22 mm how long to 15mm

[hamd01]

I'm just in the process of laying some 22mm flow and return piping in an extension.

Is there a standard practice in terms of the length of 15 mm pipe going to your radiators. It's going to make the job a lot easier if I run the 22 mil in a large rectangle around the room roughly one meter away from the wall... However is it acceptable to come off the 22 with one meter of 15 millimeter to the rads or is that considered too long?

 

[muggles]

Depends on the total load on the system. You might not need 22mm at all, 15mm all the way may well be enough. Proper heating system design targets a 0.9m/s velocity in the pipework. Oversized pipework leads to sludge buildup, undersized pipework leads to noise. Essentially, if you want the properly correct answer, it needs to be calculated rather than guessed

 

[Jurassicspark]

Oversized pipework leads to sludge buildup,

Could you explain the reason behind this?

Thank you.

 

[muggles]

Oversized pipework will have a lower velocity. System debris will not remain in suspension below about 0.3m/s and so will deposit in pipework

 

[hamd01]

Oversized pipework will have a lower velocity. System debris will not remain in suspension below about 0.3m/s and so will deposit in pipework

Awesome thread hijacking.

 

[muggles]

Awesome thread hijacking.

Not at all, it's very relevant to your original question

 

[Madrab]

The answer to the question is yes, there is a standard and that's not to guess and to perform specific calculations - https://myboiler.com/calculators/pipe-size-calculator/. There is no real max or min, as was explained quite specifically, it's all about the system size and requirements tied to specific standard design specs. A guessed answer or wrong information could cause the system to form deposits over time and/or not perform properly or efficiently.

As far as Hi-jacking a post is concerned, the person asking a supplementary question would be the one deemed to be hi-jacking and not the one answering and that wasn't @muggles. Asking a question that doesn't relate directly to the OP or the answer given about pipe sizing and lengths and going off topic would be hi-jacking but asking and answering a supplementary question directly related to the original question and answer isn't.

 

[hamd01]

So based on the feedback Ive decided to do some calculations. I must admit, Ive had 6 houses over the years, and had the heating system either installed from scratch or by qualified plumbers. I must have had 10+ rads added to the systems at various points too..... honestly, I dont think ive ever seen a plumber perform any kind of calculation, and when adding rads on I dont think ive seen them do anything other than feeding off the nearest 22m, down to 15mm all the way to the rad.... Ive defintly not seen a calculator out.....and ive never had any issues. However, as this is being done from scratch, and Im doing it myself (apart from the comissioning) I thought Id plan it out properly;

Its a build seperate to the main house, with its own 30kw boiler. Its 2 rooms, both on the same level.

Room1 will have two radiators, both 5849 BTU rated.
Room 2 will also have 2 radiators also rated 5849 btu.
radiator 1 in room 1 is 3m away from the boiler.
radiator 2 in room 1 is 7 meters from the boiler.
Radiator 1 in room 2 is 10m from the boiler.
radiator 2 in room 2 is 15m from the boiler.


Each radiator is rated at 5849 BTU.

Room 1 Total Heat Load:
2
×
5849
=
11698

BTU
2×5849=11698BTU
Room 2 Total Heat Load:
2
×
5849
=
11698

BTU
2×5849=11698BTU
Total heat load for the system:
11698

BTU
+
11698

BTU
=
23396

BTU
11698BTU+11698BTU=23396BTU

Boiler to Radiator 1 in Room 1 (3m):

I believe 15mm pipe is sufficient since it can handle up to 15000 BTU/h, and the load is 5849 BTU.

Boiler to Radiator 2 in Room 1 (7m):

The total load up to Radiator 2 will be 11698 BTU. So15mm pipe

Boiler to Radiator 1 in Room 2 (10m):

The total load up to Radiator 1 in Room 2 will be 17547 BTU (11698 BTU from Room 1 + 5849 BTU for Radiator 1 in Room 2). So a 22mm pipe here because a 15mm pipe would be too close to max.

Boiler to Radiator 2 in Room 2 (15m):

The total load up to Radiator 2 in Room 2 will be 23396 BTU. So A 22mm pipe.

Detailed Pipe Layout
From Boiler to Junction for Room 1 and Room 2: Use 22mm pipe.
From Junction to Radiator 1 in Room 1: Use 15mm pipe (3m).
From Junction to Radiator 2 in Room 1: Continue with 15mm pipe (total distance 7m).
From Junction to Radiator 1 in Room 2: Use 22mm pipe up to the point before Radiator 1 (10m), then reduce to 15mm pipe to the radiator.
From Radiator 1 in Room 2 to Radiator 2 in Room 2: Continue with 15mm pipe (total distance 15m).

Summary of Pipe Sizes
Boiler to Split Point: 22mm
Split Point to Radiator 1 in Room 1: 15mm (3m)
Split Point to Radiator 2 in Room 1: 15mm (7m)
Split Point to Radiator 1 in Room 2: 22mm (10m), then 15mm to the radiator
Radiator 1 in Room 2 to Radiator 2 in Room 2: 15mm (15m)

Plan
Ive done a little plan as follows

Be interested to here is you guys think this is ok.

 

[hamd01]

Well that provoked an earth shattering silence.

 

[muggles]

Yeah, your use of BTUs which haven't been the standard measurement for heating power since the 1970s was somewhat off-putting. All my charts & calculator are in watts and I couldn't quite work up the enthusiasm to convert all your measurements across when I saw your post late last night. Might get time to look at it later for you.

 

[Madrab]

Multiply all your BTU's by 0.293 and that convert over to W.