Advice on Ventilation for Gas Back Boiler

[Brodie]

I have agas fire with a back boiler for the central heating i had gas engineer working on the boiler and he said the regulations regarding ventilation have changed and i am wanting to know how much and where this extra ventilation has to go

 

[mountainman]

Regs are still the same as far as I know.

 

[chris watkins]

Your are right mountainman they have not need updated since the last time, I guess Brodle will have to go back to a Gas SR engineer to have the corrective work carried out, won't they?

 

[jtsplumbing]

Is the ventilation wrong then ? what size back boiler what size vent ? it did change some time back from 4.5cm2 to 5.0cm2 so not a large change may even find that vent is large enough.

 

[Millsy 82]

It did change slightly a few years back so ventilation is either right or wrong anything under 90% is AR where as it used to be something like 70-90% NCS then under that it was AR

 

[mountainman]

Been 5cm for a long time.
Question is I suppose, why is OP asking thus question on a forum when he apparently has a GSR on the case?

 

[pjgas]

mybe the vent has been wrong for some time and the last engineer has picked up on this classic case of customer not believing engineer and thinks he is being ripped off having had other engineers not so competent sevicing his fire back boiler

 

[P J F PLUMBING]

mybe the vent has been wrong for some time and the last engineer has picked up on this classic case of customer not believing engineer and thinks he is being ripped off having had other engineers not so competent sevicing his fire back boiler

As above

 

[topdog]

Until the implementation of BS 5440 part 2 on the 15th January 2000, the GROSS heat input of the Gas was used for the calculation of Ventilation for Gas appliances, We now use the NET value.
Ignoring allowances for adventitious ventilation, an open flued appliance rated at 14kw gross, requires ventilation of 63cm2.
The same open flued appliance would be rated at 12.61kw NET and the ventilation requirements would be 63cm2.
for every Kilo Watt of heat input of an Open flued Natural Gas Appliance, 5 cm2 of ventilation per Kw is required for complete combustion.
To convert your GROSS heat input to Net DIVIDE by 1.11 then times by 5
e.g 14kw divided by 1.11=12.61kw times by 5=63.06 this is 63cm2 vent required.
some take away 7kw from the total kw of appliance this is for Adventitious ventilation then times it by 5.....
the 5 is for 5cm2 for every Kw heat input NET.
e.g 14 kw take away 7 Adventitious air = 7 then times by 5 = 35cm2
But I would prefer to put in the first one and NOT take away the 7,
Because buildings have become more sealed with draft proofing, Insulation and double glazing, so there is not enough air
circulating through the property.
I hope this helps

 

[chris watkins]

yep, well done topdog that should have just about been enough info to confuse the hell out of the OP (don't know what OP stands for, help ??). If he was trying to do the work himself he would have to be Gas trained to make sense of that little lot, well hopefully.

 

[topdog]

yep, well done topdog that should have just about been enough info to confuse the hell out of the OP (don't know what OP stands for, help ??). If he was trying to do the work himself he would have to be Gas trained to make sense of that little lot, well hopefully.

Its simple to work out. Just have to read it...........Just trying to help.......5cm per kw..its not that hard to understand.

 

[Destroyer2813]

Original poster Chris

 

[GrahamM]

Give us a bit info Brodie.
When did you last have appliance looked at? Where is your vent exactly? Do know exactly why the vent is no longer acceptable?

 

[kirkgas]

yep, well done topdog that should have just about been enough info to confuse the hell out of the OP (don't know what OP stands for, help ??). If he was trying to do the work himself he would have to be Gas trained to make sense of that little lot, well hopefully.

