plumber competence reprised

[doitall]

That would be my opinion as well without seeing it.

Your obviously spending a few bob, I think owe it to yourself to ensure it will work without problems.

In my opinion you should get the report from your guy then sit down with the builder and discuss what he is doing about it.

 

[achrn]

In my opinion you should get the report from your guy then sit down with the builder and discuss what he is doing about it.

That's what I'm going to be doing, but at the moment I've got two experts one saying "oh yes it does" and one saying "oh no it doesn't". I need to be reasonably confident about what I'm saying going into that 'sit down'.

The builder knows less than me about plumbing (which is where a lot of the aggro arose - his first plumber was saying everything was fine, I was saying it was wrong, the builder spent a long time believing his professional and not his client). Now some of that 'everything is fine' is under floors or in walls of finished, decorated rooms.

any extra costs incurred by you (like additional rent) as a result should be laid at his/their door.

In theory yes, but it's not actually that simple.

I can't just pay a bit more rent and stay put - the owner of the flat already has the next tenant lined up and they are moving in immediately.

If I can't move in to the house the costs are therefore large - hotel bills for my family and storage for all my possessions and double removal costs is probably more than the builder will make on the job (especially as he's had to pay for half the plumbing to be done twice). I don't want to embark on actual legal action to recover costs from the builder, and if I bankrupt him then no-one wins (except the lawyers).

 

[doitall]

There's a way to work out the pipe sizing and both plumbers should know how so it shouldn't be a case of Oh yes it should etc. tell em both to put their calcs on the table.

 

[D_Hailsham]

the flow and return between boiler and cylinder cupboard are currently 22mm, with a length of about 8m each way and seven 90 degree bends and elbows (each way) en route. The boiler is a WB 30 kW GREENSTAR 30 CDi CLASSIC SYSTEM'

That's where the problem lies.

If 22mm pipe is used and assuming a 20C differential, the pressure loss (head) in the pipes between boiler and cylinder cupboard would be approx 2m. Using 28mm pipe it would be approx 0.4m.

The spec for the OP's boiler says that the available head from the pump is 2m. So, if 22mm pipe is used, there would be nothing left to circulate the water round the radiators. If 28mm pipe is used there would be 1.6m available.

This assumes the boiler is running at its maximum 30kW output.

 

[bolshy]

I don't want to embark on actual legal action to recover costs from the builder, and if I bankrupt him then no-one wins (except the lawyers).

You will perhaps have to compromise. It's clearly in your interests to get the house finished, but as already said, your system has to work properly. If I was the installer, I wouldn't be letting the builder carry out his final finishing in any room until I was certain the system was working correctly and meets the building requirements. Half the battle is to specify properly in the first place and follow the manufacturers instructions.
The builder should be recovering some of the plumbing costs from his own plumber, surely? A lot of the blame lies squarely with his plumber. Although I suspect the builder knows more about plumbing than he is letting on - there are plenty of them who install pipework in my experience.


Paying good money for something that doesn't work properly, or works poorly is something I suspect your tradesmen wouldn't do in their homes.
You're going to have to take the bull by the horns and thrash out a solution.
Perhaps the best compromise would be that the builder provides labour free of charge to put things right, and perhaps you provide materials at cost. I don't know. Sticky situation.

 

[Biggles..]

So you sacked one plumber for his incompetence or not! But now your going to live with certain safety aspects that you know to be substandard.....nice customer.

22mm copper is about 26kw@1m/s

 

[achrn]

Thanks for the several helpful comments.

Picking up a few into one place:

I had already said I wanted to see calculations justifying the assertion that 22mm primary flow and return was appropriate before that suggestion was made here. It's useful confirmation that this is an appropriate thing to ask for.

I've done my own, as it happens, and by simple physics I conclude that if I've got 30kW going into a water flow and raising the temperature 20C the flow is 0.36 kg/sec. I've assumed each elbow is equivalent to 0.6m of straight pipe (this is the step I simply don't know if it's valid - I found that figure on the web). My 16m of pipe is therefore equivalent to 24.4m straight. From the NA to BSEN12828 0.36kg/s in 22mm pipe is a pressure drop of 668 Pa/m, so I use up 16.3 kPa or 1.6m of head. That ties up with the statement that it's about 2m (thanks for that). (My calcs for 28mm give me 0.5m so matches well teh 0.4m posted.)

