Flue dodging

16 Jul 2008
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Hi there,

Got my Vaillant boiler pack from Mr Central heating today. They left the standard horizontal flue kit in the pack even though I ordered a vertical flue kit to pop out of the flat roof above the boiler.

Anyway - I realised today that unfortunately, where my vertical flue wants to go straight up and out of the flat roof, it will interfere with the eave of a section of pitched roof that overhangs onto this flat roof by about 3". Bugger!

I could hack the eave about a bit but that could be a bit messy in terms of waterproofing. I could also space the boiler about 3" off the wall i'm putting it on and the flue would go up and out without fouling the eave, but that seems a bit of a bodge too as it will make the pipework under the boiler a bit messy as it all doglegs back to the wall.

Since i've got the un-needed horizontal flue kit, I've already got a 90 degree elbow. If I get another one I could put the two together to create a 'dogleg' then put the vertical flue on that. That would mean the boiler can go where it wants to, and the vertical flue will miss the eave.

Question is, is that OK? I've seen using a pair of 45s with some straight between to achieve a similar goal externally, but since I've already got one 90 I thought I could use that and get another. Also I'm not sure i'f i've got the space between the boiler and the roof for a pair of 45s with some straight between.

Last question - my boiler is a vaillant ecotec pro but the vertical flue kit they have supplied appears to be glow-worm. It's identical to the vaillant bits though and goes together fine. I assume it's OK to mix manufacturers flue bits if they are compatible?

All help appreciated. Cheers,

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Nothing up with using 2 elbows how you want by the way they are 87 degrees, each elbow equals 1 metre of flue (with the first elbow straight off the top of boiler usually ignored)
So even if elbow was counted you hav 2 elbows = 2metres and vertical flue kit 1 metre in length so it meets maximum permissable flue length.
But will it meet clearance distances outside structures , they are in the book

You will need a bracket to support the elbows to the ceiling.
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Ah thanks - a useful reply without a sarcy comment! :)

Don't worry - I wouldn't presume to think I'm competent enough to carry out such tasks myself (I'm a lowly mechanical engineer) - my friend is a real Corgi and will be doing all the bits he's supposed to do. Yes I know that includes fitting the flue and even the boiler wall bracket (though I might tackle the latter myself and just make doubly sure he checks my work. Probably do a pull-out load test on the fastenings to be safe).

Just thought I'd ping the question here so that i might have the solution/parts etc ready (Corgi is on holiday you see). The Vaillant flue manual uses two elbows in a similar way to avoid a horizontal obstruction - i.e. boiler elbow sideways connected to another elbow facing rearwards, connected to standard horizontal flue piece. I want to do a similar thing vertically - i.e. boiler elbow facing forwards, connected to another elbow facing upwards, connected to my vertical flue termination.

Regarding 87/90 degrees - I know you'd use 87 elbows for long extensions runs as you need to keep the horizontal extensions rising. However the elbow supplied in a standard horizontal flue kit appears to be a 90. This allows the horizontal pipe to exit straight out of the wall. The rise is provided by virtue of the fact the inner plastic flue pipe is pulled to the very top of the air pipe by the time it reaches the grill.

So i'm pretty sure i've got a 90 so will need another 90 to complete my dogleg. As opposed to using a pair of 87s, this technically creates a very short length of purely horizontal flue, but no more than on a standard horizontal flue kit. So hopefully should be OK?



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