flue positions on combi boilers

[rongagain]

My daughter's flat is on the 4th floor and she is in need of a new combi boiler. The flue exits through the wall.
My questions are, can the boiler flue be installed from inside the flat as it is about 40ft up from the outside.
Also does the position of the flue as it exits the boiler change from make to make. She currently has a Myson Midas Si.

Thank you very much for any help/advice. Anything else she needs to consider?

btw she has been quoted £1350 + vat for an ideal 30 boiler fitted IF the flue can be done from inside or 1799 = vat if flue needs outside work, the extra is for a 'cherry picker'. What do you think?

Thanks

 

[armourer]

The installer will need outside access as after the flue is cut through the wall he will have to seal it (outside)to stop any fumes getting into the cavity of the property, where it may be able to find its way either into her flat or someone elses.

The price seems cheap.

 

[Solo Heating]

Hi ronagain,

Combi boiler flues can usually be installed from inside but it does depend on the make of boiler. The only determining factor is whether the installer can seal the gap between the outside wall and the flue.

The process of making the hole (if not using the existing hole), passing the main body of the flue through the hole and fitting it to the boiler can all be done from the inside. If the flue can be pushed through the hole with its external seal put on to it in advance, then all's well and good - it just means the installer will need to ensure the connection inside is as it should be and the external seal fits snugly in place when viewed from the outside. Some boiler flues make this easy because the seal is flexible, some are rigid so can't be passed through the hole and therefore must be attached externally. For good measure, it is always a good idea to muck round the external gap but the manufacturers often don't specify this so using the seal they supply is fine (as long as it fits tightly to the wall - it's the installers job to ensure this!).

I'd say the prices given are fair to cheap. Don't forget the issue of drainage for the condensate from the new boiler. Ideally it should run to an internal drain such as under a sink or to a washing machine drain. Also, if the boiler's dimensions and flue position are slightly different to the existing boiler then using the existing flue will change the position of the boiler on the wall (hopefully not by much).

cheers,

Ben

 

[AWheating]

the cowl supplied with the flue is not the correct method of sealing to brickwork, it is neither water or air tight, so although it can be pushed through from inside and pulled into position you will still need to some way produce a seal between brickwork. It may well be possible to do this from inside by making a larger hole inside then out to gain access or possible even the use of an expanding sealant.

 

[mfgs]

The covers supplied with the flues are purely decorative as far as I am aware, to cover the making good of the flue hole. They arent an approved method of sealing the gap around the flue.

As said above, you will either need to make a bigger hole inside to seal the outer hole and then have alot of making good on the inside. Or its a job from the outside off some scaffolding or a cherry picker

 

[rongagain]

Thanks for the fast responses guys.
So the important bit is ensuring there isn't a gap around the outside of the flue (externally) by the sounds of it. The flats are 20 years old and good brickwork, still needs sealing I know. Can a flexible seal be 'loaded' with sealant pushed through and pulled back?

The price quoted of £449 + vat for a cherry picker for say 15/30 minutes is hard to take........ Do any of you have to work on blocks of flats? What happens in higher buildings? If the flats are very high what then?

I really appreciate your experience and helpful advice. I am looking for a reasonable cost, but ultimately it will be done correctly, I don't want any cut corners safety wise.

Thanks again

 

[Barry98]

where is she located ?

 

[AWheating]

you may be able to seal it with an fire rated expanding foam but i would seek advise from boiler manufacture to make sure the flue material is suitable and will not react to any chemical in the foam. you can also get cement based tubes that will fit a mastic gun like the cement use on pre cast flues, make sure what you use can be used externally.

 

[Solo Heating]

I have spoken to a few manufactures about the outer seal and they've all agreed that it is an acceptable way of sealing the gap as long as it is tight. I think Alpha still include details on fixing flues from the inside using the method I described above but I might be wrong. Vertical terminals don't require any extra sealant so I believe the manufacturers external seal is deemed acceptable on horizontal flues for the same reason. Don't forget the outer leaf of any wall isn't water tight anyway, which is why there is a cavity, so it's purely to keep out wind and flue gases.

That said, it is advisable to seal the gap for piece of mind. It also helps keep the flue in place.

Cheers,

Ben

 

[GrahamM]

I have spoken to a few manufactures about the outer seal and they've all agreed that it is an acceptable way of sealing the gap as long as it is tight. I think Alpha still include details on fixing flues from the inside using the method I described above but I might be wrong. Vertical terminals don't require any extra sealant so I believe the manufacturers external seal is deemed acceptable on horizontal flues for the same reason. Don't forget the outer leaf of any wall isn't water tight anyway, which is why there is a cavity, so it's purely to keep out wind and flue gases.

That said, it is advisable to seal the gap for piece of mind. It also helps keep the flue in place.

Cheers,

Ben

Firstly, as others have said, not to seal the gap round the flue is just poor practice. Most of the Manufacturers state a distance of 300mm from the flue to a vent/opening and you think it is acceptable to leave a 10mm or so opening all the way round the flue. Does not add up. Show me a rubber/plastic cosmetic flue seal that will make a seal to a roughcast wall preventing combustion gasses from being drawn back in.
Not to mention how many condensing boiler flues I have rectified as they have dropped down within the flue hole as they have not been adequately sealed/supported by a bit of good old sand and cement.

