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Old 01-11-2011, 04:11 PM
 
Location: DFW, TX
83 posts, read 169,300 times
Reputation: 31
Default How to check the temperature of the Hot air coming out of the Vent

Is there any small gadgets to check the temperature of the Hot air coming out of the Vent. It looks like one of the vents in the bedroom seems to let very small quantity of air thus very little heat. Rest of the vents are fine with considerable about of heat to keep the place warm.

Before deciding to work on it I wanted to check the temperature of the hot air coming out of that vent. (I don't want to spend several hundreds for the tool; I am willing to check if this can be done by least expensive gadgets)

Any suggestions?

Thanks.
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Old 01-11-2011, 04:37 PM
 
Location: Cary, NC
601 posts, read 2,020,603 times
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You can use just about any temperature probe. I use a $15 indoor/outdoor thermometer with a wired lead - stick the lead up into the vent and wait a couple minutes for the temperature to stabilize.

But it really sounds like you have an air-flow issue, most likely there is a partially closed damper on the duct feeding that vent. Check the duct where it connects to the main trunk of your HVAC system, there may be a damper lever there. Another possibility is that the duct is kinked or crushed between the trunk and the vent.
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Old 01-11-2011, 04:37 PM
 
Location: Dallas/Ft. Worth, TX
1,191 posts, read 2,687,004 times
Reputation: 1926
Quote:
Originally Posted by Matt2010 View Post
Is there any small gadgets to check the temperature of the Hot air coming out of the Vent. It looks like one of the vents in the bedroom seems to let very small quantity of air thus very little heat. Rest of the vents are fine with considerable about of heat to keep the place warm.

Before deciding to work on it I wanted to check the temperature of the hot air coming out of that vent. (I don't want to spend several hundreds for the tool; I am willing to check if this can be done by least expensive gadgets)

Any suggestions?

Thanks.
Home Depot sells an inexpensive infrared thermometer it will be sufficient for what you want to do and can be used for other things as well.
Ryobi Non-Contact Infrared Thermometer - IR001 at The Home Depot
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Old 01-12-2011, 06:12 AM
 
Location: Knoxville
3,295 posts, read 10,411,264 times
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You can use an inexpensive cooking thermometer as well. That way the probe is inside the register and will tell you the temps of the air.

While infrared thermometers are a cool gadget (I own and use them), they are probably not the best tool to use to determine air temperature coming out of a register. They don't just register the temperature in the little red dot you see. They have an area of focus that gets bigger the further away you are from the target. For instance, the field might by 12" square when you are 3 feet away from the target, but could be 3 feet square when you are 10 feet away. Kind of like a flashlight, the further away you are, the wider the range of light.

While you can get a quick and dirty temp reading, a more accurate way is to use a probe type thermometer.
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Old 01-12-2011, 10:26 AM
 
6,345 posts, read 7,004,621 times
Reputation: 5523
Quote:
Originally Posted by Barking Spider View Post
While infrared thermometers are a cool gadget (I own and use them), they are probably not the best tool to use to determine air temperature coming out of a register. They don't just register the temperature in the little red dot you see. They have an area of focus that gets bigger the further away you are from the target. For instance, the field might by 12" square when you are 3 feet away from the target, but could be 3 feet square when you are 10 feet away. Kind of like a flashlight, the further away you are, the wider the range of light.
+1

Here's one RTEMP25PB, Thermometer, Infrared, Automotive Diagnosis (w/Plastic Case) that will actually show the size of the area it is measuring (it ain't cheap).

Also, a non-contact infrared thermometer will not measure air temp, only surface temp.
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Old 01-12-2011, 01:17 PM
 
Location: Austin, TX
14,314 posts, read 20,082,323 times
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Quote:
Originally Posted by dedratermi View Post
You can use just about any temperature probe. I use a $15 indoor/outdoor thermometer with a wired lead - stick the lead up into the vent and wait a couple minutes for the temperature to stabilize.

But it really sounds like you have an air-flow issue, most likely there is a partially closed damper on the duct feeding that vent. Check the duct where it connects to the main trunk of your HVAC system, there may be a damper lever there. Another possibility is that the duct is kinked or crushed between the trunk and the vent.
It could very well be that you have a duct leak as well. Typical duct leakage is 25% in an older home. That is 25% of your energy and dollars being lost to duct leaks.

The typical grey flexible ducts installed in the 1970's is now becoming brittle and easy to crack, resulting in significant leakage in those homes.
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Old 01-12-2011, 04:25 PM
 
Location: DFW, TX
83 posts, read 169,300 times
Reputation: 31
Thanks to all for your suggestions; will check on those.
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Old 01-13-2011, 09:57 AM
 
Location: Johns Creek, GA
6,647 posts, read 20,724,030 times
Reputation: 5143
Truth be known-
the temperature of the air at a register will tell you absolutely nothing! Other than what the temperature of the air at that point- again, means nothing.
A furnace creates so many btu's, the heat is transferred by way of the exchanger (loss of temp), then it's pushed through ducts of varying shapes, diameters, lengths, and insulation factors (more loss of temp, and loss of velocity). By the time it gets to a register, the air temperature could be considerably less than say a register that's only a few feet away.
ASHRAE's guidelines are based on several factors like R/H, ambient temp., number of humans, etc.
And generally, temperature is not measured at a register but, velocity is. And a rather simple mathematical equation can tell you if the volume of air is adequate to heat or cool any given room.
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