Woodburner - water coming in

[88v8]

Rain had been falling for 200 years or so into our inglenook, but I naively assumed that once we had a woodburner+flue liner+rainhat, that would cease.
However, with the recent deluge, water was dripping down the back of the register plate.
And we have't even lit up yet.

Peering through the soot door, I saw that the water was running down the outside of the wrap around the liner. None is falling into the stove, so at least it's not coming down the inside of the liner, thank goodness.

Here is the stack where it was installed. A pot now sits on top of the stack.

Before the pot was fitted, the liner was terminated a foot or so above the closure plate.

The plate was supposed to be sealed with lime mortar before the pot was put on, but to make it absolutely watertight would be very difficult, and I had assumed that a little would leak in and be absorbed by the parging, but not the quantity that came down.

Initially, our HETAS engineer - who I think is not entirely comfortable with thatch - had wished to leave the pot entirely uncovered so that embers could most easily escape, but after I had forcefully pointed out that this would be tantamount to fitting a 6" rainwater pipe into the stove, he conceded that perhaps some sort of rain cover would be in order, so on top of the pot is a coolie hat-type of rainhat, which sits about 4" above the lip of the pot and is about 2" greater diameter. The chimney has a top diameter of 12", and it's hard to find a rainhat greater than 14" dia; I suppose I could make one. However, the greater the diameter, the more chance of embers being deflected down onto the roof, although with a DEFRA-approved stove I think this is not really an issue.

Anyway, I presume that rain has been ducking under the edge of the hat, landing in the bottom of the pot and then finding its way down the flue.

Our existing woodburner also has leaks. In this case the rain comes in through a hole which is there by design in the top of the flue cowl,

but fortunately the water escapes from the liner before reaching the stove, and finds its way out of the back of the register plate. Again, none actually falls into the stove.
I guess it's been leaking like this for the last 20 years.
When my new, longer, ladder arrives, I plan to fix this by attaching a rainhat as an additional layer over the top of the existing cowl.

Is all this sort of thing normal, or have I employed an idiot to instal my new stove? Must I resign myself to a degree of leakage?

A T-pot would be a sure-fire fix, but I wish have to speak with HETAS about its use with thatch, and tbh I don't think a T-pot would look that great on the stack anyway.

Any thoughts welcome.

Ivor

 

[Lime]

In reality you don't know where the rain is getting in.
With the heavy rain we have been having it may be entering through the stack somewhere.
However the space above the closure plate at the top of the chimney appears to be cavernous.
I wouldn't have completely filled it with mortar for several practical reasons.
(although plenty of builders would have done just that!)
So how was it finished off?

 

[88v8]

A layer of mortar on the plate to seal it - don't know how much as I didn't do it myself - then the pot was put in so it sits somewhat within the top coping rather than entirely on it, and flaunched around.
It is entirely possible that the mortar shrank a little even though it wasn't a hot day - there was quite a lot of it and the ladder was struck down immediately the job had been done, rather than being left a day for wetting and patting as it would have been had it been my own ladder.

Yes, tracing the exact source of a leak can be difficult, to say the least. My new ladder has just arrived, so weather permitting I may go up there tomorrow and have a look. Assuming the ladder is long enough, there was a bit of guess work involved when I bought it. :?

Ivor

 

[MdB]

It looks to me as you have a nice hopper on the top of the chimney to collect and funnel lots of water down the flue. Or have a got something wrong here? If it was mine, I would be looking to have a closure plate right across the top of the stone work with the chimney sitting on that. On our chimney, we used a paving slab with a hole carefully cut in the middle. I would fit a hanging flue cowl to the liner such that the majority of the rain is directed over the edge of your pot.

The chimney pot I would flaunch to the paving slab with the dreaded cement with water proofer added. It is an application that wants to be strong and waterproof. This will get the rain onto the outside of your stack.

Ours ended up looking like this:

 

[Lime]

I'd use a square lead collar around the liner/pot as flashing.

