Pipework sizing.

[kenco]

Are there any good web sites that can help me check the size that my boiler primary main should be, as I am unsure that the plumber has installed a large enough bore pipe.

System:-

Sealed Unvented system
Baxi 100HE condensing boiler (gas)
Santon premier plus 210L tank
Polypipe underfloor heating downstairs
Rads upstairs and loft (all on TRV's + 1 not (bypass))

 

[sterose]

Are there any good web sites that can help me check the size that my boiler primary main should be, as I am unsure that the plumber has installed a large enough bore pipe.

System:-

Sealed Unvented system
Baxi 100HE condensing boiler (gas)
Santon premier plus 210L tank
Polypipe underfloor heating downstairs
Rads upstairs and loft (all on TRV's + 1 not (bypass))

If you had included more information on your actual problem, ie. current pipe size, we could have answered your question.

 

[CH4]

There's a pdf document HERE that explains how to calculate pipe sizes for domestic gas pipework, but posting more details, as sterose suggested, might be a quicker solution.

 

[AlanE]

Is Kenco refering to size of gas pipe or water pipe sizing??

Alan

 

[CH4]

Good point Alan. The same website also provides pdf documents about water pipe sizing: PART 1 and PART 2.

There's an index of all their documents HERE.

 

[kenco]

OK here goes!

System load:-

downstairs........
UFH = 28 000 BTU's

upstairs...........
rads = 35 000 BTU's
210L sealed hot water tank = 55 000 BTU's

I am talking about water pipework sizes, the flow and return to the boiler are both 22mm.

The flow pipe leaves the boiler 0.5m to a Grundfoss 15-60 3 speed pump (currently set on 3), the 0.5m it tee's off via 22mm to the UFH mixing valve/UFH pump/manifold etc. The other leg goes upstairs to the rads/HWT.

The rads all seem to be in 15mm, but I believe some pipework under the floor may be in 22mm!

Hope this is enough info?

Thanks

 

[sterose]

OK here goes!

System load:-

downstairs........
UFH = 28 000 BTU's

upstairs...........
rads = 35 000 BTU's
210L sealed hot water tank = 55 000 BTU's

I am talking about water pipework sizes, the flow and return to the boiler are both 22mm.

The flow pipe leaves the boiler 0.5m to a Grundfoss 15-60 3 speed pump (currently set on 3), the 0.5m it tee's off via 22mm to the UFH mixing valve/UFH pump/manifold etc. The other leg goes upstairs to the rads/HWT.

The rads all seem to be in 15mm, but I believe some pipework under the floor may be in 22mm!

Hope this is enough info?

Thanks

To answer quickly without doing the maths (which I dont know anyway...), 22mm seems adequate for the purpose on pumped pipework.

You may like to know that the bore size of the pumps are usually only 22mm, so increasing pipe size would produce negligable effects.

While I hope this has answered your question, I would suggest that unless you are having problems, that there is probably nothing for you to worry about.

The worst that could happen is probably that, heaven forbid, a radiator or two may not get warm...

 

[taydo]

22mm circuit with 15mm to rads sounds ok why are you doubting the plumber unless of course it doesnt work.

quite often nowdays on pressurised systems the whole lot is run in 15mm apart from a couple of metres to and from the boiler they work perfectly well.

 

[sterose]

...why are you doubting the plumber unless of course it doesnt work.

Absolutely.

quite often nowdays on pressurised systems the whole lot is run in 15mm apart from a couple of metres to and from the boiler they work perfectly well.

Nowadays? I have never seen a system with any other setup than this. Even older gravity systems had 22 or 28mm from the boiler to the tank, and then 22 teed off to a pump for the rads, which was cut down futher when it got to the manifolds.

 

[oilman]

.......they work perfectly well.

The problem is they don't really. The boiler might be interlocked, but the heat usually can't get away fast enough so the boiler keeps operating on its internal thermostat.

22mm will shift 13.5kW , (though I seem to have heard 60,000btu as well)

 

[AdamW]

Thanks to good old Mr Bernoulli's Principle: if you run your 22mm system into some larger bore pipes in order to make work easier for the pump then you will be slowing the water down.

What you really want is the water moving quickly around the circuit but slowly in the rads so it can transfer lots of heat to the radiator fins. Avoids heating up the floorboards (but with underfloor heating that isn't such a big deal for you!)

Using overly-large bore won't yield any advantage PLUS it will mean that your pump is pumping a greater mass of water: your pipes still have to be just as long but having a greater diameter.

 

[kenco]

The reason I ask is that:-

My boiler heat exchanger failed (leak) after 14 months of use!

I contacted Heat Team (Baxi aftersales), they said I would have to pay £170 std charge for them to come out and diagnose the problem (even though I'd told them what was wrong, as my plumber had had a look).

I was told this visit by the Heat team would repair any parts and include labour on everything except the heat exchanger! I made the point that the heat exchanger should not have failed so soon!

3 and a bit weeks later they finally replace the exchanger! (after hassling them most days to get this speeded up) as we have a 8 month old baby.

Then came the BS!

They said possible causes for failure are:-

Scaling found in the exchanger - I was then told that it had to be descaled every 12 months (Baxi technical confirmed this is not true!).

Water turning acidic and attacking exchanger, because of lack of flushing to remove flux after istallation! (I saw commissioning flushing + addition of correct inhibitor with my own eyes. I took water sample and PH tested as I work in a powerstation and it was 7.9, so no probs there.)

Then the relevant bit........ The Heat team 'engineer' stated that the 28mm fitting exiting the boiler would indicate that the 22mm pipe would be too small, and that this would cause overheating in the exchanger due to the heat not being able to get away quick enough!

So I need to prepare a argument that this would not cause the heat exchanger to fail!

They have 'let me off' the £275 cost for the new exchanger, but I am still £170 out of pocket (which they will not refund), due to the initial investigation/fix.

I feel that the exchanger has failed for a reason that is not down to the installation, and could possibly be a manufacturing fault. Surely 2 months out of warranty this should not occur and i should not be £170 worse off for the convenience!

 

[DP]

A cliant had a Baxi Solo that wnet through a HE every 12 months or so. At second heat exchanger, the system was altered to comply with installation instruction. 12 monthe later HE failed again (at the same location as others). More modifications to the installation for the HE to fail end of another 12 months.

The cliant has been very understanding.

At the last failure the boiler was replaced with a Vokera. Keeping fingures crossed.

Above boiler was fitted by a local company. It replaced a Kingfisher in the kitchen. A Worcester I specified and fitted for another cliant fared no better. You name it I have changed it. The back panel (that houses the pipes) was pinholed as well. I had chemically cleansed and inhibited the installation.

My conclusion is that the manufacturers will not want to be backed into a corner with any failure. Look at these and other pages for boilers of a particular type failing regulary. Does the end user get any kickbacks? Not on your Nelly.

As for the 100E, I would have installaed 28mm to first split, would be looking for 11 degrees differential across flow and return, ensure pump on the flow. I also have my reservation about aluminium HE condensers.

 

[kenco]

Thanks, I would be grateful if anyone else had any comments on this thread.

Cheers