An old CLV (3CE, LAS) is renovated inside the existing pipes: the old inner pipe stays in place as a casing and the outer jacket remains the air supply. Inside goes one new common flue (C14/C13) or a separate flexible liner per boiler (C15).
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An old CLV consists of two concentric stainless steel pipes in a masonry casing. Flue gas went up in the centre, air came down in the jacket around it. On top sits one cap: air enters through a mesh basket, flue gas leaves through the middle.
What happens in a CLV renovation
The old inner pipe is not removed. It becomes the casing for the new liner and carries no flue gas any more. The jacket keeps its job: supplying air, in counterflow, through the existing mesh cap. Each boiler gets a concentric connection through the shaft wall. The outer pipe of that connection ends open in the jacket and draws air there. Only the flue pipe continues through the wall of the old inner pipe.
Around that passage goes an ALU sealing collar per connection (80/125 or 60/100). It closes the opening between the jacket and the old inner pipe, so the air does not leak into the casing of the liner.
Which system fits your CLV
| Old inner pipe | C14/C13 | C15 with ø80 liner |
|---|---|---|
| ø250 (jacket ø400) | One column, diameter from the calculation | Up to 4 liners |
| ø300 (jacket ø450) | One column, diameter from the calculation | 5 liners comfortably, 6 tight |
| Not straight or not round | PR C14 Flexible | C15, the liner follows the pipe |
Inner pipe and jacket come in fixed pairs: measure the inner pipe and you know the jacket. In an old CLV the room inside the inner pipe sets how many liners fit; the jacket has enough air.
How to build your list
- Measure the old inner pipe and the height of the CLV to above the roof.
- Check that the pipe is straight and round over the full height.
- Count the boilers and note their connection (80/125 or 60/100). Count one sealing collar per boiler.
- Choose C14/C13 or C15 and enter the number of boilers and the height in the list builder.
- Send the boiler data with your quote request and we check the diameter to EN 13384-2.
Frequently asked questions
Does the old inner pipe have to come out?
No. It stays in place as a casing around the new flue. If it is no longer straight, choose a flexible liner.
Where does the air come in after the renovation?
Through the existing CLV mesh cap, as before. The air flows down the jacket to the open outer pipe of each boiler connection.
Why a sealing collar per connection?
The jacket has to stay airtight towards the old inner pipe. The collar closes the opening around the flue pipe.
Does a CLV have to be inspected?
Yes. In Flanders the inspection of the chimney or flue is part of the mandatory maintenance of a gas boiler, every 2 years.
