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Old 01-31-2018, 11:01 AM   #21
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Originally Posted by Trobec View Post
On my 2015 f285 I don't think that grate is for cold air return like a house furnace. On the outside where the furnace exhaust is there is another tube just above the exhaust tube that draws fresh air into the furnace. I believe the grate is just a cover to access the furnace. I could be wrong but I have had my furnace out to replace the board and that how it appeared to function to me.
You're incorrect. That 2nd outside tube is the intake for your combustion air. The other is the exhaust for the combustion air. They do NOT ever come in contact with the air inside your rig. The combustion side never touches the warm air side. If it did, you'd be dead from CO poisoning.

If you have a high efficiency hot air furnace at home, you'll see it works exactly the same. You'll have two PVC pipes coming out of the side of the house for combustion air, but your house will have supply and return registers in each room.

There are many versions of RV furnaces, but All RV furnaces have some kind of cold air return grate or slots. You can see the one in my Roo under the dinette bench (it looks like a door, but there's a grating on it).
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You can see there's another grate that makes up the entire end of the furnace that's pointing at you in the pic. My Mini Lite has one just like it, but I don't have a pic.

Look at the pics in the attached manual (especially Fig 1 on page 5) and you'll clearly see slots in the sides of the furnace for the cold air that comes back through the grating to get back into the furnace.

Here's a better pic of one model:


Here's a pic of one more like mine:
Attached Files
File Type: pdf Suburban Furnace Service Manual.pdf (4.92 MB, 8 views)
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Old 01-31-2018, 11:16 AM   #22
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Old 01-31-2018, 10:37 PM   #23
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rockfordroo, I will attach 3 new pics. One from the front and one on each side... one of the side pics is not very good but if you zoom you can see it pretty well. I question how much "intake" air flow there can be from the front of the unit when its all solid, no vents, across the front and down each side til it gets to the back outside wall. UPDATE: I've ran two tanks of propane through it now and have had it run steady for 1-2 hours at 80 degrees setting on the thermostat without shutting off. I've bumped the temp down and bumped it up and it shuts off and on perfectly fine. Will keep testing it, but I don't believe there's going to be a problem with using those two front knock outs. Two things I'd recommend to anyone considering it: you might only need to knock out one of the plugs. Having both knocked out blows a lot of heat.... but there still is good airflow in the bedroom and garage. And, second, make sure to use the 4" extension pipe in the knock out to capture the heat and direct it out, right up against the vent cover and into the camper.
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Old 01-31-2018, 11:22 PM   #24
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I'm not telling you that the ONLY return air is coming in through the vent, but it is the largest and lowest resistance path, therefore MOST of your return air is coming in there. Unless you have large holes in your cabinetry, any other air is leaking in through cracks and crevices around drawer, doors and floors.

In your original pics, there is clearly a large area for air flow from the vent, around the hot air ducts on each side, and back to the intake slots on the furnace.

But I'm glad it's working for you.

In your new pics, it looks like there are 2 hot air vent ducts on each side of the furnace. I'm assuming you've checked ALL 4 of them for collapsed ducting or other blockages? One of them appears to be only a 2" duct. Where does that one run to?
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Old 01-31-2018, 11:58 PM   #25
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Originally Posted by rockfordroo View Post
I'm not telling you that the ONLY return air is coming in through the vent, but it is the largest and lowest resistance path, therefore MOST of your return air is coming in there. Unless you have large holes in your cabinetry, any other air is leaking in through cracks and crevices around drawer, doors and floors.

In your original pics, there is clearly a large area for air flow from the vent, around the hot air ducts on each side, and back to the intake slots on the furnace.

But I'm glad it's working for you.

In your new pics, it looks like there are 2 hot air vent ducts on each side of the furnace. I'm assuming you've checked ALL 4 of them for collapsed ducting or other blockages? One of them appears to be only a 2" duct. Where does that one run to?
The 2" duct goes straight down and under the floor. The heater pipes are all fine, not crushed. The heat blows good out all the vents but the bathroom (I have that one plugged right now until I can fix it). And the kitchen cabinet enclosure under the counter top has openings from one section to the other - looks like a large area to pull air into the furnace if it wasn't getting enough from that front vent where the knockouts are located.
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Old 02-04-2018, 08:13 PM   #26
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So here's my new addition.....the vent spins inside of itself so I can direct it or close it completely.
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Old 02-04-2018, 09:39 PM   #27
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Turned out pretty nice. If you need more heat I wouldn't hesitate to punch out the other one too.... mine has been working fine with both knocked out. You'll find the left side blows a little more air because the burners inside are more open. My next mod on the furnace is replacing a 4" duct to a 2" duct going to the bathroom. Just ordered the parts today off Amazon.
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Old 02-04-2018, 10:32 PM   #28
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Just wanted to add that the outside fresh air tube does connect directly to the blower motor.
Yes, there is an exhaust and an intake. The intake and exhaust is for the combustion chamber which is isolated from the rest of the unit. No air/no combustion.
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Old 02-04-2018, 10:48 PM   #29
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Yeah,I got that. For some reason I thought hooked to the fan. I know the fundamentals of fire and how it works.
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Old 02-04-2018, 11:05 PM   #30
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Quote:
Originally Posted by Trobec View Post
Just wanted to add that the outside fresh air tube does connect directly to the blower motor.
Quote:
Originally Posted by bubbles View Post
Yes, there is an exhaust and an intake. The intake and exhaust is for the combustion chamber which is isolated from the rest of the unit. No air/no combustion.
Just to elaborate and hopefully correct any preconceptions:

The blower motor actually has fan on each end. You can see them in this video:



I've also attached a parts document. On page 5 you can see the Room Air Wheel, which is on the left end of the motor in the video and the Combustion Air Wheel on the right side of the motor in the video.

The combustion air comes in the bottom tube on the right side in the video and the exhaust air goes out the upper tube on the right side in the video. Here's the intake/exhaust on the side of your TT; you can see how it matches the tubes in the video:

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None of this combustion air/exhaust air ever touches the room air. There is a heat exchanger wall between them. If this wall cracks, though, you will get carbon monoxide into your room air - a very bad situation. This is why you (should) have a CO/LP monitor in your rig.
Attached Files
File Type: pdf Suburban RV Appliances Parts Manual.pdf (339.2 KB, 14 views)
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2012 Roo19 - hybrid (2012-2015)

2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado 1500 Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10
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