 

[88v8]

Thankyou.
A nice hopper... yes indeedy. When there was a fire basket in the inglenook, so much water came down that the thick fire bars were rusted through.
Now, the 'hopper' is supposedly filled up with the base of the pot and the flaunching mortar, so in theory there should be no way for water to get down. In theory...
Except that any rain which ducks under the hat will end up in the base of the pot, which in effect acts like a bucket... a leaky bucket...

So there are three possible leak paths;
- Down the flue liner (not happening)
- Between the pot and the coping (should be covered by the flaunching)
- From the base of the pot, thence down around the closure plate, which is what I suspect.

Your slab... so the pot sits on top of the slab... and is prevented from falling over only by the flaunching? I was nervous of that arrangement because it's pretty windy here, I wanted the pot sitting to an extent inside the stack.
Was also doubtful about a hanging cowl because any rain that ducks under the hat will run straight into the stove. Do you not find that is a problem?
And cement flaunching on a stone stack I thought would be a bad idea so we used NHL5/sharp, although oddly enough reading Hugh Lander last night, he seems very relaxed about using cement in various places.

Lead flashing, how would you attach the upstand?

I wonder if the solution will be to take the pot out... again... drill a descending hole through the side of the stack at the base of the mortar above the closure plate, and insert a copper pipe to act as a drain for any water that gets into the base of the pot.

Ivor

 

[88v8]

Up the new ladder to the stack of the existing woodburner. I can see why water is coming down - the flexy liner has pulled out of its top fixing.
Wonder how long it's been like that. Was dripping last winter, so quite a while I guess.
So that's our main woodburner out of action.
Heyho, another job to do.

As regards the new woodburner with which I started this thread, to be continued no doubt.

Ivor

 

[Lime]

Am I to believe that the liner has been left with an square cavity formed by the walls of the stack open to the elements?
:shock:
I would expect the chimney to be finished off at the very top of the stack with flaunching at least, so water is prevented from collecting and falling down the interior of the chimney.

I propose a lead square cap over the flaunching.
The lead square would be larger than the top of the stack and have a hole in the centre.
At this hole would be a circular upstand next to the liner (i.e. a central hole with a vertical collar formed/bossed around the liner) and the outer edges of the square dressed over the edge of the stack.

 

[CliffordPope]

Ours is as follows:

The chimney pot sits on top of a roughly square hole formed from slate slabs built into the top of the stack about 6" from the top. It is cemented in.

The flaunching is a strong cement mortar with fine ballast, with waterproofer added. This rises in a pronounced curve, to encourage water to run off. It was smoothed off carefully at the join with the pot.

The liner (insulated) was pushed up so that it emerged from the top of the pot, a suspended cowl firmly attached, and then lowered back down so that the base of the cowl sits snugly on the the top of the pot, and overhangs it.

The bottom of the liner is held in a sturdy bracket to take the weight off the cowl, just in case.

 

[88v8]

Thankyou.
We had rain again yesterday, but no water came down. Unlike the previous horizontal rain, this was verticalish. I am pretty sure, therefore, that the problem is rain ducking under the rainhat and running into the base of the pot, then leaking down around the closure plate.

Even though the coping recess is filled to the top with lime mortar, and curved off nicely, this does nothing to deal with water that gets into the pot from the top.

Clifford, the type of terminal you describe would be better. The lower skirt seals the top of the pot, and the rainhat hopefully keeps water out of the liner.
This sort of thing, although not exactly.
http://www.ebay.co.uk/itm/170908405263?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

I contacted Brewers, who make a good selection of cowls
http://www.brewercowls.co.uk/index.php?option=com_content&view=article&id=8&Itemid=11
and they are willing to make specials, at what seems a very reasonable cost. Surprising, for such a large company.

My plan now is to find a wider chinaman's hat - I may already have done so - as a stopgap, and then get a custom cowl made when we fit the taller, larger, pot next year.

So much for the new woodburner....

Back at the existing woodburner, I hacked off the flaunching to find that there is no top clamp at all. A crimp fitting was pressed into the flue liner - has pulled out, surprise surprise - and the top spigot projects through the closure plate with nothing to keep it there but the flaunching. The whole 25ft of 6" liner with its heavy rockwool wrap, was supported on the flue pipe from the woodburner.
Gonna be some changes made. :evil:

Ivor