westside said:
A) IR guns are notoriously finicky about distance/angle/color/texture of target. Unless calibrated for that shot, I would think your numbers are suspect.
B) I would be WAY more worried about the no-lid ash can you are using, myself.
Safe drywall temps
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A) IR guns are notoriously finicky about distance/angle/color/texture of target. Unless calibrated for that shot, I would think your numbers are suspect.
B) I would be WAY more worried about the no-lid ash can you are using, myself.
Battenkiller said:westside said:
Better safe than... you know.
BTW, don't go trusting your hand to act as a replacement for an IR gun. The way that skin perceives temperature is pretty complex. In a simplified explanation, it senses the rate of heat transfer, not the actual temperature itself.
Water can't be tolerated much beyond 115-120ºF for very long because water holds a lot of heat and it directly touches every pore in your skin. Aluminum foil OTOH can be held in the hand right out of a hot oven because there is very little heat contained in it because it has so little mass. Touch your cast iron stove at the same temp and you'll get zapped pretty good.
Insulating materials have there own properties that can deceive you. Wet wood is a fair conductor of heat, so it will feel hot at 150º, but dry wood won't feel hot at all at that temp because it is a superior insulator. I have had my firewood hit 145º at the recommended 3' side clearance for my stove. I could hold the back of my hand against it all day long.
Charcoal is an even better insulator. To prove this point to myself, I went down to the stove a few hours ago to check the surface temp of my coal bed. I got a reading of 225º. I put the sensitive back of my hand against and it just felt warm. I dusted off the fly ash and stirred the coals up a tiny bit and got a reading of 375º. Unbelievably, I was able to place the back of my hand on the coal bed without getting burned. This is the real secret of Indonesian fire walkers (that and a couple liters of coconut hooch).
In my physics text I once saw a photo of a cube of ultra-high insulating space age ceramic. It had a measured surface temp of 2500ºF, but the tech was holding it by the corners with his bare fingers.
Get an IR thermometer. They're dirt cheap now, and they work. It'll inform you a hundred times more than those stupid moisture meters everybody's using to give themselves a nervous breakdown about their seasoned wood.
Great points
Dakotas Dad said:
C'mon, these things are used for numerous industrial purposes all the time, from automobile diagnostics to food service inspections. It's only been very recently that consumer grade instruments have come out. Yes, like any tool they need to be used with intelligence. If you can't learn to use an IR gun properly, better stay away from putting a metal box full of burning wood in your living space.
Forget about color, it's basically irrelevant with IR. Color is based on visible light. The only thing that matters with IR is emissivity. Unless you are measuring a highly polished metallic surface, chances are the object has an emissivity of .90-.95 (a perfect IR emitter would be 1.0, but doesn't really exist outside of quantum physics theory). Flat-black stove paint, white enamel - both very close to each other (thankfully for owners of white stoves). Most consumer guns are calibrated for an emissivity of .95 for that reason. My gun has adjustable emissivity, but I don't have a clue what the emissivity of the various objects in my home are, so I just use the default .95. If I ever have to take the temp of a highly polished aluminized surface, I'll look it up and set the gun for that.
Angle sensitivity, yes... but that's a property of the IR radiation itself, not the measuring device. Short of it is, get a straight shot at the surface. A few degrees off won't make a hoot of difference.
Distance? Well, if you use it within its specs, distance is not important. But it is a mistake to think that the red dot has you on target when you are two inches away because you are ignoring the phenomenon of parallax error. Back up a foot or so and the problem disappears. Same thing for long distances. You can't take a reading of the edge of your stove from across the room with a gun that has a D:S ratio of 6:1 because it will be measuring a spot as big as the stove itself. Move closer and direct the lens of the unit (not the laser dot) directly at the target.
By knowing the specs on your gun and the size of the spot you intend to measure, you can figure out how to get a spot on (pun intended) reading.
Some of you folks might also want to do an experiment. Build you a good fire outside....and stick some drywall right close to that fire. Heck, even try putting some in the fire. Now those studs are a different kettle of fish.
Backwoods Savage said:
Ok - so have some fun. "Frame" some studs to the drywall, then lay the drywall on top of the fire (or next to it) with the studs away from the fire. Observe, take photos and video and report back. Might be interesting to see just how long it takes for anything remarkable to happen.
I know - a single fire is not the same thing as 20 years of exposure to moderately high temperatures, but still it might be interesting for those that have time for such games.
Ah shucks . . . I'm just a dumb firefighter . . . I still say you don't need an IR gun or need to even stick your hand on the wall to determine what is too hot . . . just read the instructions and install it per the manufacturer's specs . . . they came up with those numbers in the manual for a reason . . . I really don't think they just picked a few numbers and figured those clearance numbers were good enough . . . but again . . . if you want to err on the side of caution just go out a little more than the minimum.
firefighterjake said:
You forget - this is the internet! Everyone here is an expert and all others are fools. Unless I can prove it to myself it isn't true! You are asking me to trust all those so-called experts that have actually gone to school and studied these topics for much of their lives and are taking on the financial and personal liability of making a mistake over my designing my own experiment? Come on now! Obviously there is some sort of conspiracy (isn't there one in everything discussed on the internet?) involved in how those numbers for clearances were devised. Secretly they must have been calculated such that at some date (I think it is in 2012 isn't it?) all walls near stoves will burst in flames at the same time.
