Jump to content

Woodburning flue clarification


Featured Posts

4 minutes ago, lewisericeric said:

Hi guys

 

I can't make out if it's mandatory for BSS or just recommend but do flues now HAVE to be double-skinned? 

 

Are single skin flues still allowed in new builds? Always thought they were better re extra heat from the flue itself 

 

 

They ARE better, loads better. 

 

It's what happens when lawyers start getting involved in building work. 

 

Where in the BSS do you think it says twin wall flues are mandatory?

 

 

  • Greenie 2
Link to comment
Share on other sites

12 hours ago, lewisericeric said:

Hi guys

 

I can't make out if it's mandatory for BSS or just recommend but do flues now HAVE to be double-skinned? 

 

Are single skin flues still allowed in new builds? Always thought they were better re extra heat from the flue itself 

 

It's not mandatory, just recommended.

 

Just pay attention to any manufacturer recommended distances to combustible materials, as any sign of heat damage or scorching to to these areas would be a BSS fail. 

Link to comment
Share on other sites

14 hours ago, MtB said:

 

 

They ARE better, loads better. 

 

It's what happens when lawyers start getting involved in building work. 

 

Where in the BSS do you think it says twin wall flues are mandatory?

 

 

The BSS site has a link to an installation diagram and it states on there about a double-lined flue. It's not exactly clear if this is mandatory or not, which is why I was checking on here. My boat is a new shell, so I can't get away with it being deemed as acceptable cos it's an older boat... just wanted to check.

 

I've heard other stuff about twin wall flues being better for draught/draw though? and less smoke when opening the door of the stove to refuel?

Link to comment
Share on other sites

Twin wall flues keep the flue gas warmer  so it rises faster and produces a better draw.  That causes the fire to burn faster, unless you reduce the primary air supply (bottom control, usually). However, reducing the heat loss from the flue is the same as reducing the heat gain to the boat. In theory the reduced heat gain from the flue is balanced by the heat from the brighter fire which is at lower level so more useful.  You burn more fuel for a given heat output to room  and more heat is transferred to the air from the flue gases after they leave the chimney.

 

Reducing the primary air supply initially lowers the pressure in the fire box,  so less initial smoke when you open the door,  until the fire slows when it all goes back to equilibrium, but the better draw for the same heat input will still help keep the smoke in the heater, not in the room.

 

The CoP seems to  assume that more draw= brighter fire=more heat=less CO is what is needed for a boat installation.  Hmmm.

 

N

 

Link to comment
Share on other sites

1 minute ago, BEngo said:

In theory the reduced heat gain from the flue is balanced by the heat from the brighter fire which is at lower level so more useful. 

Since the only way heat gets from the stove into the surrounding space is by radiation and convection from hot surfaces, reducing the area of hot surface by insulating the flue means that in order to maintain the same output to the room the stove body would have to be considerably hotter or considerably larger. A hotter stove would mean an increased risk of radiant heat damage to nearby surfaces and reduced life of stove components. A larger stove would be safer (but more expensive and space-consuming), and the larger grate would probably mean a bigger fire, offsetting any fuel savings from more efficient combustion.

Keeping the flue gasses hot may possibly result in an increase in combustion efficiency (heat out per unit of fuel burned), but insulating the flue will reduce the effectiveness in terms of heating the space.

It's a complete nonsense!

  • Greenie 3
Link to comment
Share on other sites

I suspect the 'elfin safety police like the twinwalled  flue and are desparately trying to find reasons to justify it.

I also supect the rules/recomendations are based on domestic (house) concepts and carried over to boats.  In a house a lot of the flue is often up inside the chimney breast so does not radiate heat into the living space, so a twin walled flue makes sense. However, a boat is not a house.

Link to comment
Share on other sites

Single skinned, every time. Easier to fit, look immensely better and as others have said help warm the room. I think the elf and safety aspect is to stop numpties swinging off the flue on entering a boat with stove near door and getting burnt. Stupid people will do stupid things whatever safety precautions are put in place.

  • Greenie 1
Link to comment
Share on other sites

54 minutes ago, mrsmelly said:

I think the elf and safety aspect is to stop numpties swinging off the flue on entering a boat with stove near door and getting burnt.

In which case the sensible precaution is to put bars or perforated screens around the flue, to prevent direct contact, but allow radiation and air circulation.

Link to comment
Share on other sites

4 hours ago, lewisericeric said:

The BSS site has a link to an installation diagram and it states on there about a double-lined flue. It's not exactly clear if this is mandatory or not, which is why I was checking on here. My boat is a new shell, so I can't get away with it being deemed as acceptable cos it's an older boat... just wanted to check.

 

I've heard other stuff about twin wall flues being better for draught/draw though? and less smoke when opening the door of the stove to refuel?

If its new I don't know how the RCD effects things. (I know its not the RCD now but can't remember the new names)

2 hours ago, mrsmelly said:

Single skinned, every time. Easier to fit, look immensely better and as others have said help warm the room. I think the elf and safety aspect is to stop numpties swinging off the flue on entering a boat with stove near door and getting burnt. Stupid people will do stupid things whatever safety precautions are put in place.

But they can and probably do put there mitt on the hot stove top now and again.

Link to comment
Share on other sites

5 hours ago, BEngo said:

Twin wall flues keep the flue gas warmer  so it rises faster and produces a better draw.

 

 

Yes true, but with all the stoves in all the boats I've ever owned the main problem had been slowing down the gas flow up the flue and reducing the draw. The last thing it needs is making it flow faster! 

