Flipping logs over on the fire

[ScienceNostalgia101]

So when I use the outdoor fireplace, I often like to flip the logs upside down partway through their burning so that i have fresh unburned wood in direct contact with the flames at least twice as often. An uncle of mine once told me this actually does more harm than good to how well it burns, because the heat drives the moisture to the top of the log, and flipping it would cause the flames to be in contact with wetter wood instead of drier wood. I tried Googling this but I haven't found anything on this either way. To those of you better versed in chemistry does this make sense? Why or why not?

[zapatos]

I'm not familiar with 'heat driving moisture'. I suppose as moisture turns to steam it expands in all possible directions so you "may" get more moisture in the top of the log, but the heat should be boiling that off too. 

Bottom line is that all of the water in the log has to boil off, whether you do it by turning the log or not.

I think you need to define what you mean by "harming" how well the log burns. Do you mean how fast? (if so, is fast good or bad?) Average temperature? Kind of vague.

From many years of experience I'd say a turned log burns faster than one that is not turned.

[Peterkin]

I think if you turn it, you expose more of the already burning fuel to air to make it burn faster and hotter, not unlike blowing under it. 

[Phi for All]

15 hours ago, zapatos said:

I think you need to define what you mean by "harming" how well the log burns.

Exactly. For an outdoor fireplace, it would seem the main factors are heat, light, and duration, all to provide various ambiances (I'm assuming this fire isn't for cooking). You can adjust these by configuring your fire differently, or by using different woods. Soft woods get started more easily, but hard woods burn longer. You need some context before you could say a specific treatment was harmful to a particular process. 

15 hours ago, zapatos said:

Bottom line is that all of the water in the log has to boil off, whether you do it by turning the log or not.

I'm not a big wood burner, but isn't this why firewood should be seasoned before burning, to dry it out as much as possible? 

[StringJunky]

43 minutes ago, Phi for All said:

Exactly. For an outdoor fireplace, it would seem the main factors are heat, light, and duration, all to provide various ambiances (I'm assuming this fire isn't for cooking). You can adjust these by configuring your fire differently, or by using different woods. Soft woods get started more easily, but hard woods burn longer. You need some context before you could say a specific treatment was harmful to a particular process. 

I'm not a big wood burner, but isn't this why firewood should be seasoned before burning, to dry it out as much as possible? 

I would think larger logs are less amenable to to turning over if it's relying on a hot core to keep burning... once you open it up it could cool too much and lose flammable vapour production.

Edited July 25, 2021 by StringJunky

[zapatos]

3 hours ago, StringJunky said:

I would think larger logs are less amenable to to turning over if it's relying on a hot core to keep burning... once you open it up it could cool too much and lose flammable vapour production.

With an outdoor fire, once the fire is established the wood is setting on a bed of coals. Turning the wood over puts fresh fuel in contact with the hot coals.

4 hours ago, Phi for All said:

I'm not a big wood burner, but isn't this why firewood should be seasoned before burning, to dry it out as much as possible? 

Absolutely. Burns hotter and cleaner, and if burning in an indoor fireplace unseasoned wood leads to creosote buildup and a potential fire hazard in the flue. But even seasoned wood might have 20% water content.

[ScienceNostalgia101]

To be clear, the goal for my purposes is to have as many kJ of heat per litre of smoke; or alternatively, as few litres of smoke per kJ of heat; as possible.

[geordief]

58 minutes ago, ScienceNostalgia101 said:

To be clear, the goal for my purposes is to have as many kJ of heat per litre of smoke; or alternatively, as few litres of smoke per kJ of heat; as possible.

As others have noted ,you can season your logs as much as possible (I believe 2 years may be common in Germany)

 

I sometimes quick dry dry my logs (overnight or for an hour or so with twigs)  in the oven  and get a hell of a blaze very quickly.

 

Most of my heat goes up the chimney but that is  not too much of a concern for me as I have a ready supply of trees (but not of cash).

I often stare at the fire and wonder what is the best tactic to get the maximum heat  from what I have on it.

 

My first idea was to put the fuel to the back  as I felt that it would burn better but my neighbour was insistent I should bring it to the front . I am no wiser on that score.

 

If you keep turning the logs  you should incorporate more oxygen,I'd have thought though with big logs that is less obvious.

 

We used to have a "dampner" (?)in my old house  that you could draw across the chimney to keep the heat in the room when the smoke was gone out of the fire  but I doubt they are simple to put in once the chimney is made.

Edited July 26, 2021 by geordief

[TheVat]

105 is tomorrow's predicted high here,  with a blood red sun from the wildfire smoke that's wafting from Oregon to Boston,  so burning wood has lost some of it's fun and cozy feeling.   The world doesn't need more polycyclic aromatic hydrocarbons and PM 2.5 atm.   

