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Author Topic: How do I reflect the maximum heat from a woodstove?  (Read 16748 times)

Offline CZARCAR

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hot stove creates convective air patterns which result in an upward airflow so the ceiling has a heat absorber to absorb the energy
stove radiates heat in all directions so will a reflective layer of foil significantly reflect the radiation back to the stove where it will reheat the stove & result in more convective heat as rising hot air?
under the stove mfrs. specify an R-1 or 2 insulation board, but wont a reflective foil be as effective [if the heating of the board is mostly [or all?] from downward radiation of heat?
thanx
« Last Edit: 18/11/2010 22:59:21 by chris »


 

Offline peppercorn

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #1 on: 17/11/2010 15:15:19 »
All this depends heavily on the type of stove doesn;t it?
W.r.t the material the stove is stood on, it is likely to have to deal with hot-spots of conducted heat (where the feet sit) as well as radiated heat.

...

I am considering making a small wood-burning stove out of one of these:

I'd like to build with (similar to) a balance flue, so I can ensure no smoke will be let out indoors.....  ???
 

Offline CZARCAR

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #2 on: 17/11/2010 15:28:18 »
All this depends heavily on the type of stove doesn;t it?
W.r.t the material the stove is stood on, it is likely to have to deal with hot-spots of conducted heat (where the feet sit) as well as radiated heat.stove is just an example of heat radiating object which can radiate in any direction i think, unlike convection which involves hot air persistent on rising.

...

I am considering making a small wood-burning stove out of one of these:

I'd like to build with (similar to) a balance flue, so I can ensure no smoke will be let out indoors.....  ???
best way to assure no smoke is to burn the wood from the top down so the flames consume the smoke better
 

Offline peppercorn

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #3 on: 17/11/2010 15:48:37 »
best way to assure no smoke is to burn the wood from the top down so the flames consume the smoke better

I was thinking the very same after seeing a simple downdraft burner online:

This goes inside a old oil barrel.

Like so.
« Last Edit: 17/11/2010 16:02:37 by peppercorn »
 

Offline CZARCAR

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #4 on: 17/11/2010 16:01:38 »
best way to assure no smoke is to burn the wood from the top down so the flames consume the smoke better

I was thinking the very same after seeing a simple downdraft burner online:

This goes inside a old oil barrel.
dont matter where the combustion air comes into the stove due to air density, the air will go to the flame. if the flame is under the wood, it'll go there
 

Offline peppercorn

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #5 on: 17/11/2010 16:24:06 »
dont matter where the combustion air comes into the stove due to air density, the air will go to the flame. if the flame is under the wood, it'll go there

It does during lighting/heating up (cold flue, etc) - otherwise there's more chance of smoke coming into the room.  Also, I prefer the idea of not relying on the the drafts in the building bringing enough oxygen in, plus a large draw can be noticed as wind chill to some degree.  Burning with cold air taken from outside is (with a well designed burner) a better use of fuel anyway.
 

SteveFish

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #6 on: 17/11/2010 16:33:44 »
CZARCAR, many years ago thin shiny metal tiles or sheets, such as polished brass with a pattern impressed into it, were all that was required to separate a close wall from a wood stove. This worked very well and adding a little insulation to protect against heating of the metal is a good idea. What if the reflective layer gets dirty?

Radiant heat from a wood stove is one of the pleasures of this style of heating. It not only warms you directly even before the room gets warm, but it warms the walls to heat the room by convection. Your idea would work well if you were making some sort of wood central air heater with the air circulated with fans or to rooms above by convection.

Steve
 

Offline CZARCAR

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #7 on: 17/11/2010 16:37:09 »
dont matter where the combustion air comes into the stove due to air density, the air will go to the flame. if the flame is under the wood, it'll go there

It does during lighting/heating up (cold flue, etc) - otherwise there's more chance of smoke coming into the room.  Also, I prefer the idea of not relying on the the drafts in the building bringing enough oxygen in, plus a large draw can be noticed as wind chill to some degree.  Burning with cold air taken from outside is (with a well designed burner) a better use of fuel anyway.
http://www.woodheat.org/outdoorair/outdoorairmyth.htm
 

Offline CZARCAR

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #8 on: 17/11/2010 16:50:41 »
CZARCAR, many years ago thin shiny metal tiles or sheets, such as polished brass with a pattern impressed into it, were all that was required to separate a close wall from a wood stove. This worked very well and adding a little insulation to protect against heating of the metal is a good idea. What if the reflective layer gets dirty?

