I would like to install a coal fire or possibly a gas fire in an open fireplace in my house. This will be in the living room and will provide a major portion of the house's warmth in Winter, as I don't have central heating.
What I am concerned about is finding that too much of the room's warmth escapes up the chimney especially when the fire is not lit. And also the possibility of cold drafts coming down the chimney.
What is the best (and hopefully inexpensive) way to minimise this? Is thare any kind of one-way-flow system for chimneys and/or fire flues?
*A lot* of warm air goes up a chimney. We have a rectangular opening for the grate and I made a board with brush type draft excluder around the edge that fits snugly into the opening. Have a look for chimney balloons.
*A lot* of warm air goes up a chimney. We have a rectangular opening for the grate and I made a board with brush type draft excluder around the edge that fits snugly into the opening. Have a look for chimney balloons.
Chimney balloons are only good for *blocking* the chimney to reduce heat loss due to down draught and some heat loss upward if the hearth is not in use entirely. I get the impression that the OP wants something to prevent downdraught without losing too much heat *UP* the chimney rather than block the entire chimney and releasing noxious smoke and fumes into the room when it gets lit !
A simple flap will solve this when the fire is not lit preventing downdraught.
My thoughts on this matter are that in my place I have a grid in the upstairs section of the adjacent chimney breast that a fan blows warmed air from the heat escaping up the chimney hearth below through a matrix of simple tubes through the upstairs chimney breast providing airflow through the grid to warm the room above and upstairs if the doors are left open to circulate. The non used chimney in the upstairs is blocked at the top at the pot preventing airflow down and up.
We have a chimney balloon (giggle for "chimney balloon", SWMBO tells me) for each fireplace, they are to be recommended particularly if you have a fireplace that's not used too often.
A chimney with anything but occasional (as in a handful of times/year) down draught has something wrong with it.
Damper flap, chimney ballon, ball of newspaper all do the same thing and all need removing (or opening) before the fire is used. Ballons come with a big red tag on a bit of string that dangles into the opening. A forgotten ball of newspaper might make for an interesting few minutes as bits fall down and others are carried up and out of the pot still burning...
What I used was an old foam pillow wrapped in a plastic bag, works great because the foam is so springy and the plastic helps to block air. There was smoke rising up from the fire downstairs and descending down the flue into my room, *cough* worse than 40 cigarettes a day.
Having had an open fire in my previous house, I really most strongly recommend an enclosed stove. They produce a /lot/ more heat when on (*), and there are no drafts up the chimney when off.
This is not a particularly cheap option though. You will need a liner for the chimney - particularly with a coal fire.
(*) I hypothesize this is because a stove can get away with much lower air flow than an open fire without letting smoke in the room. The reduced air flow means the heat of the fire stays in the room, rather than flying up the chimney.
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "AL_n" saying something like:
In a draughty cottage living room I improvised a simple wooden board that went over the firehole when the fire wasn't lit. It made a tremendous difference to the room temp.
There is still quite a draw on a stove but instead of a gert big grate and open flue to the top you have rextrictions and covers you can close. The higher output is more likely down to better combustion of the fuel and the fact that the fire is contained if gert metal box that gets damn hot radiating and convecting heat into the room.
Its a bit better than that, I agree with what you say, but there are some other issues.
In general the efficiency of a thermal device - and this is as true for steam engines as it is for a stove, is that the higher the working temperature is and the lower the exhaust temperature is the more heat you have extracted from what's in the chemical reaction in the first place.
Now if you havent actually burnt all that you could, so tars and CO and so on are going up the flue, that's an area to tackle, and for whatever reason stoves do work better in that respect. I suspect by concentrating airflow into the combustion chamber more effectively than an open fire, especially an open fire 'throttled back'. I.e. you are burning less fuel hotter and more completely.
That is essentially a more detailed description of what you said.
However..
In addition, most stoves do not exhaust to the flue directly. The epitome of that is the Aga, where the actual flue path is past a couple of hot plates and around several ovens before getting to the flue pipe by which time the gas temperature is well below 100C - I can put my hand on ours. And by the time our pipe disappears into the actual flue itself at ceiling height, its around 40C or less.
That means the ratio of what is initially burnt at 650C or so (red hot in the oil vaporizing chamber to what comes out (40C) extremely high. I would say that our aga is infinitely more efficient than the non condensing oil boiler and better than most condensing boilers, in terms of heat retained inside the house to what goes up the flue.
A similar sort of trick happens in the woodburning stove we have. The flue is a lot hotter, but throttled back, its in the 60-70C range. Despite being red hot in the combustion chamber.
This contrasts with the sort of 200C -3O0c flue temps of an open fire.
However in that case, the flue is inside the house and walls get distinctly warm that contain it - its not insulated. So I cant say what the final exit temp as it passes the insulation barrier is.
So I think that aspect of a stve is ayt east as important as the actual efficiency of combustion.
They really are extremely good devices to get rooms warm.
However they don't have the character of a blazing open fire in an inglenook!
So we have those as well!
And they are actually pretty efficient if cranked up to full probably
10Kw style output. Running nearly white hot in the grate and with unisulated flues.
Our stoves have front-opening doors and when we feel like a bit more atmosphere we can throw the doors open and enjoy the noise, flicker, etc. Of course the efficiency and safety aspects might be reduced but that's our choice and it's not for long.
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