Flue Exit - Height From Ground

[MrFrisbee]

I am about to have a new combi fitted.

Current flue is 20cm above ground level as it emerges from the property.

Regulations specify this must be 30cm now but we have no height internally to raise the flue at all and the flue cannot be turned outside (as it is an internal flue only).

So, we either have to box the flue in outside and raise it (so it is not technially "outside) or I can have the ground below the flue lowered (as it has been excavated anyway for some drain changes. We can infill the hole but leave a trough around the flue exit point so that it is 30cm above the lower ground level.

Do you think this is an acceptable solution?

Thanks,

Charles.

 

[namsag]

Yes it must be 300mm but if its not it will only be classed as
Not to Current Standard. And can be left

 

[kevindgas]

Current flue is 20cm above ground level as it emerges from the property.

what ? do you live underground ? please explain

 

[bengasman]

....and the flue cannot be turned outside (as it is an internal flue only).

That is somewhat unlikely

So, we either have to box the flue in outside and raise it (so it is not technially "outside)

That is not an option

or I can have the ground below the flue lowered (as it has been excavated anyway for some drain changes. We can infill the hole but leave a trough around the flue exit point so that it is 30cm above the lower ground level.

Do you think this is an acceptable solution?

Not really. If the flue is in a trough, the fumes will mix with the air used for combustion in an unpredictable way.

Which boiler is going in?

 

[bengasman]

what ? do you live underground ? please explain

Basement flat probably, quite common in London.

 

[twgas]

Not really. If the flue is in a trough, the fumes will mix with the air used for combustion in an unpredictable way.

a plume management kit would solve that.

 

[MrFrisbee]

Thanks for the quick replies. Here are some quick answers.

1. No, I do not live underground, the boiler does.
2. Plume management kit will be used to lift plume 2metres etc.
3. here is a picture of the current situation...

 

[bengasman]

It would, but it still would not bring the flue at the required height.
I know that WB reduce the required 300mm from an opening to 150 with plume management, but I haven't heard anything about corners and floor.



Brings up another interesting point: the basket has to go around the flue-terminal, and technically speaking (as in "corgi-technical") the flue is the coaxial bit. afaik

Lowering or sloping the outside ground level would be a way.
Maybe a twin flue model.

 

[bengasman]

Creative bit of construction.
Where is your prv outlet?

 

[MrFrisbee]

It would, but it still would not bring the flue at the required height.
I know that WB reduce the required 300mm from an opening to 150 with plume management, but I haven't heard anything about corners and floor.



Brings up another interesting point: the basket has to go around the flue-terminal, and technically speaking (as in "corgi-technical") the flue is the coaxial bit. afaik

Lowering or sloping the outside ground level would be a way.
Maybe a twin flue model.

Not sure I quite follow this.

The PRV will be into a sump pump tank that is already in the basement (see the white pipes in the picture above) or in a holding tank under the basement (less likely as it would not pump).

There would also be a condensate pump put into the drain you can see above too.

Charles.

 

[MrFrisbee]

....and the flue cannot be turned outside (as it is an internal flue only).

That is somewhat unlikely

So, we either have to box the flue in outside and raise it (so it is not technially "outside)

That is not an option

or I can have the ground below the flue lowered (as it has been excavated anyway for some drain changes. We can infill the hole but leave a trough around the flue exit point so that it is 30cm above the lower ground level.

Do you think this is an acceptable solution?

Not really. If the flue is in a trough, the fumes will mix with the air used for combustion in an unpredictable way.

Which boiler is going in?

The idea of boxing in outside was actually the manufacturers.

Boiler is an Alpha CD50.

 

[bengasman]

2 options.
You misunderstood something.
I am getting something wrong.

I have a feeling that at least on the "internal flue only" it is you.

 

[bengasman]

The idea of boxing in outside was actually the manufacturers.

Boiler is an Alpha CD50.

Where you present when the installer called the manufacturer?

 

[DazzarGaz]

Thats a very bad location!

As you know the regs state that the terminal has to be 300mm above the ground. That's for the outlet for the flues gas AND the air inlit.

If it's below 300mm the unsafe situation say NCS. However they also say if there is a risk of PoC re-entering the property then it's AR. Looking at the picture, I'd be doing a lot of FGA checks and I'd be leaning towards AR.

Using a plume management kit normally does not allow you to circumvent the requirements for the location of the terminal as you can't move the air inlet. The dangers arising from a partially blocked air inlit are just as real i.e. excess CO been producded due to incomplete combustion.

However Worcester have changed their guidelines in the last few weeks so you can deliberately use a plume management kit to get out of awkward situations. You have to ensure then that the air inlet is kept clear of stuff like leaves during the autumn and snow during the winter etc.

Is there no way of getting an extra 10cms?. How about having a 45 degree elbow on the other side of the wall and going through the wall at an angle?

And don't forget your flue guard!!!.

 

[MrFrisbee]

The idea of boxing in outside was actually the manufacturers.

Boiler is an Alpha CD50.

Where you present when the installer called the manufacturer?

I called the manufacturer and they said the flue cannot be "turned" outside. They then called me back with their suggested solution of boxing it in outside.