Chimney Capping

[GordyH]

I have 4 redundant chimneys that need capping.

Has anyone used the Plastic (Teracotta coloured) C-Caps or should I go for the real teracotta ;Mushroom' vent caps

Opinions please

Thanks

Gordon

[Me Here]

Vent caps unless you have other ventilation into the rooms

[Andrew Gabriel]

You need vents at top and bottom of flues, to create a through draft. If the flue is on an external wall, you can create the lower vent to the outside, rather than into the room, and this should reduce heat loss from the room, because you can then block off the flue from the room.

What I've done in one case is block off the flue at the top of the fireplace opening with a piece of plasterboard held in place with some bonding coat plaster, and a few layers of loft insulation on top, both as insulation, and to cushion the fall of any bits of mortar lining which fall down inside the flue. Above this I fitted an air brick through the back to the outside, and a vent at the top. Back of the fireplace is then lined with celotex (it's only a half brick wall, and would otherwise be a cold spot), and the fireplace plastered. Makes a nice hole for the HiFi. Also got a light hidden in the recessed top of the firplace, cable dropped down the old flue from the loft, and fitted a socket in the side for HiFi (avoided back, because cold spot might cause condensation in the back of the socket eventually).

Before I did this, the fireplace had been bricked up with a vent brick into the room for at least 20 years. The pot on the chimney was loose, and I had it taken down and capped. Neither I nor the person who did it realised it should have been vented. Over the next 20 years, the flue slowly, unknown to me, filled up with condensation, to the point where there was water permanently dripping down it. This only came to light when I went to strip the wall paper, found the plaster was all detached from the chimney breast and self-supporting with the aide of the wall paper. Pulled the plaster down to find the chimney breast soaking wet - the separation of the plaster from it had kept the plaster dry and hidden what was going on behind. Fitted a vent at the top and left it all for 3 months, and it completely dried out. It's been bone dry for the 5 years since then, with the vents at both bottom and top. The uncapped flues are also bone dry (in spite of the rain that must come down them), so I would say it's much more important to keep a flue fully ventilated than it is to cap it.

[GordyH]

Thanks for all your input

The C-Cap and the Mushroom both fit onto the exsisting pot but allow for ventilation. The four pots are on a stack of 6 so I want to retain the pots for aesthetic reasons and so will use a vent cap on the pot.

I wondered what the plastic C-Caps look like in real life, they look quite neat in the pictures (google C-Cap)

Unfortunatly my flues are all internal so an internal vent it will have to be at the bottom.

[Roger R]

Where was all that moisture coming from ? I take it you capped but retained the vertical stack above the roof line, so perhaps the rain was soaking down through the stack bricks causing the problem. With virtually no air flow from the room into the chimney cavity that doesn't seem a very likely source.

I too am thinking about closing off a chimney, and from what you say it seems important to reduce the stack to below roof level and roof over. If you had done that do you think any damp could have been avoided ?

Roger R

[Andrew Gabriel]

I wanted to do the same, but didn't want anything particularly obvious when viewed from the ground. Initially I bought a couple of heavy teracotta elephant's foot plugs to go in the top, but decided not to use them because they look ugly (and stop all the pots on the houses matching).

Further searching found the C-cap, and Brewers Chimney Cappers (two fixing styles). C-cap was too small for my pots, and is still quite visible. Brewers Chimney Cappers require either a giant jubilee clip around the pot (yuk) or 3 wing-nuts sticking out (yuk). Anyway, decided to get the Brewers one with the jubilee clip and see if I could mod it to do a hidden fixing.

Anyway, that turned out to be very easy...

(Hum, there are two pictures, but both seem to have the same URL?)

Now, what to do with two elephants feet?

[Andrew Gabriel]

Other one:

Now, what to do with two elephants feet?

>

[Dave Liquorice]

there will be enough ventilation. What do the destructions say about the gap between cap and pot if using the giant jubile clip?

All the commercially avialable caps I've seen have a lot more ventilation that what you appear to have there. Not sure I'd trust 3 bits of 2.5 twisted together copper to support a brick for years at a time, possibly in a mildy corrosive atmosphere inside a chimney. Now some galvanised builders band bolted to the cap bands...

I like it though we have 5 or is it 4 capped flues here and the pottery vent caps up there ATM are pig ugly.

[Andrew Gabriel]

There's between 1-2cm all around. It's a bigger gap than it would be with the jubile clip because the straps are folded back on themselves and the cap is sitting on them (and I bent them by hand, so it's not a tight fold back). It's a lot more than the classic air-brick in the side of the stack (which is what I've done for the flue which has been flaunched over). The instructions for jubilee clip fitting say ensure there's a 5mm gap all round.

Somewhat annoyingly, after I'd repaired the flaunching over the missing pot and I was going around the roofing suppilers looking at caps, I found one which had a reclaimed pot to match the missing one. If I'd found this before repairing the flaunching, I would have fitted it to restore the full compliment for the sake of appearances.

I had some non-galvanised steel cable (lashing cable for aerial chimney bracket which I didn't use in the end). I thought the copper would last longer, and I don't expect it to be particularly corrosive in there. Seemed like a good way to use up some red+black T&E too;-)

This capper says it's designed for 5-10" pots. Mine are actually

11-12", so it's more flush fitting with the sides than they intended it to be.

Just wondering if I take the pottery ones back (less 25% resocking fee), or plant them out with something interesting for my nephew. They are quite heavy (much heavier than a normal planter).

[Dave Liquorice]

about

Ah it looks a lot snugger than that in the picture, ample space.

I'd expect the aerial lashing wire to be galvanised but then... Just thinking that copper is quite soft and will stretch and thus weaken over time, particulary at the stress points on the corners of the brick.