Battenkiller said:
I do know exactly how to use one. Most people who own one don't. Like most gadgets, they drop in the batteries and start shooting stuff.
Actually.. while helping a friend of mine work on his Phd in Engineering, we did a bunch of experiments with various grades and types of IR thermometers, and "price points" They all were sensitive to the variables I mentioned/listed, some more than others. We used targets that varied on all the points I listed, but all at an exact known temp. Emissivity varies a whole lot more than most people think. But the point I was trying to make, is he is shooting a wood wall, at an angle, at whatever distance he can get with his 6" clearance. These can all effect the reading, and I would not use that number as an absolute/point of worry.
Dakotas Dad said:
DD, didn't mean to offend you, I was rushing out of here and shouldn't have posted so hastily.
I don't doubt for a minute what you are telling us, but I really would love to see that data. I'm very interested in that sort of stuff, strictly on an academic basis.
In looking over some emissivity figures for common materials, it appears that there are some sleepers in there that one should know need to be corrected for. If I ever need my IR for critical work of any sort, I'll be sure to check the tables and not be so smug about that .95 coefficient.
Surface texture does appear to be key player as well, but mostly as emissivities are affected by highly polished metallic surfaces. However, looking up granite (I assume polished) I found coefficients in the .45-.50 range. This makes me strongly suspect polished soapstone, a rock I can't find a number for. If it's at all like granite, rock stove owners might as well toss their non-adjustable IRs in the trash. For the rest of us mere mortals (as in non-rock stove owners), porcelain, painted cast and steel (painted just about anything), most glass and wood are all in the "safe" range of around .90 to .95. At all emissivities, however, I feel they are at least a useful reference point tool when used consistently on the same material.
Anyway, thanks for bringing this to my attention, and I apologize again if I offended you.
It sure was a lot easier and calmer heating with wood back before I could read all of this stuff.
Cut tree
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Cut tree
Burn tree
Don't put magazine rack on hearth
Day two update.
Thanks for all the feedback so far. Great discussion.
I have the stove at a decent operating temp-- flue temp at 18 inches from the stove is 425F.
There are parts of the wall that I can't hold my hand against longer than 5 seconds.
It might be a safe temp but I am uncomfortable with it. We have the tile guy coming over next week to tile the back wall. He will only work with Hardibacker, so I picked-up three sheets of 1/2 inch, and 35 sqft of slate tile.
My next question is about the back wall. I believe I need a 1 inch gap, as the Hardibacker will simply transfer the heat. Is this correct? Right now I have the sheets resting just off the wall, and the back feels much cooler.
With Hardibacker, can I cut 3 inch strips, screw them into the studs, and mount the Hardibacker board to those, then have the slate put on?
Thanks for all the feedback so far. Great discussion.
I have the stove at a decent operating temp-- flue temp at 18 inches from the stove is 425F.
There are parts of the wall that I can't hold my hand against longer than 5 seconds.
It might be a safe temp but I am uncomfortable with it. We have the tile guy coming over next week to tile the back wall. He will only work with Hardibacker, so I picked-up three sheets of 1/2 inch, and 35 sqft of slate tile.
My next question is about the back wall. I believe I need a 1 inch gap, as the Hardibacker will simply transfer the heat. Is this correct? Right now I have the sheets resting just off the wall, and the back feels much cooler.
With Hardibacker, can I cut 3 inch strips, screw them into the studs, and mount the Hardibacker board to those, then have the slate put on?
unhdsm said:
If you are uncomfortable with it, then yes, you need to do what makes you comfortable.. What do you intend to cut three inch strips from? the hardibacker? No need for the spacer to be 3" wide, or a strip, and since you are doing it only to make yourself feel better, not to meet any needed requirement, my guess is you can do it anyway you want.. as long as you don't do something that might violate the non-combustible rule or something... A 1" airspace would be what was needed, if you NEEDED the protection. Open at the top and bottom, so there can be airflow. Ceramic spacers are available, and would transmit less heat.. since you are going to be putting mortar over it, don't use regular drywall screws, they will rust over time..
rambling.. need.. breakfast...
Fascinating. The guy at Home Depot told me drywall screws won't be a problem because it's not a bathroom or kitchen (ie: exposed to moisture). So I have two boxes of 3 inch drywall screws sitting here.
unhdsm said:
two boxes?? are they boxes of 20? I think you have plenty of screws.. after thinking about it, they will probably do fine. I just generally don't use regular drywall screws with any backer board material. The moisture from the mortar will be minimal, and a one time thing..
