restoring a real fire on my house - advise needed!

A._Badger

grahamc2003 wrote: »

I love open fires, the sound and especially the smell. But none of that changes the thermal characteristics of them, and I'm afraid, you can get efficiencies of less than zero (i.e. more useful heat is lost than actually generated) under the worst cases - so worse than the 10% efficiency quoted (i.e. 90% of the heat lost, if that is what the 90% is).

If you have central heating at a high room temperature and low ambient temp, then lighting an open fire can make the room cooler, simply by the fire causing more room heat being dragged up the chimney than the fire is generating (which of course sucks in cold air from the outside).

For more normal and typical circumstances (i.e. an open fire in an otherwise unheated or very lowly heated room), then there'll be a positive efficiency, but I doubt it would be much higher than 10-15% typically. (I'm only the messenger btw, and not saying that therefore open fires are crap). Basically it's a balance between the radiant heat into the room vs the heat exiting the chimney - and the radiant heat can burn your legs and make you hot even at these lowish efficiencies and a low room temperature.

Stoves simply restrict the air up the chimney to the minimum possible to fully burn the fuel and no more (if set correctly). So the gain of a stove over an open fire is twofold - the complete combustion of the fuel (you can't get that with an open fire), and the (massive) reduction of heat loss up the chimney. It doesn't matter how much you like open fires or dislike stoves, or vv, those characteristics still stand.

I've read, and believe, that stoves are typically 7 times more efficient at heating a room than an open fire, and that backs up my experience when I ripped out my open fire and installed a stove. The tradeoff seems to be for an open fire, you need typically seven times more fuel than for a stove, and for some, that cost will be worth paying to keep the ambiance an open fire creates.

With respect, the problem there is 'read and believed'.

I have had numerous open fires and several stoves. There are good and bad products and good and bad installations. At their best open fires work very well. At their worst (and I lived with one of those!) an open fire can be almost worse than useless.

That said, a phenomenal amount of rot is pumped out by the stove makers and installers and anyone who makes the mistake of assuming (as many seem to these days) that the figures quoted are reliable is taking a gamble.

By coincidence, just yesterday I was speaking with a former HETAS installer (he has moved on to other things) who has installed and commissioned dozens, if not hundreds, of stoves and he was telling me how, in his opinion, manufacturers fiddle the output figures of their stoves.

He had a point. I have a stove that is supposed to be rated at 14kw when running full blast. But has it ever produced the same amount of heat as seven two bar electric fires running simultaneously? No, and I doubt it ever could - whatever the manufacturer was able to come up with on a test rig.

Similarly, I have grave doubts about the reliability of the efficiency figures quoted when applied to 'the real world'.

MummyOfTwo

can anyone advise with regard to hearth tiles? i thought that i wont be able to just choose whatever i like best from the tile shop, but i wanted something square and black...

grahamc2003

A._Badger wrote: »

With respect, the problem there is 'read and believed'.

.

Well I certainly wouldn't automatically 'read and believe' anything any manufacturer put out, and manufacturers data isn't the source of anything which I have written. When looking into replacing my open fire with a stove, I read technical papers on the efficiency of stoves, and even then read them critically from a professional engineers viewpoint, with about a deep a knowledge of thermodynamics it's possible to reasonably attain. My posts are just my pov given that background, and don't solely just ooze forth randomly from my bum, and niether are they simply the views of hetas engineers, who have expertise in more practical, rather than theoretical, areas.

Of course my views may be total cack, but I'd appreciate a little more reasonaing on why they are incorrect than simply respectfully doubting them.

A._Badger

grahamc2003 wrote: »

Well I certainly wouldn't automatically 'read and believe' anything any manufacturer put out, and manufacturers data isn't the source of anything which I have written. When looking into replacing my open fire with a stove, I read technical papers on the efficiency of stoves, and even then read them critically from a professional engineers viewpoint, with about a deep a knowledge of thermodynamics it's possible to reasonably attain. My posts are just my pov given that background, and don't solely just ooze forth randomly from my bum, and niether are they simply the views of hetas engineers, who have expertise in more practical, rather than theoretical, areas.

Of course my views may be total cack, but I'd appreciate a little more reasonaing on why they are incorrect than simply respectfully doubting them.

Like several other posters here I dispute the supposedly rampant inefficiency of an open fire and the claims of greatly superior performance of a semi-closed metal box and I dispute it based on experience of both. I think it is far more variable than the theory suggests and that a well designed open fire can be extremely effective. I say that based on having used and lived with them, even though I now use a stove.

