Furnace running very hot...

[groundhogy]

So I have been noticing that my vent air has been notceably hotter.
Like too hot.
So I went to the furnace and put my hand on it. It is also too hot.

It is not triggering the over temperature sensor.

It is a 1 year old Attwood/Dometic 30k btu. The new model they are selling.

What types of things can cause this?

The air is blowing just as fast as ever.

[groundhogy]

... umm
I thought that if I pointed out some interesting observation about the high exhaust temperature, no one would notice what a dummy I was getting a case of the vapors over a perfectly normal furnace.

[larry_cad]

groundhogy wrote:
You can melt solder with that exhaust temperature

The inner core of the propane candle flame is
light blue, with a temerature of around 1500 C which is 2732 F.
You can almost melt steel with that. What is your point?

[groundhogy]

You can melt solder with that exhaust temperature

[DrewE]

groundhogy wrote:
I just pulled up the pdf installation guide and read this...

Adjust ducting installation to obtain an air temperature rise of 100°F-130°F. Also see air flow check section.

Sounds like you're right on spec, then, with a bit over a 110 degree temperature rise (68 to 180 degrees).

[groundhogy]

I just pulled up the pdf installation guide and read this...

Adjust ducting installation to obtain an air temperature rise of 100°F-130°F. Also see air flow check section.

[groundhogy]

Those are after steady state was reached.

The furnace is a 30k BTU

[groundhogy]

Initial Air temp: 68.5 F
Enclosure temp: 180 F
Duct temp: 165 F
Exhaust temp: 518 F
Final air temp: 82 F

[groundhogy]

I doubt the fire box is cracked.
This furnace is pretty new. Stuff still looks pretty shiny.


Atwood Model AFMD30111

[groundhogy]

A common rule of thumb is that 50 degrees C is the point where a person can barely keep their hand on something.
I could not keep my hand on the furnace enclosure.

I have a fluke multi meter with temperature probe.
If you have specific temperature spots you want measured, let me know.
Guess I will do the enclosure temperature and duct air temp?

I will also see if i can find info on the label.

[Sam_Spade]

DrewE wrote:
A "normal" thermometer is the right tool to measure air temperature.

While that is essentially true, if the air is flowing out of a metal grate, measuring the temp of the "fins" on the grate gives a good approximation.
If the grate is not metal, the reading won't be as good.....but still not useless.

[dougrainer]

He stated that he cannot keep his hand on the Furnace casing. THAT IS NORMAL. Doug

[DrewE]

Bobbo wrote:
I agree with needing an actual temperature measurement.

IR Thermometer

Very handy gizmos, but not good for measuring air temperatures; they measure surface temperatures based on infrared radiation from the surface. A "normal" thermometer is the right tool to measure air temperature.

[Bobbo]

I agree with needing an actual temperature measurement.

IR Thermometer

[Sam_Spade]

groundhogy wrote:
“you are getting HOT flue gasses into the inside loop.”

Please explain further

A gas furnace has a "heat exchanger", which is a metal box with two pathways for air flow. One path handles the hot flue gasses and the metal structure transfers the heat to the other path which circulates the inside air.

The air flow in those two loops should NOT mix with each other. If there is a "hole" inside the heat exchanger, you can get the flue gasses inside and that might make the inside air much hotter than normal. That condition would also be dangers because of carbon monoxide.

It is impossible for anybody to gauge "too hot" without being there. IF....yours is designed so that the fan does not come on until AFTER the flame has been on for a while, then the initial blast of air when the fan does start can be quite hot.....and will cool down a bit as it runs.

And I don't know exactly what part you are trying to touch and finding it "too hot"......but that likely is normal for most of the internal parts, except for the incoming gas pipes and the very outside case.