Combi's and Approved Document L1

[mmccar]

I had British Gas around last week to see if I could replace my existing wall mounted boiler in the kitchen with a combi, allowing me to ditch the ShowerMax in the bathroom. They informed me that as of April this year, all new Combi's must be condensing, which require a

22mm feed. Unfortunately, my existing boiler has a 15mm feed, the 22mm feed into the house, post meter, drops into the concrete floor in the garage and at some stage before popping out the wall in the kitchen changes to 15mm.

So it looks like I have two options, either:

a) Replace boiler in same position - will require digging up of concrete ground floor to locate the start of the 15mm pipe.

b) Move boiler to garage - will require lifting of upstairs' floor to redirect pipe work from bathroom.

I believe both options will require a vertical extended flue over 2m, as distance of the existing/new horizontal flue terminal to neighbouring boundary is/would be 1000 would this mean I would qualify for a non-condensing boiler?

I can't believe that the government expects anyone requiring a new boiler to have to replace it with a condensing boiler at any 'monetary cost' because the 'assessment cost' is below 1000.

To add to the confusion, the British Gas guy was unaware of the new

2=2E5m minimum distance rule and still believed it to by 0.6m, he even checked the documentation on his laptop, which he informed me, made no reference to the new distance. This is a little worrying considering British Gas have been fitting condensing boilers under the new regulations for several months now. He also said they could fit a plume divertor terminal if it was going to be an issue, however, I believe this would still be too close to my property boundary?

Any expert advice would be greatly appreciated as I am looking at having to layout =A33500 if I am forced to go down the condensing combi route.

[Owain]

AIUI your existing boiler is not a combi? I don't know what a Showermax is.

The larger gas feed is required because the new boiler is a combi and has to provide instantaneous hot water, not because it's condensing.

If you think about it, a condensing boiler would require a *smaller* has feed for the same output, because it's more efficient.

New boilers must usually be condensing, but they don't have to be combi.

Owain

[Andrew Gabriel]

There's a mistake here. The larger pipe is because it's a combi, and nothing to do with it being condensing.

[Andy]

22mm feed. Unfortunately, my existing boiler has a 15mm feed, the 22mm feed into the house, post meter, drops into the concrete floor in the garage and at some stage before popping out the wall in the kitchen changes to 15mm.

So it looks like I have two options, either:

a) Replace boiler in same position - will require digging up of concrete ground floor to locate the start of the 15mm pipe.

b) Move boiler to garage - will require lifting of upstairs' floor to redirect pipe work from bathroom.

I believe both options will require a vertical extended flue over 2m, as distance of the existing/new horizontal flue terminal to neighbouring boundary is/would be 1000 would this mean I would qualify for a non-condensing boiler?

I can't believe that the government expects anyone requiring a new boiler to have to replace it with a condensing boiler at any 'monetary cost' because the 'assessment cost' is below 1000.

To add to the confusion, the British Gas guy was unaware of the new

2.5m minimum distance rule and still believed it to by 0.6m, he even checked the documentation on his laptop, which he informed me, made no reference to the new distance. This is a little worrying considering British Gas have been fitting condensing boilers under the new regulations for several months now. He also said they could fit a plume divertor terminal if it was going to be an issue, however, I believe this would still be too close to my property boundary?

Any expert advice would be greatly appreciated as I am looking at having to layout £3500 if I am forced to go down the condensing combi route.

Not too sure about the distance of the flue to the boundary: the problem with condensing combis is that they put out large clouds of steam on some days as the exhaust is so cool, and that would constitute a nuisance to a neighbour. If the BG man can deflect the existing flue upward perhaps this will be ok, AKAIK the issue of distance to boundary oly really applies for sideways facing flues. You can dig the relevant regulations up on the web, some of the combi manufacturers have them as .pdf files on their websites. As for the gas pipe, then if you are fitting a combi that is much more powerful than your existing boiler ( a typical combi might be 28kW, I don't know what power your existing boiler is ), then the feed pipe by rule of thumb needs to be

22mm to within 1metre of the combi, then 15mm is allowable for the last meter. The reason is the pressure drop will be far too great if you use 15mm pipe for the combi to work within specification. There are calculator websites available on the web to help you work out the actual pressure drop, but certainly 15mm will not do.

