Condensing combi and size of gas supply pipe

[Shiveringinsuffolk]

I have a Potterton Puma 100E combi boiler that has given up the ghost and I've been getting quotes to replace it. My home has 3 bedrooms and 1 bathroom ( 8 rads and Mira excel shower).

I have had about 6 quotes - boilers recommended have included Baxi Duo Tec 28E or 33He, Vaillant Eco-tec 837, Worcester Greenstar 30 CDI).

My concern is that some (but not all) of the engineers have expressed concern that my gas supply pipe may not be big enough for one of the new condensing boilers. The gas pipe is 22mm, but there is a fair run from boiler to metre (about 14 metres with about 6 or 7 turns). There is also a gas fire and gas oven/hob coming off the supply. One guy thought it could be a real problem, a couple of others mentioned it as a slight possibility that it could cause a problem.

I have been told that the gas pipe may need upgrading to 28mm. I won't go into detail but it is really quite impractical to run a new pipe with the boiler in the same location as it is now.

My question is, are these concerns unfounded or perhaps unlikely to actually be a problem? Also, would installing a slighly smaller/less powerful boiler with a lower water rate flow help? The water flow rate of my existing boiler is fine (believe it is about 11 litres per minute).

I'd rather accept a slightly lower water flow rate if it means I don't have to replace the gas pipe, which would be an obsolute nightmare in my house.

I would appreciate your advice and thoughts.

 

[Baxi-Remeha]

a gas pipe size calculation can be done to tell if the pipe will supply enough gas to the new appliance.

a less powerful boiler will require less gas, therefore the pipe size you have at the min might be sufficient.

 

[landyandy]

A 37 Kw boiler for eg. (ecoTec 837) will almost certainly need an element of gas pipework larger than 22mm.

The correct pipe size is very important and will only lead to problems, when commissioning, if not calculated correctly.

Difficult without being there, but the engineers mentioning possibly upgrading the size seem to be giving good advice.

Andy.

 

[Temprise]

Sounds like you are getting good advice.

I have worked for two manufacterers and one of the most common call outs for combi's with poor hot water and heating performance is due to undersized pipework.

Regards.

 

[Shiveringinsuffolk]

Thanks for the replies.

Should be fitter be able to give me a pretty definate answer before installing the boiler? The guys that have raised concerns say it 'might' be a problem, but indicate that they will not really know until after the boiler is installed.

given that rerunning the gas pipe is such a nightmare in my house, I really need to know beforehand if I'm going to have a problem (the first 3 metres is behind a recently instaled fitted kitchen, then the other 11 metres is in the concrete floor - to run it surface mounted I'd ned to run the pipe across 2 doorways and an inglenook fire place).

How is the gas pressure measured and the pipe width calculated? Can this be done before installation takes place? What do you think would be the smallest size boiler I could get away with?

 

[dextrous]

Once the pressure is measured at the meter, then the length of pipe, number of bends, other gas appliances etc is taken into account, since each of these will affect the pressure at the boiler end of the pipe. Once this pressure loss is known then the appropriate pipe size can be determined.

An RGI will know how to do this prior to installation

 

[Tipper]

Whilst you will need a gas man to do the real calcs for you there is this nomogram which helps to give a view of the pressure drop on the pipe for a given length plus bends, etc, so you can get a level of confidence on what they are saying.

But no susbstitute for the real thing as they say!

http://www.slumberlands.freeserve.co.uk/gasflow.htm

 

[gas4you]

Any of those boilers mentioned will require the gas pipe to be replaced with 28mm up to calculated point, especially with other appliances teed off this pipe.

Can't see why they can't be definate about it. One look usually tells the installer wheter it is going to need it or not and the calculations are just to determine the exact requirements.

 

[Agile]

Anyone who mentions the gas pipe size at least has an appreciation of whats involved in correctly fitting a boiler.

What concerns me more is that you have already had six people out to give free quotes when only one is going to get the job.

Say each travelling and visit took them 2 hours then 10 hours of wasted time has been involved.

Thats why we dont go to give free quotes as it would just increase overheads which have to be covered by our customers. Instead we ask a lot of questions and give a budgetary quote on the phone. If thats acceptable we go to confirm it but the cost rarely changes.