This gives me the reassurance to tackle the new plumber. Thank you.

Regarding sequencing the finishes - that's what the builder did, that's the builder's problem (costs wise). The source of the problem is that the installer (who has subsequently been proven to be incompetent) did tell the builder it was finished and everything was fine. The builder believed him, and didn't believe me when I said it wasn't.

The costs of the re-work are not being met by me. I don't much care whether the builder recovers it from his original plumber or not. What does matter to me, however, is if the works over-run. Then I get significant costs and will be trying to recover them from the builder (or withholding payment and then justifying doing so). That probably requires 'going legal' and I want to avoid that.

 

[doitall]

You are raising the temperature say 50-60c, the 20c is the differential between the flow and return, 60/40 for example.

 

[achrn]

You are raising the temperature say 50-60c, the 20c is the differential between the flow and return, 60/40 for example.

Yes, I know - so when everything is balanced the return water comes into the boiler at 40C and is raised 20C to 60C by 30kW of input, so the flow must be 0.36 kg/s. I'm examining the steady state, not on the on-from-cold case.

That's trivial physics - specific heat of liquid water at about atmospheric pressure is about 4.2 kJ/kg/K.

I can do physics. It's plumbing I don't know about.

 

[mehran]

achrn, forget for a sec you have a 30kw boiler. what is the heatloss of your house? what can your rads even output?

upping the primary flow and return to 28mm may gain you nothing other than hassle.

 

[Agile]

Yes, I know - so when everything is balanced the return water comes into the boiler at 40C and is raised 20C to 60C by 30kW of input, so the flow must be 0.36 kg/s.

I can do physics. It's plumbing I don't know about.

Since water conveniently weighs about 1 kg for a litre then you can put 0.36 litres/sec as a flow rate.

We like to use a flow rate per minute so thats easy to multiply by 60.

A friend had a new kitchen fitted and after a week there was a bad leak which spoilt the floor. Being a solicitor he and his wife moved into a hotel for six weeks at the builder's expense!

At least your builder will not use sub-standard plumbers again!

Are you really not able to move in whilst these minor improvements are being made?

Tony

 

[achrn]

Yes, I know - so when everything is balanced the return water comes into the boiler at 40C and is raised 20C to 60C by 30kW of input, so the flow must be 0.36 kg/s.

Since water conveniently weighs about 1 kg for a litre then you can put 0.36 litres/sec as a flow rate.

I left it in kg/s because the flow figures table in BS EN 12828 has flow in kg/s, so assumed that's what designers of heating systems used. The Worcester Bosch instructions say that where no specific instruction is given, reference should be made to (among other things) EN 12828.

 

[achrn]

achrn, forget for a sec you have a 30kw boiler. what is the heatloss of your house? what can your rads even output?

If I add up radiator and heater outputs (I've guessed for the three towel rails, I've got the manufacturers figures for the rest) I get 23.3 kW.

The cylinder has a 20.5 kW coil.

Do you size on adding these up? In that case my system can more than consume the boiler capacity.

For the heatloss of my house, I've done Energy Saving Trust 'whole house method', but rather than use their window factor I've added up the area of walls, floors, roofs, windows etc and used the heat loss figures they quote in the workings. I did it this way because I have a mix of new insulated cavity walls and original solid 9" brick, and some pitched and some flat roof, and my ground and first floors are dramatically different plan areas. I get 18.2kW (with 2kW allowed for water).

I've also done the Wickes 'choose your radiators leaflet' method, which seems to just be 45 W per cubic metre of room, less 25% if it's upstairs and that gives me 20.3 kW, so so much for the long calculation.

So I have a 30kW boiler, a 20.5kW cylinder coil, 23.3kW of radiators and around 20kW of heat loss (depending on method used for calculation).

In that case, specifying the pipes so I can get full power out of the boiler doesn't look completely unreasonable to me, but I'd welcome comments from someone that knows what they are doing.

 

[shambolic]

Most manufacturers state, well we do, that a boiler output of over 18kw should have 28mm primaries from boiler.

 

[Dan Robinson]

I won't say a word about your employer's heat exchanges Shambo .