Andy.

[mmccar]

Thanks everyone for your replies.

Andy, so if my 22mm pipe drops to 15mm within 1m of the boiler I may be ok - I'm thinking the pipe change may be in the wall as opposed to the under floor - any ideas what the standard practice is, is it even permissible to lay concreate on a 15mm pipe? Can I get a Corgi engineer measure the pressure to see if the 15mm pipe will suffice?

[mmccar]

Thanks everyone for your replies.

Andy, so if my 22mm pipe drops to 15mm within 1m of the boiler I may be ok - I'm thinking the pipe change may be in the wall as opposed to under the floor - any ideas what the standard practice is, is it even permissible to lay concreate on a 15mm pipe? Can I get a Corgi engineer to measure the pressure to see if the 15mm pipe will suffice?

[Andy Hall]

Not quite. All new gas boilers must be condensing, unless you qualify under the points system not to have one.

You are going to have to do something about the gas supply anyway. the issue is the gas rate required by the combi - it is not an issue of condensing or not. Perhaps it is possible to do this with running a new pipe other than through the floor?

Option a) would apply since it is possible to install in the existing position. For the purpose of the assessment, the lowest scored option is used. If you choose to re-site, that is your choice - you can't use it to increase the points as you suggest in option (b)

It doesn't make any difference.

We live in a nanny state. This is what people voted for.

He is looking at the safety requirement which is 0.6m. The other is only to avoid potential nuisance to the neighbour from a possible plume. With a very long flue, it is quite likely that there would not be significant pluming anyway because much of the water vapour would condense and run back to the boiler.

Two things here.

Look at other suppliers as well as BG and you will discover that they are charging much more than most independent heating engineers - often up to twice as much.

You could look at a boiler which will take twin plastic flues. Quite a number have this as an option and they are implemented using 50mm muPVC high temperature waste pipe. This gives a much neater and cheaper solution for long runs, especially if you have to have some gymnastics with the routing.

It should be possible to do this for under £2000. If you choose an independent installer. Much of the work will be with running a new gas service which you'll need anyway and a new flue. The difference in boiler cost is not going to be great in the equation, so you might as well have a condensing product and save on gas as well. Roughly speaking the comparison is between 80% vs 90% seasonal efficiency so you should be able to achieve a payback within the lifetime of the boiler.

[Andy Hall]

This is a bit difficult to do since the existing boiler is running at a lower gas rate than the combi would. The point would be the pressure drop from meter to boiler which must be no more than 1mB. However that has to be measured under load conditions.

You can calculate based on the guidelines at

if the 15mm run is about 1m, it should be OK as long as the rest is 22mm.

It is common to use iron pipe in concrete, but the internal diameter is only slightly more than 15mm copper, unfortunately.

Perhaps you could excavate near the boiler and see what the pipe is?

Copper pipe can be run in concrete provided that it is sleeved in some way to prevent corrosion of the copper - a material issue not a size one.

[John Rumm]

To be sure, you wil need to do the sums. The first thing to find out is the maximum input gas rate of the boiler (it will be in the handbook, which you can download from the makers web site). Then use the CDA document that Andy posted a link to to see if your existing pipework will do the job.

[John Rumm]

One commonly used solution these days is to run the gas pipe round the

*outside* of the house, and just come back in near the boiler.

The longest "throw" of visble steam from the flue on my boiler (installed on the side of the house - pointing at the neighbours property some 2.2m away), is at most 400mm. So it does not even get as far as the boundary.

[mmccar]

Thank you all for your replies, got an independent installer coming around next week, if we can't find distance of 22mm from boiler will suggest running pipe round the outside of the house. :-)