 

[Solo Heating]

Firstly, as others have said, not to seal the gap round the flue is just poor practice. Most of the Manufacturers state a distance of 300mm from the flue to a vent/opening and you think it is acceptable to leave a 10mm or so opening all the way round the flue. Does not add up. Show me a rubber/plastic cosmetic flue seal that will make a seal to a roughcast wall preventing combustion gasses from being drawn back in.
Not to mention how many condensing boiler flues I have rectified as they have dropped down within the flue hole as they have not been adequately sealed/supported by a bit of good old sand and cement.

Hi,

I did say in my first post that sealing the gap is best but if you do enquire with the manufacturers they will tell you it is acceptable to use the rubber seal they provide. I nearly always install Viessmann but used to fit Vaillant and Alpha. All three use similar seals and they are perfectly adequate for keeping out flue gases which I'd be happy to show you. Viessman's flue installation instructions do not show any need to seal that gap because the seal is so tight on the flue and extends 75-100mm over the brickwork. Alpha certainly used to include instructions for fitting the external seal from the inside by placing it onto the flue and pushing it through the hole; this was for flues which couldn't be accessed from outside which is exactly what the thread is about.

I appreciate that it's not best practice but the manufacturers instructions can override the Gas Regulations and so it is acceptable under certain conditions such as this.

 

[marleyco]

when in worked for a certain council gas team, pushing through and pulling back is the way it was done. 4 storeys is high but some i worked in alot higher. not saying its the right way to do it, but there was no way they would put the expence of scaffold or cherry picker against the job, its from their pocket.

 

[rongagain]

Firstly, as others have said, not to seal the gap round the flue is just poor practice. Most of the Manufacturers state a distance of 300mm from the flue to a vent/opening and you think it is acceptable to leave a 10mm or so opening all the way round the flue. Does not add up. Show me a rubber/plastic cosmetic flue seal that will make a seal to a roughcast wall preventing combustion gasses from being drawn back in.
Not to mention how many condensing boiler flues I have rectified as they have dropped down within the flue hole as they have not been adequately sealed/supported by a bit of good old sand and cement.

Thank you for the advice. Although I didn't think that there could be " ...a 10mm or so opening all the way round..." if a seal was used with a sealant? In order to get a bit of sand and cement round the flue, as good an idea as that is, will cost (as quoted) £540. Hence my appeal for an alternative good practice solution when working 40 ft up. As I asked earlier what about very high blocks of flats much higher than 40ft?

I am told scaffold would be more expensive? The 'cherry picker' price seem about right?

Thanks again

 

[armourer]

I would say its not your decision anyway it will be up to the installation engineer on site, how he is going to do the job.
He is the one that is risking his career and signing the boiler off as being safe and if he is not happy to do it that way the last thing he would want is a customer telling him how to do his job.
Sorry if that came across a bit harsh but thats what our qualifications and college time is for.

You are of course within your rights to get advise from anyone you like but the trouble with internet forums is that it is no replacement for actually seeing the job.
I hope you get it sorted one way or the other.

 

[tamz]

It has always been accepted practice to fit flues from inside sealed using the ring supplied. Most (but not all) manus allow it. You just need to drill a big enough hole to pass the collar through with the flue, pass it through and pull back to seal. It is good practice when doing this to seal the inside hole.

From some mi's
Worcester
B If a 100 mm diameter flue is to be used, a 125 mm
diameter hole is required. However, if using the
weather sealing collar by pushing it through from
inside the property, then a 150 mm diameter hole is
required to accommodate this.
Vaillant
• Push the air/flue duct assembly
(1) including the flexible external
seal through the wall until the
seal clears the outside face of the
wall and pull air/flue duct back
towards the boiler until the
external seal touches the outside
wall.
• Ensure that the air/flue duct (1) is
centred in the hole and the
terminal is correctly positioned
with the inlet grille at the bottom.
Alpha
4. Pass the flue assembly through the wall (from inside or outside).
Note: Internal fitting - If there is no access to make good the outside wall, locate the flue sealing collar onto the outer duct
of the flue immediately before the terminal grille onto the location provided. Push the flue assembly through the 130 mm flue
hole, so that the collar completely passes through the wall. Then pull the flue assembly back into the correct position. Visually
check that the collar is sealing the outside wall and that it is not restricting any of the openings of the flue terminal.

Common sense has to be used in these situations. What if it was on the 10th floor, well beyond the reach of any cherry picker and astronomical scaffold costs if it was to be done that way.
"Sorry pal gas is out the question. You will need to fit electric or learn to absail with a handfull of compo"
I don't think so.

 

[rongagain]

I would say its not your decision anyway it will be up to the installation engineer on site, how he is going to do the job.
He is the one that is risking his career and signing the boiler off as being safe and if he is not happy to do it that way the last thing he would want is a customer telling him how to do his job.
Sorry if that came across a bit harsh but thats what our qualifications and college time is for.

You are of course within your rights to get advise from anyone you like but the trouble with internet forums is that it is no replacement for actually seeing the job.
I hope you get it sorted one way or the other.

Not harsh at all. You are right of course, my questioning was based on the fact the first quote seemed unsure whether it could be done from the inside, hence my 'interest' in options. I wouldn't attempt to tell someone how to do their job, but I could carefully suggest ideas if from other experienced and qualified people, no body has experienced everything about their trade.

I am getting further quotes but you all have given me some good advice.