Is this pipework to small for flow and return.

[stanna58]

Hi All

Just moved into a detached 1900's house that is fitted with a Baxi 105E combi. I have noticed that all pipework on flow and return including to/from the boiler is 15mm only.

I have 9 rads 5 of which are doubles and large.
They all get hot really well so no flow problems. Should i re-pipe in 22 while im doing up the house or is this ok?

Cheers for looking.

Stan

 

[PrenticeBoyofDerry]

If they are all getting hot, then it can be assumed the pipework is adequate for the current heating demand. Many systems use 8mm pipe on long runs and that does the job.

 

[gasbusters]

15mm is more than big enough. As mentioned above, many systems are still on 8mm or 10mm pipes and they run perfectly fine.

The only time you will get a problem is if theres debris/sludge in the system that builds up and causes a blockage. That risk can be greatly reduced by fitting a central heating filter on the return pipe close to the boiler. If you dont have one id recommend you get one fitted. Wont cost much but they are very good at keeping the system clean.

I do quite a few boiler services and cleaning the filter is something I always do, its surprising how much debris they collect. Without the filter that muck would be getting into the boiler components and eventually cause the pump and other mechanical components to fail.

 

[stanna58]

Thanks Fellas.
Ive always thought it was 22mm to and from boiler and branch off in 15 or 10mm. I got hold of installation manual and it states 22 but if its ok it saves me a big job.
Cheers

 

[Gasguru]

Sorry to p1ss on your parade but 15mm from the boiler is unlikely to be sufficient unless you're heating a small flat and with 9 rads it appears you live in a 3 bed house or more and probably poorly insulated too.

Under the old design guides the recommended maximum heat load a 15mm pipe would carry was around 21,000 Btus (around 6Kw) to avoid excessive pipe velocity (risking noise and erosion) and excessive friction (head loss).

Although the radiators appear to heat up now you should not assume they will do so when it's snowing outside and you need the full output from the radiators.

Take the opportunity to upgrade the 15mm pipework where necessary. When you come to replace the boiler the headloss through the boiler will be significantly more with the new heat exchanger designs and by retaining the 15mm you are likely to have problems despite the fact that current design guides have in effect doubled the heat capacity of the pipework (ie. running with slower water velocities).

Pipework sizing is based on design principles...not guessed at. Large domestic houses often have 35mm pipework, it's done for a reason.