Why can't I measure temps on the glass?

[newatthis]

Love our new IR thermometer, which is showing that the magnetic thermometer was undermeasuring by at least 100 degrees on our Oslo. But with our insert, exactly why can't I measure on the glass? I have not understood the threads involving placing a thermometer on an insert flue, and don't think we are up to that kind of modification anyway.

 

[DougA]

First, you don't know if it's reading off the glass or through the glass into the fire. Second, the glass is a poor indicator of what the stove is doing and that is more important. Third, the reading off glass are very inconsistent. Even readings off the cast iron door will be better but you should be able to read anywhere on the top and get more accurate readings.

What are you specifically wanting to know about flue temp readings? If you have an IR, you probably are better off reading the stove and not the flue.

Just my opinion.

 

[newatthis]

Well, if I can't use the IR on the glass, then that leaves the narrow cast iron frame around the glass to measure. And I am getting mid to high 200s at the frame. Which doesn't seem accurate. Just looking for something to measure.

 

[prezes13]

I have a flush insert with IR I take a read just above the door. Not the door frame. I think that this number is 150-200 less what the stove top is.

 

[Ram 1500 with an axe...]

I have a large glass area, I measure the side bricks to let me know what's going on in there......

 

[GeHmTS]

Just curious, what temp do you get when you read off the glass? Do you get different readings at different angles?

 

[Ram 1500 with an axe...]

The ir doesn't read glass, it goes through the glass to the next solid mass. You can try opening the door and pointing at the glass to see if it will pick up the temperature of the glass instead of the object behind the glass....

 

[branchburner]

The ir doesn't read glass, it goes through the glass to the next solid mass.

If this is true, why do all my exterior windows read around 50-60f with my IR gun?

 

[DougA]

Some glass will have a coating on it that will reflect the IR gun and give you a reading. See my post #2.

My first experience with an IR gun was years ago when a health inspector was in my (former) restaurant and was reading the walk-in freezer. It happened to be in the defrost cycle and she was reading the cardboard boxes which were warm from the heater. She said my freezer was too warm. I argued that it was just ending the defrost cycle and the boxes were not supposed to be frozen, to allow the frost to melt.
She looked at me as if I was an idiot and said, "The IR gun shoots right through the box and measures the middle of the food". No sense arguing with an inspector.
She told me to fix it and returned the next day, took readings and was happy that all was OK and that I had made the adjustments she requested. I hadn't adjusted anything! Duh!

 

[Ram 1500 with an axe...]

If this is true, why do all my exterior windows read around 50-60f with my IR gun?

Is it 50-60 degrees outside?
I'm no expert, I'm just saying that the red dot goes through the glass and the target is in the stove, not the glass....
Oh and the reason it's taking that temp is because you have no backdrop behind the glass..... That makes sense right?

 

[Woody Stover]

that leaves the narrow cast iron frame around the glass to measure. And I am getting mid to high 200s at the frame. Which doesn't seem accurate

The door frames are usually shielded by the stove body to some degree. Heheh...degree.
I thought I read something about the IRs not reading accurately on glossy surfaces...