Moreover, that other black art, economics, comes into play. A lot of new posters to this forum have been bamboozled into believing that spending several thousand pounds on a stove and installation will quickly be recouped due to the inefficiencies of their fire.

An actuary specialising in life expectancy might take a different view.

highrisklowreturn

I would like a fire too and don't know whether or not I should have a fire put in or a stove. The internet, far from being a good source of info, has just confused the hell out of me. I know that to put the fire in I've been quoted around £1100, which is good and nice and simplistic - all I'm really worrying about is the colour of the surround -but stove prices vary up to maybe £2k from £800 (including installation).

I'm worried pricipally because I don't really know the difference between stoves and open fires. It seems to be broken down into the following fore me:

Fires: Cheaper, more simplistic installation, nicer to look at, easy to fuel, longer life than a stove; but on the downside allegedely reduced efficiency.
Stoves: More expensive, more complex installation, bewildering range of stoves available, poorer aesthetically compared to a fire, no knowledge of how "hot" different K stoves are; but supposedely more efficient.

Add to this that people on here like A B. say that fires can be just as good and stoves poor, and it's completly Japanese. Also would like a back boiler but I don't know again if this is a good idea as I'm clueless as to how much extra this is - for each option - and what K of stove I should go for if I want one. Also, can I have one that just does water, and not ch? And if it did CH, would the fuel use for 7 rads be ridiculous?

It's too bewildering and I'd say I've a 1/5 chance of making a good decision on this.

highrisklowreturn

Also, people say you get creosite if you burn wood and coal - but is this true for an open fire as well? I know people have been doing this for decades and they have no issue burning both on an open fire.

jonewer

grahamc2003 wrote: »

.....But none of that changes the thermal characteristics of them....

Oh, I dont deny that on average, stoves give better efficiency than open fires.

My grouse is with some of the dubious claims about how inefficient open fires are compared to how wonderfully efficient stoves are, as well as some other claims put out by manufacturers and installers. These include "you have to line your chimney or the tar will penetrate the bricks and you'll have to knock your whole house down etc." You can easily disprove this by looking at a very old house. Notice the chimneys. Fine arent they?

Look, heres some from Ightham Mote than must have been in use without a liner for about three centuries at least. and possible five or maybe more. Notice all that horrible tar penetration! Dreadful arent they!





As to losing 90% of the heat up the chimney, if 90% of the heat my little coal fire produces goes up the chimney then by golly, we need to invoke E=MC^2 to explain where all that energy is coming from!

The thing about drawing in air is also a red herring. For x units of combustion, a fire will consume x units of air. It doesnt matter if the combustion occurs in a metal box or not.

Stoves are better because you get more complete combustion because its easier to manage combustion in a closed chamber than in the open, just as theres a big difference between a well designed fireplace with a choke and baffle system compared to just a plain chimney over a fire pit.

The question is one of cost of installation and initial purchase versus the amount of fuel saved by the greater efficiency of a stove. Seeing as how an installation would cost me £4.5k, that quite a few bags of coal I'd have to burn to make the numbers add up.

jonewer

highrisklowreturn wrote: »

Also, people say you get creosite if you burn wood and coal - but is this true for an open fire as well? I know people have been doing this for decades and they have no issue burning both on an open fire.

Yes, just get your chimney swept every now and again.

The main advantage of stoves from my point of view is that you can

1. Leave them unattended with confidence
2. They can be kept in overnight.

highrisklowreturn

But what I mean is if more energy is simply being lost up the chimney than in a stove, would this not assist in clearing the chimney quicker, thereby making it less likely for creosite to form and deposit compared to a stove?

Also I take it I can burn any type of coal in a typical open fire whereas this isn't true of a stove where it always must be smokeless?

jonewer

highrisklowreturn wrote: »

But what I mean is if more energy is simply being lost up the chimney than in a stove, would this not assist in clearing the chimney quicker, thereby making it less likely for creosite to form and deposit compared to a stove?

Also I take it I can burn any type of coal in a typical open fire whereas this isn't true of a stove where it always must be smokeless?

I take issue with the assertion that more heat goes up the chimney but the contrary point is that because stoves achieve more complete combustion, theres less to stick to the chimney in the first place.

You dont always have to burn smokeless but different manufacturers have different rules about what should or shouldnt be burnt and burning something you shouldnt might void warranties or insurance if something goes wrong.