URGENT - Do I need a register plate or not?

[Tom]

I'm having my multi-fuel burner installed in a couple of weeks, using flexi-flue. The chimney is quite large and tall. I don't want to have a register plate at all ; to allow heat up the chimney, to keep the void warm and stop condensation on the wall and to keep the gases warm in the flue. I don't want to fill the void with vermiculite. The HETAS installer says he understands this but Building Regs say he should install a register plate to stop hot debris from falling onto a combustable material. We have stone walls and floors but he says someone might put a rug down, for example. He says, to cover himself, he can put a couple of vents in the plate to allow heat up but catch any falling debris. Before I pay for the expense of the plate, can anyone tell me;

1. Do I really need a plate?
2. If so, why? Is it for the reasons he gave?

I need to know pretty quick if I'm not going to have one, so I can stop him from making one. Thanks.

Jaqy

 

[shelli]

I have um-ed and ah-ed about this for you for a few minutes - What I keep coming back to is that if you don't have a plate wont you lose a significant amount of heat up the chimney? - and, if you are losing a lot of heat to the chimney, what is point of having flexi liner and wood burner?- you might just as well have an open fire.

But condensation etc big problem - so why not let the guy do you a plate with extra vents in - air can still circulate - ambient temperature in chimney and nice warm room

 

[Pford75]

With respect, none of us on the forum are HETAS engineers (unless they've been keeping it quiet)

This is one area (like gas fitting) where I leave it to the experts.....I don't know why you would go to the hassle of using a HETAS engineer and then ignoring his advice.

 

[Tom]

I'm not ignoring his advice, simply questioning it. As we already know, many tradespeople are used to dealing with modern buildings and it's perfectly feasable that he wants to install a plate because that's what he always does. That doesn't mean he's right! Neither does it mean that Building Regs demand one. If I'd listened to a lot of the 'advice' I've been given over the years, my house would be a real mess by now.

Jaqy

 

[Tom]

Shelli, my thoughts about losing heat up the chimney are that it can only go so far and then stop, so I'd only lose a chimney full's worth at the most. Also, we have underfloor heating, too, so the wood burner is more for 'show' than anything else.

Like you say, condensation is the real problem and it's taken months to dry the house out. The last thing I want is a chimney-shaped dark patch of wall, full of condensation!!

I might give Building Control a call on Monday and see what they say. If I get everyone's opinion, I can make an informed decision. Thanks, Shelli.

Jaqy

 

[Flyfisher]

I'd want to know where the 'hot debris' that might fall on combustible materials is going to come from? If your liner goes all the way up to the top of the pot, how can anything fall back down the chimney?

Having said that, for better or worse, there is a certification issue here, as Pford75 points out.

I think register plates are allowed to have access/inspection flaps in them; how about just leaving them open if you want to warm the chimney?

 

[middi]

Jaqy, I have fitted about half dozen woodburners in existing chimneys and inglenooks and all I did was to feed the correct size double stailess steel liner down the chimney and connected it to the burner outlet, sealed the s/steel cap on the existing chimney pot and they all worked extremely well. If the stack is mainly external it does help a bit if you insulate the liner but the amount of heat you loose is not much to worry about, don't get bogged down with too much red tape, if you are unhappy with just a liner with no insulation and register plate you can alays retro-fit.

What you have done is a big step up from an open fire and there is nothing illegal about those.

 

[Tom]

Thanks, Middi, you're on my wave length exactly! I'm definitely going to call the BCO on Monday and get his take on it, too. Thanks again.

Jaqy

 

[Penners]

Jaqy - I would always go with a register plate and a chimney-full of vermiculite. This will keep your flue liner good and hot right up to the top, largely preventing the condensation of acidic combustion products inside the liner.

These acids can sometimes eat through a liner remarkably quickly. It's impossible to be specific about the problem, because every installation is different, but I once lost a "naked" liner in only three years.

(Gosh - I've never disagreed with middi before. I'm very nervous. )

 

[Tom]

Hi Penners, I trying sooooo hard to get my head around this!! Are you saying that if I don't have vermiculite or a register plate, the flue will not be warm enough to get rid of the gases, even though room temperature air will be filling the chimney up? I'm confused :?

Jaqy

 

[Penners]

I'm saying that's a possibility, Jaqy. Your room certainly won't be as warm as the heat going up the flue from your fire, so that temperature differential could cause condensation within the flue.

But of course your BCO and your installer will be much more knowledgeable on this than I am.