 

Sincerely,   the fireside Grinch 

[zapatos]

1 hour ago, ScienceNostalgia101 said:

To be clear, the goal for my purposes is to have as many kJ of heat per litre of smoke; or alternatively, as few litres of smoke per kJ of heat; as possible.

Then it shouldn't matter much whether you flip or not. Just make sure you maintain plenty of air flow to allow for complete combustion. As long as you have good airflow the only thing flipping the wood does is change how quickly the heat is generated.

[exchemist]

20 hours ago, StringJunky said:

I would think larger logs are less amenable to to turning over if it's relying on a hot core to keep burning... once you open it up it could cool too much and lose flammable vapour production.

I agree with this.

It has to be borne in mind that charcoal, which is what is left after the volatiles have been driven off and burnt, requires a very high temperature to make it burn. If you turn a partly burnt log so that the charred side is upwards, the charcoal will lose heat and may stop burning. If you want to burn the logs completely to ash you ned to maintain a high temperature in the centre of the fire. Disturbing the logs will increase the temporary heat radiation from the fire but by the same toke will cause it to lose temperature. You may end up with less heat in the end, if the result is a lot of unburnt charcoal left behind. Also, if the logs still have some moisture, you risk actually putting the fire out, by diverting even more heat into evaporating the moisture.  

I think it is best to keep a really hot centre to any wood fire, which is best achieved by periodically moving the logs closer together as they burn, and not by turning them.  

[zapatos]

6 minutes ago, exchemist said:

I agree with this.

It has to be borne in mind that charcoal, which is what is left after the volatiles have been driven off and burnt, requires a very high temperature to make it burn. If you turn a partly burnt log so that the charred side is upwards, the charcoal will lose heat and may stop burning. If you want to burn the logs completely to ash you ned to maintain a high temperature in the centre of the fire. Disturbing the logs will increase the temporary heat radiation from the fire but by the same toke will cause it to lose temperature. You may end up with less heat in the end, if the result is a lot of unburnt charcoal left behind. Also, if the logs still have some moisture, you risk actually putting the fire out, by diverting even more heat into evaporating the moisture.  

I think it is best to keep a really hot centre to any wood fire, which is best achieved by periodically moving the logs closer together as they burn, and not by turning them.  

I'm a bit confused by this. If you turn a log over, instead of one side of the log burning you now have two sides of the log burning. Even if the originally burning side slows combustion, the newly burning side will soon be burning at the rate of the originally burning side (even faster for a while).

[geordief]

9 minutes ago, zapatos said:

I'm a bit confused by this. If you turn a log over, instead of one side of the log burning you now have two sides of the log burning. Even if the originally burning side slows combustion, the newly burning side will soon be burning at the rate of the originally burning side (even faster for a while).

I have often  noticed that disturbing a fire causes it to lose momentum .The unburned  part you expose to the fire takes a little while to get going.

Also ,as @exchemist said the charcoaled part of the wood stops burning  very quickly when turned away from the flame.

 

To keep the fire burning strong my tactic is often to add small pieces in the way of the flames (but even this will slow the fire down until they catch)

Edited July 26, 2021 by geordief

[exchemist]

23 minutes ago, zapatos said:

I'm a bit confused by this. If you turn a log over, instead of one side of the log burning you now have two sides of the log burning. Even if the originally burning side slows combustion, the newly burning side will soon be burning at the rate of the originally burning side (even faster for a while).

It takes a lot of heat input to get the fresh side of the log up to burning temperature, which cools the centre of the fire, while the burned side is radiating out into the room and ceasing to burn. And what is worse is you now have cold charcoal which has to be reheated somehow before it can be made to burn once more.

But I suppose the way it works out may depend on what kind of log you are burning. Some woods, from coniferous trees, are full of volatiles that burn very readily, so the fresh surface of logs from these may catch relatively quickly, whereas (speaking from experience) others take ages to catch light and some can barely be made to burn at all. 

But the most intense heat comes from burning charcoal, after the yellow flames have died away. 

Edited July 26, 2021 by exchemist

[StringJunky]

1 hour ago, geordief said:

As others have noted ,you can season your logs as much as possible (I believe 2 years may be common in Germany)

 

I sometimes quick dry dry my logs (overnight or for an hour or so with twigs)  in the oven  and get a hell of a blaze very quickly.

 

Most of my heat goes up the chimney but that is  not too much of a concern for me as I have a ready supply of trees (but not of cash).

I often stare at the fire and wonder what is the best tactic to get the maximum heat  from what I have on it.

 

My first idea was to put the fuel to the back  as I felt that it would burn better but my neighbour was insistent I should bring it to the front . I am no wiser on that score.

 

If you keep turning the logs  you should incorporate more oxygen,I'd have thought though with big logs that is less obvious.

 

We used to have a "dampner" (?)in my old house  that you could draw across the chimney to keep the heat in the room when the smoke was gone out of the fire  but I doubt they are simple to put in once the chimney is made.