OP stands for Original Poster

 

[kirkgas]

Until the implementation of BS 5440 part 2 on the 15th January 2000, the GROSS heat input of the Gas was used for the calculation of Ventilation for Gas appliances, We now use the NET value.
Ignoring allowances for adventitious ventilation, an open flued appliance rated at 14kw gross, requires ventilation of 63cm2.
The same open flued appliance would be rated at 12.61kw NET and the ventilation requirements would be 63cm2.
for every Kilo Watt of heat input of an Open flued Natural Gas Appliance, 5 cm2 of ventilation per Kw is required for complete combustion.
To convert your GROSS heat input to Net DIVIDE by 1.11 then times by 5
e.g 14kw divided by 1.11=12.61kw times by 5=63.06 this is 63cm2 vent required.
some take away 7kw from the total kw of appliance this is for Adventitious ventilation then times it by 5.....
the 5 is for 5cm2 for every Kw heat input NET.
e.g 14 kw take away 7 Adventitious air = 7 then times by 5 = 35cm2
But I would prefer to put in the first one and NOT take away the 7,
Because buildings have become more sealed with draft proofing, Insulation and double glazing, so there is not enough air
circulating through the property.
I hope this helps

topdog, can you clarify that you are saying that you dont take 7 away from net HI for adventitious ventilation? if so then you are wrong, it isnt your decision to alter the regs due to you deciding you want to,
re adventitious ventilation: we often say an appliance under 7kw DOESN'T need ventilation when we should actually be saying PROBABLY wont need ventilation and will be confirmed when i've done a spillage test, due to as you say some properties having had adventitious ventilation (drafts to the punters) reduced by various things happening

 

[huddster]

depends on when house was built as wether you can take off adventitious air- will mainly be a problem for new builds with gas fires

 

[Bernie2]

Hmm! Most ventilation regulation only give you recommended minimum sizes. You are expected to use your own nous to decided whether if the ventilation meets the minimum it is sufficient and everything is okay, you can increase it if you think it is necessary. There are simply to many environmental variables to say the sizes quoted in the regulations are sufficient. Imagine going into a room with regulation size ventilation and all the windows are running with condensation. You would be daft not to investigate the ventilation and up size it if necessary. There is no law to say you cannot exceed regulation sizes.

 

[kirkgas]

depends on when house was built as wether you can take off adventitious air- will mainly be a problem for new builds with gas fires

are you suggesting a vent is based on a build date or just the quality of the actual work (meaning that newer houses are/might/should be better insulated) but what if a new build is drafty or an old house has been insulated,
i use a spillage test on every house with an OF appliance to decide whether i need any ventilation, its a common misnomer that under 7kw doesnt need a vent, what we mean is under 7kw shouldnt need a vent as there is no way of measuring the amount of adventitios ventilation in the room, changes to building regs in 2013 and 2016 regarding making the room more airtight wont ban fitting an OF appliance but to fit one you will have a chimney and maybe a vent which will reduce the airtightness and therefore the room wont comply

 

[topdog]

As I said SOME ENGINEERS TAKE THE SEVEN AWAY, I DONT SO IS IT AN OFFENCE IF I DECIDE TO PLACE 28CM2 EXTRA, I'AM SURE THEY WOULD NOTICE THE EXTRA DRAFT, HAHAHAHAHA
WHAT 28CM2 MORE, IF THIS IS AN OFFENCE THEN I WILL FAIL AS A GAS ENGINEER. BIG LAUGH...................................................
I WOULD SOONER NOT TAKE THE 7KW, A BIT EXTRA AIR VENTILATION REMEMBER MOST HOUSE TODAY ARE DRAFT/LOFT INSULATED.

 

[AWheating]

caps lock stuck?

 

[kirkgas]

As I said SOME ENGINEERS TAKE THE SEVEN AWAY, I DONT SO IS IT AN OFFENCE IF I DECIDE TO PLACE 28CM2 EXTRA, I'AM SURE THEY WOULD NOTICE THE EXTRA DRAFT, HAHAHAHAHA
WHAT 28CM2 MORE, IF THIS IS AN OFFENCE THEN I WILL FAIL AS A GAS ENGINEER. BIG LAUGH...................................................
I WOULD SOONER NOT TAKE THE 7KW, A BIT EXTRA AIR VENTILATION REMEMBER MOST HOUSE TODAY ARE DRAFT/LOFT INSULATED.
KIRKAS SORRY KIRKGAS IS THAT ALL YOU CAN DO IS pig

first things first mr expert i can do anything, dont shout its bad manners, i asked you a question, i wasnt bitching, trust me when i start bitching you will know all about it,
if you dont comply with the regs it looks like a lack of confidence in your super ability, the regs and rules are put in place as guidance in some instances, but if i was checking it i would NEVER over ventilate a property it simply isnt required and can cause unnecessary temp drop in the room and could lead to someone blocking the vent, when i fit a vent i calculate it and place it to minimise the inconvenience to the customer again to hopefully minimise the risk of them blocking it, of course some properties have less adventitious ventilation than others as i stated, thats why i have the skill and confidence in my ability to do and assess the results of a spillage test, if it passes a spillage test there is no need for you to panic a bit and over ventilate, once i have done my calculation and spillage test i will fit the vent and nothing larger, with time and experience you too will build up your confidence and experience and you too will be able to fit the vent required with no need to over ventilate the room to over compensate for your lack of confidence