 

[Andrew Bodenham]

The register plate has several functions. Firstly it provides lateral restraint to the flexi flue liner at the point where it joins your stove pipe. Secondly it retains any insulant backfill in the chimney. Thirdly it prevents dust, soot etc. falling out of the old flue.

Part J of the building regs is a bit wooly on detail - you can read it yourself online on the website of the Deputy Prime Minister and download for free.

In my opinion you should be insulating around the new flue liner, either with an insulating jacket or with an insulant backfill. This is important in order to keep the whole liner at a high temperature so that steam, tars etc. do not condense out in the upper reaches of the liner. As Penners has said, the condensate is acidic and can corrode the liner; tar deposits can build up and lead to obstruction of the liner or a fire in the liner. An uninsulated liner can have real problems when the stove has just been lit from cold, as large quantities of condensate can cascade down liner and leak out from joints, access caps etc. I have seen this happen.

I would not be concerned about the possibility of condensation in the space between the liner and the walls of the flue. Once the stove is running steadily the whole flue will gradually warm up, and this will drive out any residual moisture. In fact, I would consider condensation more likely if the bottom of the flue was left open (i.e. no register plate) as this would allow relatively warm, moist air from the room to enter the flue. This air could then rise up in the flue and could possibly condense on the cold masonry higher up (when the stove was not in operation and the flue was cold)

To summarise: fit a register plate, insulate the flue, go with your installer's advice.

 

[middi]

Jaqy, Penners and Andrew have ,without doubt, explained that by fitting a register plate and backfill with vermiculate will (should) keep the acidic condensation to an absolute minimum and therefore safeguard the longevity of the S/steel liner. You cannot go wrong if you follow this approach. Also due to the thermal efficiency of the insulated liner this will reach an operating temperature quite quickly hence heat recovered to warm the room as opposed to warming up the liner and brick/stonework.
There are lots of variables to consider in order to decide if the basic " just push flue liner down the stack" approach will work . If ( for example) the chimney stack in mainly internal, such as centrally situated within the building, and the woodburning stove is kept going more or less permanently during the winter months it actually may be more efficient to just fit a liner and allow the brick/stone stack void to warm up as this will act as heat reservoir to irradiate back into the house.

If, on the other hand, the chimney stack is weather exposed and you are likely to fire up the stove from cold very frequently, then a well insulated approach is required. Other scenario's somewhere in between as described above will work pro-rata for or against.

If you cannot decide which end of the spectrum your stove falls then INSULATE. There are no fast rules to follow, exept well advised guidelines( particularly true for existing stacks).

 

[Tom]

Thank you to everyone who has given me good advice and explained the pros and cons of each approach. It's certainly helping me to decide on the right way to go!

So, taking everything into account, I want to insulate the flue with a 'jacket'. How is this done? Before it goes in the chimney or once it's in place? Is there a special procuct to use? Does it have to go all the way up the flue from the point where it joins the stove pipe, or just at the top? If just at the top, how much down from the top?

Thank you to anyone who can answer these questions.

Jaqy

 

[Penners]

The usual method is to use a double-skin, factory-insulated flue liner. Here's an example (picked at random - not because I have any personal experience of it): http://www.stovesonline.co.uk/wood_burning_stoves/Selkirk-flue.html

However, speaking for myself, even if I used a liner like this, I would still fit a register plate and backfill the chimney with vermiculite. It's a belt-and-braces approach, but I'm convinced that it would still repay the relatively modest extra cost. Insulated flue liners are not cheap, so anything you can do to maximise their lifespan (within reasonable cost limits) is likely to be worthwhile.

 

[Tom]

Hi Penners

I'm definitely using a double skin flue but definitely not backfilling with vermiculite. I need something now to wrap the flue in.

Jaqy

 

[Penners]

OK Jaqy - I reckon your installer will have much more information and suggestions than me.

Unless you've got a drawer full of old rugby socks?

 

[FamilyWiggs]

OK Jaqy - I reckon your installer will have much more information and suggestions than me.

Unless you've got a drawer full of old rugby socks?

Do you mean "many more" suggestions?

P.Edant. :lol:

 

[Penners]

Touché!



(Smart@rse)

 

[Nemesis]

I suppose stretching things that (if spoken) could be deemed elision... or more properly, as it is written, ellipsis...

However:

I reckon your installer will have much more information and suggestions than me

Possibly, alternatively, than I (have)?

Just raising the issue in the cause of advancing pedantry, natch...


(No there is no right answer really.)