The most efficient, I think, is to have the fire place projecting  into the room where the metal roof is exposed above it. Much more high quality convected heat will pour into the room instead of predominantely radiant heat of a typical open fire. You'll find that the hot zone is not just local around the fire as well... it's all over.

Edited July 26, 2021 by StringJunky

[zapatos]

In my experience as a fire sits undisturbed, the flames slowly reduce and the heat level goes down. Given enough time the majority of logs will be consumed. If I want more flame and thus more heat I turn the logs over. Perhaps we are talking about different aspects of the burning process, but I see people 'instinctively' picking up a long stick to poke at the fire and expose more of the unburned fuel to the coals.

[geordief]

32 minutes ago, StringJunky said:

The most efficient, I think, is to have the fire place projecting  into the room where the metal roof is exposed above it. Much more high quality convected heat will pour into the room instead of predominantely radiant heat of a typical open fire. You'll find that the hot zone is not just local around the fire as well... it's all over.

Yes I see that. Actually in my case the first thing I would do is to draught proof the room.

All my windows and all my doors  are draughty but I have no cash to address the problem (that I just live with)

😅

[Phi for All]

9 minutes ago, geordief said:

All my windows and all my doors  are draughty but I have no cash to address the problem (that I just live with)

Have you made any draught snakes? Fill some old tube socks (or sew up the arm from a long-sleeved shirt) with dry rice, making a "snake" you can put at the base of draughty windows and doors. Cheap and effective, and you don't have to keep flipping them over.

[StringJunky]

1 minute ago, Phi for All said:

Have you made any draught snakes? Fill some old tube socks (or sew up the arm from a long-sleeved shirt) with dry rice, making a "snake" you can put at the base of draughty windows and doors. Cheap and effective, and you don't have to keep flipping them over.

First time I saw one of them, probably 3 or 4,  I thought my grandad said it was a 'giraffe excluder' and kept out giraffes! The joys of deafness. "How's a giraffe going to get under that little gap?"

[Phi for All]

2 minutes ago, StringJunky said:

First time I saw one of them, probably 3 or 4,  I thought my grandad said it was a 'giraffe excluder' and kept out giraffes! The joys of deafness.

Damned effective excluder, too. Bet you never had any giraffe problems growing up. Those snakes are an obvious choking hazard!

5 minutes ago, StringJunky said:

"How's a giraffe going to get under that little gap?"

Limbo! How low can you go?

[geordief]

18 minutes ago, Phi for All said:

Have you made any draught snakes? Fill some old tube socks (or sew up the arm from a long-sleeved shirt) with dry rice, making a "snake" you can put at the base of draughty windows and doors. Cheap and effective, and you don't have to keep flipping them over.

Oh yes ,tried that  but there are too many  points of entry .Even the front door needs replacing  and ,in the drawing room we have an archway rather than an actual door.

All the  (sash) windows are very old  and don't meet flush at top middle or bottom.

 

Great for Covid times,mind you😆

[TheVat]

Due to our bitter winters here, it's hard to find houses that leak to that degree.  If a house does leak that badly, selling off a family member to fund the renovation is usually considered.  BTW, the snakes are sometimes called "draft dodgers" here in the States.  

The cheapest fast fix I know for draughts (I really prefer the Brit spelling, because it reminds me of enjoyable libations) is the window film you put on the inside, using double-sided tape, and then making taut with a hair dryer.   This is okay for windows you don't plan to open in the warmer weather.  The plastic will usually adhere pretty well for several years, and then you do it all over again.  It's way cheaper than buying storm windows or getting newer triple-glazed argon-filled windows (which have grown insanely expensive lately, like a lot of other construction supplies).   I realize this is straying a bit from the topic of chemistry.  Argon gas doesn't even have much chemistry, being noble. 

Edited July 26, 2021 by TheVat
dfdgsdfefs

[iNow]

50 minutes ago, TheVat said:

BTW, the snakes are sometimes called "draft dodgers" here in the States.

The other name for those is "Donald Trump." #bonespurs

[Phi for All]

8 minutes ago, iNow said:

The other name for those is "Donald Trump." #bonespurs

And now I have a company making red Draft Dodger window snakes for the anti-draft movement. They're printed with "Make America Calm Again", and they're filled with shredded voter ballots. Available in Small, Medium, and Yuge.

[exchemist]

2 hours ago, zapatos said:

In my experience as a fire sits undisturbed, the flames slowly reduce and the heat level goes down. Given enough time the majority of logs will be consumed. If I want more flame and thus more heat I turn the logs over. Perhaps we are talking about different aspects of the burning process, but I see people 'instinctively' picking up a long stick to poke at the fire and expose more of the unburned fuel to the coals.

Yes, but to get it going again the thing to do is move all the burning surfaces closer together, and then it will heat up and burn more fiercely again.