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Old 10-23-2016, 07:16 AM   #1
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Not Getting Sufficient Heat From Furnace

Question for you more experienced DYI folks:

The furnace in our 25' 07 Safari is working but putting out insufficient heat.
The unit starts fine and provides heat, just seems not near as much heat as I recall last season.

Using my IR Thermometer, I measure exhaust temp at unit outside about 125 degrees, inside at the register closest to the furnace about 115 after the unit has been running a few minutes. Would anyone know what the normal temps should be at these locations?

We had the LP gas regulator replaced about two months ago, so I assume it is receiving sufficient gas.

Any thoughts appreciated.
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Old 10-23-2016, 09:26 AM   #2
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This is unlikely to be your problem, but could be something to check. On my '89 Excella, I had been working on the flexible furnace ducts last season. For some reason I did not hook the 2 flex hoses up that run to the bathroom and bedroom areas. I checked the furnace a couple of weeks ago before going to the installation rally for our unit. It was toasty under the sink area but chilly in the rest of the trailer!! A simple fix. Maybe you have a similar problem with the ductwork for your furnace.

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Old 10-23-2016, 09:34 AM   #3
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The output air temp would be somewhat dependent on it's temp going in, so could this be different than before? Do you think the fan is running at the same speed, is there a voltage drop (other stuff plugged in or on and drawing down the voltage, it doesn't take much with a 30 amp supply). Was the regulator set for the correct pressure when installed?
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Old 10-24-2016, 06:35 AM   #4
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Thanks for the responses so far.......

1. We are getting great airflow and the ducts all appear to be connected properly.
2. And outside air temps pretty consistent.
3. I do not own a gauge to measure the gas pressure, so need to check that. The tech that installed it seemed really competent, so I would be surprised if that is the issue....and he took a measurement after installation to make sure it was correct.

Still would be interested in what a normal exhaust temp might be and what temp you should read at the inside heat register closest to the furnace.

My best guess is perhaps the burner needs cleaning or servicing to ensure proper flame....but that is a guess at this point.
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Old 10-24-2016, 02:48 PM   #5
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Would you post your solution if/when you find one please? We have a similar problem. Furnace worked fine last winter. Air coming out of vents is hardly above room temp but the exhaust is HOT. Air flow seems normal.

Thanks for any help.
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Old 10-24-2016, 02:55 PM   #6
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Just my two $0.02, but that exhaust temp sounds way low. I have nothing to base this on, but is would expect closer to 200.
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Old 10-25-2016, 06:11 AM   #7
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Quote:
Originally Posted by sid42 View Post
Would you post your solution if/when you find one please? We have a similar problem. Furnace worked fine last winter. Air coming out of vents is hardly above room temp but the exhaust is HOT. Air flow seems normal.

Thanks for any help.
Sure will!
Thanks for responding.
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Old 10-25-2016, 06:28 AM   #8
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The air temp coming out of the supply side should be roughly 80-ish degrees F above the return intake air temp. Not sure what the AS design calls for. Thus the temps in Post #1 seem low. Can you remove one of the ducts at the furnace and measure the temp being discharged, vs. the interior temp of the trailer? Not sure if you have access to do this. If not, letting it run for a few minutes and measuring the discharge at the supply register is more or less the same, so taking the duct off is not that crucial.

Burner servicing/cleaning sounds like a good plan, as they can get really rusty especially if you travel in humid or foggy areas, in particular near salt water IMO, like Spanish Fort AL for instance!

Once disassembled, a new burner might be a good investment for a 10-year old trailer +/-. Other nearby parts would be candidates for new replacements also IMO, like the pilot light assembly or Piezo etc. sparker/igniter, depending on what you have.

Good luck!

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Old 10-25-2016, 10:47 AM   #9
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Quote:
Originally Posted by Alumitater View Post
Using my IR Thermometer, I measure exhaust temp at unit outside about 125 degrees, inside at the register closest to the furnace about 115 after the unit has been running a few minutes. Would anyone know what the normal temps should be at these locations?
Typically 140 at the register and a little higher at the exhaust.

Quote:
We had the LP gas regulator replaced about two months ago, so I assume it is receiving sufficient gas.
Only way to tell for sure is to measure the gas pressure while the furnace is running.

Be sure your propane bottles are reasonably full. It's easy to fool yourself if they don't have float gauges. Best thing to do if there is any doubt is remove them from the trailer and weigh them on a bathroom scale.
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Old 10-26-2016, 06:17 AM   #10
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Peter and Jammer:

Just the kind of information I was hoping for.
Thanks for passing along.

Sounds like a trip to the dealership is the best resolve....I undertake many repairs, but gas issues....now that's different!
I will post the results, my be a couple of weeks.

Thanks again to all who contributed.
Tom
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Old 10-26-2016, 08:05 AM   #11
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I checked my 2015 Classic, larger furnace, but getting 160-175 out of the primary vent by the door and 130-145 in the rear of the trailer. Exterior exhaust about 185.
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Old 10-26-2016, 09:49 AM   #12
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Dirt daubers in the the burner/exhaust tube?



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Old 10-26-2016, 11:36 AM   #13
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Thanks Alumitater, good luck at the dealer!

Peter
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Old 10-27-2016, 05:51 AM   #14
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Quote:
Originally Posted by ghaynes755 View Post
I checked my 2015 Classic, larger furnace, but getting 160-175 out of the primary vent by the door and 130-145 in the rear of the trailer. Exterior exhaust about 185.
Thanks! That sounds more like it.
We have Foley Airstream nearby in Gulfport....good folks.
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Old 10-27-2016, 06:41 AM   #15
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Definitely would recommend a inspection. One common issue I have seen is partial obstruction of the burner orifice. Usually by spider nests. The normal heat rise across the heat exchanger should be listed somewhere on the unit or literature. The two main factors are the temp of the flame and the airflow across the heat exchanger.
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Old 10-28-2016, 06:35 AM   #16
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Quote:
Originally Posted by h2ocoolerman View Post
Definitely would recommend a inspection. One common issue I have seen is partial obstruction of the burner orifice. Usually by spider nests. The normal heat rise across the heat exchanger should be listed somewhere on the unit or literature. The two main factors are the temp of the flame and the airflow across the heat exchanger.
Thanks, good guidance. I suspect a spider may be my issue. Just a gut feeling.
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Old 11-14-2016, 07:54 PM   #17
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update on issue

Thought I would report I took some time and my air compressor and gave the furnace cabinet and outlet areas a good blowing out. Then cranked up the furnace and after a few minutes was reading 140+ at register closest to furnace and 180+ at exhaust.

Cautiously optimistic that may have been spider web issue or some other obstruction. Will continue to test and monitor as our temps begin to drop here in LA (Lower Alabama).

Thanks for all your suggestions and information.
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