Paul Haigh on mon 5 nov 07
At the risk of being verbally abused here, I want a little advice on chimney temps. I have a 40 cu ft. wood kiln with a 23" wide (od) hardbrick chimney- currently tight, with clay/sand mortar skim between all bricks. It passes through a roof at about 10-13' (on one sloped side). 3 sides of the chimney have 12" clearance to the first wood, and one is only 7" from the ridge. The roof is just a roof- open on all sides, with metal roofing and a ridge vent, no gable closures. The chimney is 13" from the end, and there's a big hole with raised welded frame with roofing over it to provide a LOT of ventilation there.
All closest beamse have been given a loose layer of aluminum flashing. The ridge beam (close side) has this arrangement: brick, flashing, 1" Kaowool, 1.5" firebat, 1" kaowool board, flashing, spare aluminum roofing, then 2-3" air gap to the ridge. About 8' of the chimney will be insulated thusly. The other three sides will be similarly insulated- sans the kaowool board.
I had thought about doing a passive counter-current cooling system- using the air rise next to the chimneyy to draw air down in a gap and cool the roofing (thr ridges act to creat an air gap, if installed upside down), but as I'm working alone- it's nigh impossible to do what I have already.
Aside from the general "don't use wood" comments, do you think this will work out?
David Hendley on wed 7 nov 07
Your protection system for the wood rafters and beams sounds more
than adequate. The air gap is the most important part of the sandwich.
Just remember to periodically check the insulation and metal shields.
It also wouldn't hurt to climb up and actually feel the wood with your
bare hand at the end of a firing. It can be warm, but should not
be hot to the touch.
David Hendley
Maydelle, Texas
david(at)farmpots(dot)com
http://www.farmpots.com
----- Original Message -----
> At the risk of being verbally abused here, I want a little advice on
> chimney temps. I have a 40 cu ft. wood kiln with a 23" wide (od)
> hardbrick chimney- currently tight, with clay/sand mortar skim between all
> bricks. It passes through a roof at about 10-13' (on one sloped side). 3
> sides of the chimney have 12" clearance to the first wood, and one is only
> 7" from the ridge. The roof is just a roof- open on all sides, with metal
> roofing and a ridge vent, no gable closures. The chimney is 13" from the
> end, and there's a big hole with raised welded frame with roofing over it
> to provide a LOT of ventilation there.
>
> All closest beamse have been given a loose layer of aluminum flashing.
> The ridge beam (close side) has this arrangement: brick, flashing, 1"
> Kaowool, 1.5" firebat, 1" kaowool board, flashing, spare aluminum roofing,
> then 2-3" air gap to the ridge. About 8' of the chimney will be insulated
> thusly. The other three sides will be similarly insulated- sans the
> kaowool board.
gsomdahl on wed 7 nov 07
Get an oven thermometer and mount it on the wood beam.
David Hendley wrote:
> ...
> It also wouldn't hurt to climb up and actually feel the wood with your
> bare hand at the end of a firing. It can be warm, but should not be
> hot to the touch.
>
--
This is a post only account. Send replies to "gene" at my ".com" domain named "somdahl".
Eva Gallagher on wed 7 nov 07
What I great idea and so simple! I have the same dilema - only 8" from the
centre ridge pole and after my first firing which was a rather short 12
hours or so and during which it was extremely windy and cold I could detect
no heat lower down on the rafters, but come summertime when the temp is in
the 90's and no wind and longer firing it might be a different matter.
Eva Gallagher
Deep River, Ontario
----- Original Message -----
From: "gsomdahl"
To:
Sent: Wednesday, November 07, 2007 9:07 AM
Subject: Re: Chimney safety
> Get an oven thermometer and mount it on the wood beam.
>
> David Hendley wrote:
>> ...
>> It also wouldn't hurt to climb up and actually feel the wood with your
>> bare hand at the end of a firing. It can be warm, but should not be
>> hot to the touch.
>>
> --
>
> This is a post only account. Send replies to "gene" at my ".com" domain
> named "somdahl".
>
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>
Tom at Hutchtel.net on wed 7 nov 07
Don't think this is a good idea. A thermometer on the stack is interesting,
but what counts is the temp of the wood....and the condition of the wood
over time. I've posted this before.
We had a stack that went about 14" away from a wood roof structure. I
shielded it with 1" of fiber board. Watched the thermometer on the stack
until I got bored and no longer looked at it.
David's suggestion was the closest, get up there and touch it. Then
consider that the wood's temperature of ignition goes DOWN with every
firing. The wood actually changes chemically. Ultimately it reaches the
point where it will ignite at about 160 degF. Are you willing to risk when
it will reach that. PLEASE, go talk to your fire marshal or fire department
chief. Ask him/her about what starts fires.
8" clearance will just about guarantee a fire at some point, even with
shielding. What you'll find is that nothing appears to be happening and you
get lulled into complacence, just as the conditions are moving toward the
ultimate and predictable 'accident'.
When the insurance inspector asked the question, did you have anything with
the start of this fire? ...I had to answer, I had the shed built.
Subject: Re: Chimney safety
> What I great idea and so simple! I have the same dilema - only 8" from the
> centre ridge pole and after my first firing which was a rather short 12
> hours or so and during which it was extremely windy and cold I could
> detect
> no heat lower down on the rafters, but come summertime when the temp is in
> the 90's and no wind and longer firing it might be a different matter.
> From: "gsomdahl"
>> Get an oven thermometer and mount it on the wood beam.
>>
>>> It also wouldn't hurt to climb up and actually feel the wood with your
>>> bare hand at the end of a firing. It can be warm, but should not be
>>> hot to the touch.
Tom at Hutchtel.net on wed 7 nov 07
Don't think this is a good idea. A thermometer on the stack or framing is
interesting,
but what counts is the temp of the wood....and the condition of the wood
over time. I've posted this before. Also, are you willing to continue to
watch this thermometer a few hours after you get done firing at midnight?
The wood will continue to heat until the stack is cooler than it is.
We had a stack that went about 14" away from a wood roof structure. I
shielded it with 1" of fiber board. Watched the thermometer on the stack
until I got bored and no longer looked at it.
David's suggestion was the closest, get up there and touch it. And as I
said above, keep going up there after the firing is over for at least 3
hours. Then
consider that the wood's temperature of ignition goes DOWN with every
firing. The wood actually changes chemically. Ultimately it reaches the
point where it will ignite at about 160 degF. Are you willing to risk when
it will reach that. PLEASE, go talk to your fire marshal or fire department
chief. Ask him/her about what starts fires. Take this post with you to
check my facts.
8" clearance will just about guarantee a fire at some point, even with
shielding. What you'll find is that nothing appears to be happening and you
get lulled into complacence, just as the conditions are moving toward the
ultimate and predictable 'accident'.
When the insurance inspector asked me the question, did you have anything
with
the start of this fire? ...I had to answer, I had the shed built.
Subject: Re: Chimney safety
> What I great idea and so simple! I have the same dilemma - only 8" from
> the
> centre ridge pole and after my first firing which was a rather short 12
> hours or so and during which it was extremely windy and cold I could
> detect
> no heat lower down on the rafters, but come summertime when the temp is in
> the 90's and no wind and longer firing it might be a different matter.
> From: "gsomdahl"
>> Get an oven thermometer and mount it on the wood beam.
>>
>>> It also wouldn't hurt to climb up and actually feel the wood with your
>>> bare hand at the end of a firing. It can be warm, but should not be
>>> hot to the touch.
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