Radiant heat from a wood stove is one of the pleasures of this style of heating. It not only warms you directly even before the room gets warm, but it warms the walls to heat the room by convection. Your idea would work well if you were making some sort of wood central air heater with the air circulated with fans or to rooms above by convection.

Steve
a convection heating of the walls of the house would require the hot air rising from the stove circulating to the walls. i tried to void this by saying the ceiling above the stove would absorb the heat, i think. if the foil gets dirty, it will absorb the radiant, paint it black & its even better.....foil is pretty slick & i have it 5" behind my woodstove & its amazing how much cooler the block chimni behind it stays without an airgap behind the foil
 

SteveFish

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #9 on: 17/11/2010 20:57:42 »
CZARCAR:

I was commenting on direct radiant heating of walls, not convection. By heating walls with radiant heat you partially avoid the problem of hot air rising (convection) and remaining near the ceiling. This has to be stirred with a fan to mix with the cold air near the floor to heat the walls and make a room comfortable.

Steve
 

Offline CZARCAR

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #10 on: 17/11/2010 21:35:49 »
CZARCAR:

I was commenting on direct radiant heating of walls, not convection. By heating walls with radiant heat you partially avoid the problem of hot air rising (convection) and remaining near the ceiling. This has to be stirred with a fan to mix with the cold air near the floor to heat the walls and make a room comfortable.

Steve
the stove's convection creates its own thermal cycling, fans arent necessary but will accentuate the flow of the convective heat , which i tried to void in the OP. ya radiant projects like flashlight?...........u @ hearth.com?
« Last Edit: 17/11/2010 21:38:43 by CZARCAR »
 

Offline peppercorn

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #11 on: 17/11/2010 22:40:40 »
http://www.woodheat.org/outdoorair/outdoorairmyth.htm
Good article CZ!  - I'm not sure I agree with it all, but -well, thanks :D
It hasn't changed my mind that using direct-air is the way to go - A properly designed stove of this type would definitely be the more efficient.  A balanced flue approach would negated the danger of unequal inlet and outlet pressure (the warm-up stage is the most risky for reverse gas flow).  I don't agree about any gasket will leak - there won't be a major back-pressure if the placement of the fire-door, etc is carefully chosen.
 

SteveFish

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #12 on: 18/11/2010 00:21:49 »
CZARCAR. A hot stove heats air near the floor. Hot air is lighter than cold air (e.g. like a hot air balloon) and will rise to the ceiling and stay there if not disturbed, and this displaces the coldest air to the floor. You end up with a warm head and cold feet because the convection currents from the heater will not stir the air. This is the same principle as why the hot water in a water heater remains at the top of the tank. This is also why a wood stove in a main floor room in a two story building with a relatively open stairway will heat the upper story while leaving the lowest rooms, where the heater is, relatively colder. Many people use ceiling fans to stir the air.

My solution is to use a wood gassification boiler in the garage to heat a 850 gallon hot water tank, and pump the hot water through pipe in the house floor (hydronic heating) to heat with radiant heat from the floor up. You can check this and the rest of what I am talking about at Hearth.com.

http://www.hearth.com/econtent/index.php/forums/viewforum/21/

Steve
 

Offline CZARCAR

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #13 on: 18/11/2010 00:47:44 »
CZARCAR. A hot stove heats air near the floor. Hot air is lighter than cold air (e.g. like a hot air balloon) and will rise to the ceiling and stay there if not disturbed, and this displaces the coldest air to the floor. You end up with a warm head and cold feet because the convection currents from the heater will not stir the air. This is the same principle as why the hot water in a water heater remains at the top of the tank. This is also why a wood stove in a main floor room in a two story building with a relatively open stairway will heat the upper story while leaving the lowest rooms, where the heater is, relatively colder. Many people use ceiling fans to stir the air.

My solution is to use a wood gassification boiler in the garage to heat a 850 gallon hot water tank, and pump the hot water through pipe in the house floor (hydronic heating) to heat with radiant heat from the floor up. You can check this and the rest of what I am talking about at Hearth.com.

http://www.hearth.com/econtent/index.php/forums/viewforum/21/

Steve
LOL call me pook THe BANNED.  this post is about radiant heat going down & affecting the underside of a woodstove. @ hearth, they give u mfrs. specs for insulation under a stove.....i say thin layer of foil will do the trick cause its reflective & no convective is gonna heat under the stove much anyway
 

SteveFish

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #14 on: 18/11/2010 04:01:39 »
There is very little heat radiated down from a very hot wood stove, you can usually hold your hand under there indefinitely. Also the a reflective layer there would have very little effect on how the stove works to heat a space.
 