 

Also, by having hotter flue gas one is losing and wasting more heat energy up the flue. 

 

 

  • Greenie 2
Link to comment
Share on other sites

On 19/08/2022 at 19:16, MtB said:

Yes true, but with all the stoves in all the boats I've ever owned the main problem had been slowing down the gas flow up the flue and reducing the draw. The last thing it needs is making it flow faster! 

 

I agree.  It is of course easy enough, (with a good, controllable stove) to slow the flue gas, but then either  the blasted fire goes out or the wind gets up and a gentle warmth becomes something suitable for climbing Shap!!

 

N

Link to comment
Share on other sites

  • 3 weeks later...
On 19/08/2022 at 03:26, MtB said:

 

 

They ARE better, loads better. 

 

It's what happens when lawyers start getting involved in building work. 

 

Where in the BSS do you think it says twin wall flues are mandatory?

 

 

I was told when our stove was replaced  to take out and refit same stove old flue is good to go however replace with a new replacement stove has to conform to new standard ie double skin flue

Link to comment
Share on other sites

2 hours ago, Oddjob said:

I was told when our stove was replaced  to take out and refit same stove old flue is good to go however replace with a new replacement stove has to conform to new standard ie double skin flue

 

At home or on a boat? On a boat I think that you have been told a load of bull. Yes, there is a BS on stove installations or boats, but it is NOT mandatory, it is a recommendation and arguably best practice.  The argument bit is about insulated flues. I don't know how the RCD/RCR affects this but in general that is more applicable to a new build rater than replacement or repairs as far as the majority of inland boaters are concerned.

Link to comment
Share on other sites

I've had two narrow boats in my life. the first one had a single skin flue and, as said the heat from the flue does augment the fire heat. I did clad the bottom with a perforated plate because I had children on board and my fire was next to the door steps so for an unthinking person and kids tend to be of that ilk, it would have been reasonably easy to put a hand on the flue. I also put a grid made from an old oven shelf on top of my stove. My second boat had a twin walled flue for the same reason as before but I installed that. It was significantly cooler on board. I think the diagram that lewisericeric is referring to is for houses that do have mandatory regulations in place. Boats are advisory at the moment BUT it is a good idea to follow MOST of the advice in that diagram especially the distances from combustable objects. I used that diagram when I installed my stove on my boat.

Link to comment
Share on other sites

5 minutes ago, pete.i said:

BUT it is a good idea to follow MOST of the advice in that diagram especially the distances from combustable objects. I used that diagram when I installed my stove on my boat.

 

I used the house regs for distances and hearth size/depth when I installed mine, the boat BS had not been thought of then. When the boat BS came out the stove complied apart from the flue. I would favour a punched flue guard if it was likely that anyone would touch the hot flue rather than an insulated flue. I would insulate the gap between the inner and outer of the chimney, but that is to do with minimising tar runs rather than safety.

Link to comment
Share on other sites

43 minutes ago, Tony Brooks said:

I don't know how the RCD/RCR affects this...................

 

 

I have never been able to identify any RCD / RCR requirements relating to solid fuel stoves (I guess they never considered that a SF stove would be used on a boat)

 

(Maybe it is there but tucked away in some obscure 'corner')

 

The only 'heating' related section relates to gas :

 

5.5 Gas system

Gas systems for domestic use shall be of the vapour-withdrawal type and shall be designed and installed so as to avoid leaks and the risk of explosion and be capable of being tested for leaks.

Materials and components shall be suitable for the specific gas used to withstand the stresses and exposures found in the marine environment. Each gas appliance intended by the manufacturer for the application for which it is used shall be so installed in accordance with the manufacturer’s instructions.

Each gas-consuming appliance must be supplied by a separate branch of the distribution system, and each appliance must be controlled by a separate closing device.

Adequate ventilation must be provided to prevent hazards from leaks and products of combustion. 

 

All watercraft with a permanently installed gas system shall be fitted with an enclosure to contain all gas cylinders. The enclosure shall be separated from the living quarters, accessible only from the outside and ventilated to the outside so that any escaping gas drains overboard. In particular, any permanently installed gas system shall be tested after installation.

Link to comment
Share on other sites

Use a single wall flue for efficiency but surround it with a perforated stainless steel guard for safety so that it is now twin wall. There is nothing that says the extra wall must not be perforated!

 

There is no requirement for twin wall in the regs for building a new boat.

Link to comment
Share on other sites

  • 7 months later...
9 minutes ago, casper ghost said:

I have a question about twin wall, if you already have the cast iron, through roof flange, can a twin wall be retro-fitted? What goes through the roof part? obviously a twin wall wont fit. Thanks

Depends how big a hole you want in your roof!

Twin wall is a waste on a boat IMHO.

Link to comment
Share on other sites

Just now, Tracy D'arth said:

Depends how big a hole you want in your roof!

Twin wall is a waste on a boat IMHO.

It isn't for me, but someone I know wants to do it, ideally they'd like to keep the cast iron flange, wondered what other people had done? I'm sticking to single skin, worked fine on our boats for 40 years..

Link to comment
Share on other sites

3 minutes ago, Tracy D'arth said:

Twin wall is a waste on a boat IMHO.

 

 

I measured the surface area (radiant area) of both the stove and the flue, they were almost identical.

 

It seems pretty ridiculous, to me, to be sending almost half of your produced heat up the flue and out of the chimney, when it could be radiant heat inside the boat.

Having a twin wall flue means you need to burn a lot more fuel to get the same heating inside the boat.

Edited by Alan de Enfield
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.