Did I mention I hadn't had breakfast yet?
OH, and save some money, hang the tile yourself. I swear to you it just ain't that hard.
Yes, they are the small boxes.
The tile guy is actually a family member who gives a great price. I do have to call him and make sure he is comfortable having it spaced out from the wall. Although I could do it, it would take me so much longer. Generally I am a "do it yourself-er".
Thank for the feedback again. Normal drywall screws it is!
The tile guy is actually a family member who gives a great price. I do have to call him and make sure he is comfortable having it spaced out from the wall. Although I could do it, it would take me so much longer. Generally I am a "do it yourself-er".
Thank for the feedback again. Normal drywall screws it is!
As Dakotas said, you don't NEED the air space or the hardibacker for that matter. Since the stove already meets the clearances to the drywall it could stay as-is, or you could layer hardibacker and tile directly on the drywall. The Hardibacker has an R value of 0.22 (I think) so even without the air gap it will keep some heat off the drywall.
For the best heat protection you will want a 1" ventilated air gap open on the top and bottom.
For the best heat protection you will want a 1" ventilated air gap open on the top and bottom.
I am doing an experiment right now. I leaned the hardibacker panels against the wall with a (roughly) one -inch gap and taped a digital thermometer probe on the hottest spot of the wall, and have had the stovetop running at 450F for two hours or so. The wall behind the hardibacker made it to 115F. I don't know the temp of the front of the hardibacker but it is (obviously) much hotter. I did not hear back from tileguy about putting the hardibacker on 1 inch spacers but I am hoping he will be okay with that (meaning that it will hold-up to the install and weight of the slate tiles).
Digital IR thermometer that I bought at Harbor Freight, $30 or 40 bucks. I use it on occasion, but I have an insert jammed into a firebrick lined fireplace. I have three feet of brick surrounding my insert on both sides and above. I actually use the IR to see if those bricks are warm and radiating into the house.
And the space shuttle didn't explode. Plenty of experts on that one.Slow1 said:firefighterjake said:
You forget - this is the internet! Everyone here is an expert and all others are fools. Unless I can prove it to myself it isn't true! You are asking me to trust all those so-called experts that have actually gone to school and studied these topics for much of their lives and are taking on the financial and personal liability of making a mistake over my designing my own experiment? Come on now! Obviously there is some sort of conspiracy (isn't there one in everything discussed on the internet?) involved in how those numbers for clearances were devised. Secretly they must have been calculated such that at some date (I think it is in 2012 isn't it?) all walls near stoves will burst in flames at the same time.
Battenkiller said:
Took a bit of looking, but I found this and I thought I'd follow up on it. As you can see, while granite has an emissivity of .45, soapstone is at .95, which is the emissivity that almost all IR guns use as a default. This info was found on page 129 of the book, "Masonry Heaters" by Ken Matesz. So you soapstone guys can trust your cheap IR guns, they are a perfect match for your stoves. Just make sure to get close enough, and to hold the gun perpendicular to the surface while taking the reading.
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newtothis said:And the space shuttle didn't explode. Plenty of experts on that one.Slow1 said:firefighterjake said:
You forget - this is the internet! Everyone here is an expert and all others are fools. Unless I can prove it to myself it isn't true! You are asking me to trust all those so-called experts that have actually gone to school and studied these topics for much of their lives and are taking on the financial and personal liability of making a mistake over my designing my own experiment? Come on now! Obviously there is some sort of conspiracy (isn't there one in everything discussed on the internet?) involved in how those numbers for clearances were devised. Secretly they must have been calculated such that at some date (I think it is in 2012 isn't it?) all walls near stoves will burst in flames at the same time.
I would argue that there is a world of difference between a big metal box that does not move and only has two to three moving parts vs. a space shuttle which has many more parts and is subjected to a lot of high stress factors -- i.e. gravity, extreme heat, speed, etc.
Besides . . . woodstoves have been around for a very, very long time . . . and understanding the methods of heat transfer have been known . . . for a much, much longer time than the shuttle has been flying.
Keith Briggs
New Member
Just another data point. I've been running my quad 5100i (insert mind you) and underside of the white oak mantel is drywall. Its 207 degrees F right now (inexpensive kintrex IR thermometer - great toy that you'll use more than you think). No blisters in the paint after two years running. I can only hold my hand on it for a split second. I was going to tile it but never got around to it. Now I don't worry about it. Center glass of the stove is reading 850 degrees F. It is interesting because the white oak has an r-factor of 0.86 per inch and 5/8 drywall is 0.56 (0.83 per inch) the temps should be the same but the bottom of the oak front board is 10 degrees cooler and drops to 120 3" up. Anyway, there's been no discoloration in the drywall or the oak. Right now its 38 outside, 75 inside. It heats over 3000 sq ft in Evergreen, CO and I still have 125 gallons in the propane tank I had "filled" (400 g) last June. Mostly used during winter vacations & sometimes in the basement. Anyway, I have no concerns with my setup.
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