Offline CZARCAR

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #15 on: 18/11/2010 21:59:51 »
There is very little heat radiated down from a very hot wood stove, you can usually hold your hand under there indefinitely. Also the a reflective layer there would have very little effect on how the stove works to heat a space.
depends how hot the stove botom is,eh. on 2nd thought, foil aint gonna work against conductive heat
 

Offline chris

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Re: How do I reflect the maximum heat from a woodstove?
« Reply #16 on: 18/11/2010 22:58:19 »
I installed a Jotul F400 wood stove in my house earlier this year. The thing is incredible. It is heating the entire house. The engineering is awe-inspiring. It admits air in a counter-current system so that what comes in is pre-warmed aver the exhaust. This throws the smoke in the firebox forwards and down so that it is re-burned with the result that the efficiency is about 80%. It knocks the pants off another stove installed in another room. Totally incredible.

Chris
 

SteveFish

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How do I reflect the maximum heat from a woodstove?
« Reply #17 on: 19/11/2010 02:25:56 »
Jotul has always excelled in every wood burning parameter, except price.
 

Offline CZARCAR

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How do I reflect the maximum heat from a woodstove?
« Reply #18 on: 19/11/2010 13:48:31 »
I installed a Jotul F400 wood stove in my house earlier this year. The thing is incredible. It is heating the entire house. The engineering is awe-inspiring. It admits air in a counter-current system so that what comes in is pre-warmed aver the exhaust. This throws the smoke in the firebox forwards and down so that it is re-burned with the result that the efficiency is about 80%. It knocks the pants off another stove installed in another room. Totally incredible.

Chris
cooling of the fluegas topic is fun. i love the MAGIC HEAT design
 

Offline chris

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How do I reflect the maximum heat from a woodstove?
« Reply #19 on: 19/11/2010 17:56:41 »
Jotul has always excelled in every wood burning parameter, except price.

Agreed! Jotul are very expensive; however, the cheaper makes are so inferior that you end up burning up the price difference - in terms of extra fuel consumed - in about 1 season.

There's no way the other stove I've got, which is output rated similarly to the Jotul but cost about half as much, can keep up. I'd be having to flog the other stove to within an inch of its life - thus sacrificing efficiency in the process - to get the kind of heat output I do from the Jotul for the volume of fuel burned. It's just a dream machine. I am totally converted...

Chris
 

SteveFish

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How do I reflect the maximum heat from a woodstove?
« Reply #20 on: 19/11/2010 23:41:08 »
Chris, agreed. This is why I have a $7K Tarm wood gassification heater. Steve
 

Offline chris

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How do I reflect the maximum heat from a woodstove?
« Reply #21 on: 19/11/2010 23:46:35 »
Sounds interesting - but does it look nice in the living room? My Jotul does!
 

Offline CZARCAR

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How do I reflect the maximum heat from a woodstove?
« Reply #22 on: 20/11/2010 00:50:32 »
so how are the tarm & the jotul similar?
 

SteveFish

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How do I reflect the maximum heat from a woodstove?
« Reply #23 on: 20/11/2010 01:19:33 »
Chris, the Tarm is in the garage. I am considering a small wood burner for the living room just because I love wood heaters and I also have a wood cook stove, but after 45 years of mess in the house from wood and ash cleaning, and the added benefit of having year round domestic hot water without fossil fuels, and the future possibility of integrating a solar water heater into the system, I decided to made a change. I have friends who have done this and they are ecstatic.

CZARCAR, the answer to your question is that they both burn wood, not expensive fossil fuels. And, at least in my case, free firewood is readily available.

Steve
 

Offline chris

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How do I reflect the maximum heat from a woodstove?
« Reply #24 on: 20/11/2010 09:52:33 »
Anyone noticed, ironically, that this folder has now set itself alight as a "hot topic" ?!

Chris
 

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How do I reflect the maximum heat from a woodstove?
« Reply #24 on: 20/11/2010 09:52:33 »

 

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