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Old 12-21-2018, 10:06 AM   #1
Matrap27
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Another question about furnace fresh air return

We have a 2011 Montana 3150. We don't camp much in the winter until this year. I have read on here where the vent under the stairs need to be left open for the return air for the furnace, but what about the vent under the fridge it draws air when the furnace is running also. I was wondering if this one could be blocked off as that is where alot of the noise comes, or at least put a good pleated filter in there?
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Old 12-21-2018, 11:16 AM   #2
waynemoore
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If you have ever removed the wall in the basement you will see that there is plenty of makeup air there. I have closed the vents under the stairs on every rig I have owned. I know I will be bombarded with people who have a different perspective. And yes I know that many will say that it may take a bit more propane to heat the colder air from that area by not pulling it from the living area of the rig. Again look where the furnace is and see all the open area there is. Or try holding a pice of paper over that intake and see if the furnace is drawing all that much air? Just my 2 cents on this topic.
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Old 12-21-2018, 11:36 AM   #3
carl n susan
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I believe in your model the furnace is under the refer and that vent there is the cold air return. You should be able to block off the area under the steps with no consequence.
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Old 12-21-2018, 01:08 PM   #4
Mudchief
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Wayne, you right as long as no generator is running. I had mine blocked and when the furnace was running it sucked the fumes in from the generator.
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Old 12-21-2018, 03:47 PM   #5
waynemoore
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A very good point. And just when I thought I knew everting.
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Old 12-22-2018, 07:51 AM   #6
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Originally Posted by carl n susan View Post
I believe in your model the furnace is under the refer and that vent there is the cold air return. You should be able to block off the area under the steps with no consequence.
True, and the furnace was much more efficient under the refer. Didn't do a very good job at keeping holding tanks from freezing though. Living in the south don't worry too much about freezing holding tanks. Wish my furnace was under refer. Don't like mixing cabin air with storage compartment air.
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Old 01-06-2019, 08:21 PM   #7
Bad Moon
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Originally Posted by waynemoore View Post
If you have ever removed the wall in the basement you will see that there is plenty of makeup air there. I have closed the vents under the stairs on every rig I have owned. I know I will be bombarded with people who have a different perspective. And yes I know that many will say that it may take a bit more propane to heat the colder air from that area by not pulling it from the living area of the rig. Again look where the furnace is and see all the open area there is. Or try holding a pice of paper over that intake and see if the furnace is drawing all that much air? Just my 2 cents on this topic.
One issue with that is when the furnace first starts up and just before it shuts down, the fan is blowing without the burner fired-up, therefore you are sucking cold air from the basement and blowing it into your trailer. I am looking at backdraft dampers to put on my return air vents. If I ever get around to doing it, I will post photos on here. I hate those drafts under the stairs. Too bad the basements are t better sealed and insulated.
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Old 01-06-2019, 09:50 PM   #8
DQDick
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Several of us have sealed and insulated the basements. There are a number of ways it's been done out there.
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Old 01-08-2019, 10:13 PM   #9
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The return grates under the stairs aren’t ducted to the furnace in any way manner or form. They are only there to let air out of the trailer when the furnace is running. Otherwise the furnace would pressurize the cabin and the furnace would stop moving air.

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Old 01-09-2019, 10:55 AM   #10
richfaa
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We are in moderate climates year round and the furnace gets light use. We use the A/C way more than the furnace. The fireplace in our prime source of heat here in Florida. There are many sources of intake air in these things as they are full of holes. We block off our step vents.
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Old 01-09-2019, 11:31 AM   #11
Soon 2B snowbird
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where would the cold air return for the furnace be on a 3791RD if not from the stair vents? I do not see any other return vents and the refrigerator is a long way from the furnace on this model?
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Old 01-09-2019, 10:57 PM   #12
MARK A
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Originally Posted by Soon 2B snowbird View Post
where would the cold air return for the furnace be on a 3791RD if not from the stair vents? I do not see any other return vents and the refrigerator is a long way from the furnace on this model?

The 3791 I looked at on RV trader had a return grille on the face of the second step going up to the bedroom.


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Old 01-10-2019, 03:56 PM   #13
prndl
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Maybe I'm missing something but if the furnace is in the basement and it gets the makeup air from that area to heat and then blow into the living area, why would I not want it to get some return/pre warmed air to recycle and heat rather than a continuous supply of cold outside air?
The stair vents provide that return air for the heater.
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Old 01-11-2019, 05:08 PM   #14
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Originally Posted by MARK A View Post
The return grates under the stairs aren’t ducted to the furnace in any way manner or form. They are only there to let air out of the trailer when the furnace is running. Otherwise the furnace would pressurize the cabin and the furnace would stop moving air.

Mark
Although there is no “duct” for return air, the basement itself acts as a return air plenum.
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Old 01-11-2019, 05:42 PM   #15
MARK A
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Although there is no “duct” for return air, the basement itself acts as a return air plenum.
You are correct, however the only air that goes through those returns is pushed through by the hot air coming in. The furnace is getting most if not all it’s returning air from the under belly of the trailer.

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