 

[kirkgas]

As I said SOME ENGINEERS TAKE THE SEVEN AWAY, I DONT SO IS IT AN OFFENCE IF I DECIDE TO PLACE 28CM2 EXTRA, I'AM SURE THEY WOULD NOTICE THE EXTRA DRAFT, HAHAHAHAHA
WHAT 28CM2 MORE, IF THIS IS AN OFFENCE THEN I WILL FAIL AS A GAS ENGINEER. BIG LAUGH...................................................
I WOULD SOONER NOT TAKE THE 7KW, A BIT EXTRA AIR VENTILATION REMEMBER MOST HOUSE TODAY ARE DRAFT/LOFT INSULATED.
KIRKAS SORRY KIRKGAS IS THAT ALL YOU CAN DO IS pig

if you dont take the 7kw off would that not mean fitting an extra 35cm2 rather than 28cm2, obviously im a bit thick and missing something here, do me a favour and explain, sorry if that sounds like bitching, but its not im always eager to learn from my peers

 

[Mike Jackson]

IMO oversizing a vent can lead to problems. The larger the vent the more chance of the customer noticing a draught and the more likely they are to block it. A lot of time and research has gone into working out the ventilation requirements so who are we to make up our own requirements.

Also adventitious ventilation is not ventilation from gaps in doors etc. It is the amount of ventilation created by doors being opened and closed when people leave and enter the room and property.

 

[CES]

IMO OP, If you follow the advice given in the regs and from the "knowledgeable" posters on here, i.e the ones that are actually gas qualified you wont go wrong. The regs are there for a reason and deviation from these will inevitably end up with wrong results, (i.e. wrongly sized vents, customers complaining of drafts, excessive heat loss from the room etc.).

 

[Bernie2]

You can of course oversize vents and cause all kinds of draft problems, if you get it wrong. But you are more likely to starve appliances of air supply with undersized ventilation and all the dangers that implies, than you would with an over sized vent. If in a straight forward case, its a case of taking a chance on people being smothered through a lack of oxygen or feeling a bit cold. There is no competition really. There are many ways to reduce excessive drafts from vents and introduce more air into rooms. You can also get lots of problems with ventilation other than sizing, it is why it is so important to understand the underlying principles of it, hopefully it would enable you to keep people safe. After all that is why gas fitters are called Gas SAFE.

You should not slavishly use the one size fits all of regulation and suppose because you have followed them exactly everything will be okay, you have to work ventilation out accordingly for the places it is required without going below the regulatory minimum requirements. Its not a case of simply saying "I have followed the regs to the letter, so its okay!" it may not be. Gas fitters like everybody else under English Law have a duty of care toward others and part of that is knowing what you are supposedly doing.

I know the ideal is to work things out exactly and that is what one would try to do, as well as site vents properly or use anti draft vents if required and one would not or should not oversize vents without reason. But regulations are what they are and that is usually minimum recommendations,

British Standards are often revised because new things keep coming to light and they find the old regulations where inadequate.
Lets be honest there seems to be a whole industry involved in changing regulations of one kind or another, the Bldg Regs seem to change every week which goes to prove they cannot always be relied on except as a minimum. Exceed the minimum and your okay go under the minimum and your in trouble. Some regulations are not retrospective either, so old ways that were recommended are now substandard and so on and I suppose in some cases perhaps some are now considered dangerous and immediate action is required. So regulation is not a set system of rules but a minimum standard, you as the gas fitter have to decide whether the regulatory minimum is sufficient for the scenario your in.

It is part of a gas fitters job to understand the underlying technology involved in the regulations so they can judge whether to follow them exactly or exceed them if necessary.