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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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General: Log burning fridge

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    • CommentAuthorMarkBennett
    • CommentTimeJan 30th 2012 edited
     
    Posted By: JontiIs there a reason why the inlet pipe for air couldn't be run down the chimmney?

    My fire place is in the middle of the house with no external walls and a solid floor so I do not know how I would get an external airflow if I did need one.

    Jonti


    One of the concrete block chimney systems can do this. There is a separate "duct" running down alongside the flue to supply combustion air to the stove. It looks an elegant solution but it was unclear if it had approval in the UK market. It was mainly being pushed for Southern Ireland. If you're interested I can try to dig out the details.
    • CommentAuthorJonti
    • CommentTimeJan 30th 2012
     
    Posted By: MarkBennett
    Posted By: JontiIs there a reason why the inlet pipe for air couldn't be run down the chimmney?

    My fire place is in the middle of the house with no external walls and a solid floor so I do not know how I would get an external airflow if I did need one.

    Jonti


    One of the concrete block chimney systems can do this. There is a separate "duct" running down alongside the flue to supply combustion air to the stove. It looks an elegant solution but it was unclear if it had approval in the UK market. It was mainly being pushed for Southern Ireland. If you're interested I can try to dig out the details.


    If its no trouble it would be interesting to see.

    Thanks Mark
  3.  
    • CommentAuthorowlman
    • CommentTimeJan 31st 2012
     
    A neat solution Mark, and one that would be easy to replicate in a more traditional flue build. I think though their air intake is a bit suspect being close to the smoke outflow. I would have been tempted to put the air intake lower, on the side of the stack with a stainless cowl or something, to avoid drawing smoke down the air pipe, especially if the stove has a fan.
    • CommentAuthorBeau
    • CommentTimeJan 31st 2012
     
    When we bought our flue I was told that the difference in atmospheric pressure between the air inlet at the bottom and the top of the flue was what helped create the upwards draw.
    •  
      CommentAuthorJSHarris
    • CommentTimeJan 31st 2012
     
    <blockquote><cite>Posted By: Beau</cite>When we bought our flue I was told that the difference in atmospheric pressure between the air inlet at the bottom and the top of the flue was what helped create the upwards draw.</blockquote>

    Unfortunately this isn't the case, as the static air pressure at the top of the flue is the same as the static air pressure at any close local point that's the same height above sea level and the same goes for the static pressure at the base of the flue.

    Flow up a flue is driven by buoyancy, specifically warmer air (either from inside the house or from the stove when it's lit) is less dense than the surrounding colder air so is more buoyant and so rises up the flue, pulling more air in from the bottom. The effect is just like that used to lift a hot air balloon.
  7.  
    Presumably, the balanced flue chimney systems must include a degree of insulation between the two pipes to prevent the air supply pipe turning into a second flue & thereby defeating the object?

    David
    • CommentAuthorBeau
    • CommentTimeJan 31st 2012
     
    Unfortunately this isn't the case, as the static air pressure at the top of the flue is the same as the static air pressure at any close local point that's the same height above sea level and the same goes for the static pressure at the base of the flue.

    Flow up a flue is driven by buoyancy, specifically warmer air (either from inside the house or from the stove when it's lit) is less dense than the surrounding colder air so is more buoyant and so rises up the flue, pulling more air in from the bottom. The effect is just like that used to lift a hot air ballo

    Thanks JSH
    I was surprised when I was told it was driven by atmospheric pressure but I did not know otherwise.
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 31st 2012
     
    There is an old joke about an Oxbridge entrance exam where candidates were asked to measure the height of a very tall building with the aid of a barometer, the expected answer being to take readings at top and bottom and from that calculate how much more of the atmosphere the top one is than the bottom, etc, but the inventive candidate suggested many other things instead, such as:

    * dropping the barometer off the top, timing the fall, and using s = 0.5 g t^2 to get the height
    * measuring the length of the shadows of the building and the vertical barometer at (say) noon and working out relative size and thus that of the building having measured the barometer

    etc, etc,

    The punchline is that the candidate's favoured solution is to go to the janitor and say "If I give you this shiny new barometer, can you you please tell me how tall the building is?"

    I now return you to your regular programming.

    Rgds

    Damon
    • CommentAuthorowlman
    • CommentTimeJan 31st 2012
     
    You could say that's like Art and Science, Damon.
    •  
      CommentAuthorDamonHD
    • CommentTimeJan 31st 2012
     
    All science, just rather empirical, and likely to give a more accurate answer than the theoretical version!

    Rgds

    Damon
    • CommentAuthorTimSmall
    • CommentTimeJan 31st 2012
     
    Posted By: Peter_in_Hungary
    I would favour a direct air feed pipe but finding a reasonably priced small stove (below 8kw) with direct air feed is difficult


    Burley do a 4kw stove with a 5" flue, and a direct air feed. I believe it also has the highest combustion efficiency rating of any stove ever tested by DEFRA (89.8%). I was planning on fitting one until I eventually scrapped having a stove due to lack of space to conveniently run a flue...

    When I was going to fit one, I was thinking of sticking it on top of foam glass blocks, and behind a closable pair of doors to stop it doing the aforementioned fridge impersonation when unlit. I was also planning to insulate around the flue, but allow space to selectively draw air around a couple of 2m lengths of single-skin flue pipe in order to extract heat from the flue and move it to other rooms.

    Tim.
    • CommentAuthorJonti
    • CommentTimeJan 31st 2012
     
    Thanks Mark,

    interesting reading,

    Jonti
    • CommentAuthorjwd
    • CommentTimeFeb 2nd 2012
     
    We have an air inlet built into our solid floor (drainage pipe from old sub floor vent grill). It comes up through the hearth. I havent put the stove in yet but I currently have a bit of slate sitting on it and it seems to stop most of the draught. We will see how it works once the stove is fired up.

    Jw

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