the other day and noticed the different pipes. I was just wondering why.

Get yourself a fishing rod or some golf clubs. Archery is good ! lol

 

[Klorr]

I can't work out how to upload a picture on here so this is on my Hotmail onedrive.
https://1drv.ms/i/s!AlXOOGaTv36QgQyww22CAUIlGNq0

Should it be like the top run with 22mm all the way along
Or like the 2nd run with 15mm