Gas condensing and blow off pipe outlets

[markdavies87]

Hi all. I'm new on here and after some advice regarding condensing and blow off outlets. My background is building surveying and I have very little experience on the plumbing side of things so please bear with my poor technical knowledge!

I'm currently surveying housing stock for a social housing provider in preparation for external wall insulation. This involves removing and reinstating lights and many other various items on the external wall of properties as well as extending gas flues.

As regards condensing pipes and blow off pipes - what is the difference? How many of each can a single dwelling have or does this depends on the boiler type/size or number of boilers in the dwelling? From my current knowledge a typical dwelling will only have one condensing pipe outlet, however I'm seeing houses with up to three or maybe four similar looking pipes, some plastic others copper?

Do these so called blow off valves 'spit' water out at force? Is that the reason for them to be re-directed in the direction of the wall?

Finally is there a general minimum length these condensing pipe outlets should protrude from the external wall? From a building surveying side of things I currently find a lot of them only protrude about 15-20mm from the wall and cause staining on the wall below which does look very good, especially on newly rendered dwellings.

Additional information regarding heating sources:
Most of our housing stock have a Worcester 30si combi boiler or a similar but slightly older vaillant model.

N.B. I completed understand the dangers of blocking up gas and boiler vents/pipes. I'm not asking for advice on how to do my job, only information to the above questions which I can interprate myself.

Thanks in advance.

 

[Dean744PiN5]

some of those pipes, will most likely be redundant plastic overflow pipes from old tanks if they have now been converted to combi, could also be overflows to toilet cisterns.

blow off, or safety discharges will normally be small diameter 15mm copper and terminate back to the wall.

condensate pipes will go to drain, such as soil stacks ,waste pipes and gulleys.

but to know for sure you cant complete your survey properly unless you can enter a property and trace the pipes.

 

[Agile]

For a start you should call things by their proper name!

Your "blow off" pipe is really a "pressure release valve vent pipe".

It can discharge boiling water/stead which can injure someone so it is directed bacl to the wall if over 2m above ground ( or in a vandal likely location ) or taken to 150 mm above ground.

Strictly if in a childrens playing area it should have a cage over that 150 mm.

Most external insulation I see just leave an area 300 - 400 mm square around the flue outlet.

I would love external insulation on my house. Whats the cost psm ?

Tony

 

[markdavies87]

Thanks for the reply.

Am I correct in saying that a standard three bedroom dwelling with one typical combi boiler would have only one condensate pipe and only one blow off/safety discharge?

Is there a reason why the blow off terminates back to the wall?

Most condensate pipes on our houses are of the old type which protrude straight out of the wall a few inches into mid-air and drip onto the floor below. As part of the contract we are having these reinstated/redirected to the nearest drain via a new PVC pipe.

I was guessing some of the older plastic (mostly cracked or damaged in some way) were redundant pipes, but like you say it would be best to check where they are coming from.

When plumbers have previously removed water tanks from lofts/old boilers wouldn't it have been industry good practice to remove the plastic overflow pipes?

 

[Dean744PiN5]

Thanks for the reply.



When plumbers have previously removed water tanks from lofts/old boilers wouldn't it have been industry good practice to remove the plastic overflow pipes?

many redundant overflows are left in place, you cant just assume a pipe poking out the wall is the boiler condense. if for example it is an toilet overflow and you directed it to drain, no one would ever know it was overflowing and it would waste water.

i would think it unlikely its a boiler condense pipe just poking out the wall, unless a complete moron installed the boiler.

 

[Terry lambert]

The pressure relief pipe is turned back to the wall so as not to blow scalding water over a person and burn them

 

[markdavies87]

Most external insulation I see just leave an area 300 - 400 mm square around the flue outlet.

I would love external insulation on my house. Whats the cost psm ?

There shouldn't be a gap left around any flues etc if installed correctly as any gaps allow thermal bridging which defeats the object of EWI in the first place. Gas flues should be extended by a GS engineer, vents if required to remain at the property (dependent on type of fire place) extended, and then the EWI should be cut to fit around these protrusions. Any small gaps are usually filled with foam insulation before rendering.

Not sure of the price psm sorry. Typical cost for us is around £7,000+ VAT for a three bed semi (needless to say only three walls, not four like a detached property), but we are doing well over 1000 properties. Privately, i think you are usually talking between £10,000-£15,000. It's a good idea in theory, as long as the people living in the house understand basic condensation and damp issues - if they don't it can cause the house to sweat causing more damp and mould issues than previously which is what we find happens a lot in social housing.

many redundant overflows are left in place, you cant just assume a pipe poking out the wall is the boiler condense. if for example it is an toilet overflow and you directed it to drain, no one would ever know it was overflowing and it would waste water.

i would think it unlikely its a boiler condense pipe just poking out the wall, unless a complete moron installed the boiler.

It isn't the end of the world if we make a mistake regarding the type of pipe at survey stage as the clerk of works will pick these things up t the start of the work and make any corrections, however it is best we are as accurate as possible (within reason - time is of essence) as we want to reduce the number of site instructions on site during the works and all the work is priced before hand from our surveys. i.e. a house will be priced depending on one vent of 6 vents, two waste water pipes totaling 8lm or 5 waste water pipes totaling 20lm... if there are currently four condensing/overflow pipes i'll note it down, if it is found two of these are redundant the clerk or works can change it. It's a bit of a nightmare having to knock each door as we then get tenants bothering us about any other problems they have which you can imagine is a lot!

I think a lot of existing condensate pipes are sticking out of the walls.... I guess that's what happens with social housing when money is tight and some people like to cut corners. However, I know the clerk of works i'm working with is re-directing them.

 

[Biggles..]

Just done a couple of thousand EWI mechanical alterations.

Gas pipes all extended and re sleeved, mounted on 100mm rod and ring then the EWI is installed upto it leaving the pipe proud.
Condense, souls etc are all extended 100mm from the wall face.

Only when flues are obsolete or balanced are they boxed around.

My BIL's a contacts manager, they've done about 10,000, he's now up in Scotland doing a scheme up there.
Cost of a average 3bed semi has increased due to the government and the nervy companies recent arguments over carbon offsets, and the price they buy and sell Carbon. It's circa £15k unfunded.