If only some gas supply upgrading is required then doing this at the meter where there are several bends and at the boiler will sometimes suffice.

If the existing boiler can be made to work then I measure the actual pipe loss which is more informative.

Tony

 

[Shiveringinsuffolk]

Agile, you obviously feel that 6 quotes is excessive and that I've been wasting peoples time and money. I started with 3 quotes but the prices and advice given varied a great deal, so I decided to get another 3. If the advice and prices quoted by the first 3 guys hadn't varied so much I wouldn't have got another 3. A site visit was deemed neccessary by them, not me - afteral, they are the fiters with the knowledge and experience, not me.

All 6 fitters asked me where the gas meter was, two of them looked at the meter, none of them took a pressure reading. 3 didn't mention that there might be a problem at all, one said it might be a problem with some more powerful boilers, but then said "we should be okay", one said "leave it with me" then rang back and said it would be okay. One seemed more concerned than the others and went on to explain that if he had to upgrade the gas pipe it would involve extra costs. He said he couldn't be sure until after he had installed the boiler. I couldn't get him to commit himself to how likely there was to be a problem. Ironically, he was the guy I was most impressed with, apart from him sitting on the fence about the gas pipe.

I just don't want to shell out over two grand on a new boiler and find it doesn't work because of the gas supply. Although some of the guys have mentioned it might be a problem, I was hoping for more than a 'definate possible might be' before commiting myself.

I know nothing can be 100% definate, but I was hoping for a 'highly probable' one way or the other, or 50-50 - just some indication of how likely there is to be a problem.

 

[gas4you]

Although I agree 6 quotes is rather excessive, it comes with the territory to have to go out on site to prepare an accurate and guaranteed quote.

Usually I will not give any price info without visiting the proposed job.

 

[gas4you]

I would personally only look at the quotes of those who mentioned the gas pipe size.

In terms of percentages, I would say it will be 80% certain you will need a gas pipe upgrade.

 

[nogoodatfaultfinding]

I would have to respctfully disagree and say that for a 28HE or even a 33HE you would get away with the 22mm pipe.
I have done some big runs before now with 2 x Gas Fires an Oven and a Hob coming off in between where 22 has been more than enough.

 

[Agile]

One seemed more concerned than the others and went on to explain that if he had to upgrade the gas pipe it would involve extra costs. He said he couldn't be sure until after he had installed the boiler. I couldn't get him to commit himself to how likely there was to be a problem. Ironically, he was the guy I was most impressed with, apart from him sitting on the fence about the gas pipe.

Thats the totally correct approach !

He does not want to lumber you with additional costs if they were not necessary.

The pressure loss can be calculated but the measured value can be some way different, thats higher loss.

I appreciate that you were unimpressed by some of those who came round. ALL should have looked at the gas meter and mentioned that some upgrading may be necessary.

Thats the one guy you should be seriously be considering.

All the boilers will still work on the existing gas pipe but it will not meet the standards we should work to.

Cowboys dont mention this to you and get away giving a lower quote because they are not going to upgrade the gas.

Tony

 

[nogoodatfaultfinding]

One seemed more concerned than the others and went on to explain that if he had to upgrade the gas pipe it would involve extra costs. He said he couldn't be sure until after he had installed the boiler. I couldn't get him to commit himself to how likely there was to be a problem. Ironically, he was the guy I was most impressed with, apart from him sitting on the fence about the gas pipe.

Thats the totally correct approach !

He does not want to lumber you with additional costs if they were not necessary.

The pressure loss can be calculated but the measured value can be some way different, thats higher loss.

I appreciate that you were unimpressed by some of those who came round. ALL should have looked at the gas meter and mentioned that some upgrading may be necessary.

Thats the one guy you should be seriously be considering.

All the boilers will still work on the existing gas pipe but it will not meet the standards we should work to.

Cowboys dont mention this to you and get away giving a lower quote because they are not going to upgrade the gas.

Tony

Please Tony that is rather unfair.

Not all Gas supplies need upgrading and most boilers of the type we are talking will work more than adequate of a 22mm supply(28HE - 33HE) and is why they come with that size conection.

Dont paint everyone as a cowboy because they all dont feel it needs an upgraded supply.