boiler outlets on external walls

[benpost]

my grans flat has a driveway with 2 neighbours garage walls either side, one is like this:

the gases come out at head height so you walk right into them

the other neigbours is like this:

is fine

also the first one has caused a rust patch on the block paving:

know if the first outlet is anything to be concerned about, would it pass regulations? if it wouldnt then we will contact the neighbour and suggest having it upgraded.

thanks

[Kevin]

the rust patch is caused by the guard, but what is your problem with the outlet? its height or the rust

[John]

In article , benpost writes

I seem to recall that there was a thread not long ago on the subject of flues into other people's properties. IIRC both these are not allowed unless you have given permission for them to exhaust into your gran's driveway.

[benpost]

well she has a problem with the first one because the gases come out directly in front of you or at you if you walk past it. the other one is higher up and has a 'shield' to stop the gases coming out at the front. if you can see from the pic? as far as i know they can be poisonous, my plumber had trouble finding an outlet at my flat and had to route the flue so it was a big enough distance from any opening windows.

[dennis]

The one with a shield is a conventional balanced flu, the other is probably a fan assisted flu. The shield is to stop strong winds interfering with the boilers burners/pilot.

Flu gases from a properly functioning boiler are not poisonous at all (they do have a lot of CO2 in them which can have a narcotic effect AIUI).

The accidents you hear about with gas appliances are due to lack of ventilation and/or a faulty appliance not mixing enough air with the gas which produces CO which is a poison.

You should be able to stand in the plume all day without anything other than a damp feeling. If burning gas did produce poisonous stuff people with gas hobs would be extinct.

The main reason for the flu is to get rid of the huge amounts of water produced when you burn gas, it would turn your house into a swimming pool if you didn't.

[benpost]

cheers, i'll tell her not to worry about it!

[Terry Fields]

Burning a hydrocarbon gas can result in several products, depending on the ratio of hydrocarbon to oxygen.

Usually, the problem is combustion-flame temperature; in optimal conditions, there would be exactly the right amount of oxygen for the amount of hydrocarbon being delivered. This results in very high flame temperatures, which the materials comprising the system the combustion is taking place in may not be able to tolerate.

Jet engines, rocket motors, car engines, etc, all run 'rich' (more hydrocarbon than is necessary) because even a slight over-enrichment drops the flame-temperature, and eases the demands on the materials the engine is made of.

Unless modern boilers have are designed to run with an excess air supply designed to ensure complete combustion, some other products such as CO will be present in the plume. One way to check this is to see if the exhaust has the characteristic 'gas' smell - a chemical is added to the gas for this purpose. If it's present in the exhaust, then the chances are that complete combustion isn't taking place - so there will be CO in the plume.

Another problem might be the amount of CO2 in the exhaust, accumulating in the passageway on a still day. As soon as the atmosphere contains 4 percent CO2 - possibly not difficult in these circumstances - the body cannot rid itself of its own CO2, the result being a state of hypoxia - one passes out fairly rapidly (BTDTGTTS), with worse consequences if the problem isn't removed.

However, I'm sure there are others on here who know more about the combustion process in modern boilers, and can tell you if I'm talking twaddle.

[dennis]

I'll give you a clue.. the flame should be blue with no white/orange fringes if its working correctly.

Boilers are air and water cooled unlike jet engines (harrier excluded) so they can withstand lean burn quite easily.

[Terry Fields]

hmm...doesn't explain why my neighbour's boiler fumes smell when the wind's in the wrong direction....

[geoff]

In message , Terry Fields writes

Sounds like you have completely wooshed dennis

[dennis]

Find someone else with your level of stupidity and they might play with you.

[Ed Sirett]

There area stack of trace substances in the flue gasses which have a distinct smell that is different to unburnt gas.

Typically flue gasses from a non condensing boiler would be 4.5% CO2, 10% O2, 10% H2O, the rest N2, a little Argon, a few dozen ppm of CO, all of the following are pretty much odourless except for the CO2 which has a slightly sharp odour. The rest are the products of combustion of trace impurities in the gas supply or the stenching agent.

The burner itself more or less operates at the stoichiometric ratio or a bit lean. The flames are hot about 1900C but give off a fair bit of their energy by thermal radiation so that they are quite a bit cooler by the time the come into contact with the heat exchanger.

HTH

[Terry Fields]

Fascinating stuff. Thanks.