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  1. #1
    Setting Up Camp
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    351M heating air flow

    I'm still trying to figure out my 351M's different systems. Concerning the HVAC, particularly the furnace and ducting, the air flow in the bedroom is very strong. For comparison, say, like a hair dryer on high. The air into the kitchen/living area not so much. It's very low.

    My first weekend in the RV the temps got down in the upper 20's. I set the temperature so that the heat would come on around 63 degrees and it did. But... by the time the living area reached the set point to turn the furnace off the bedroom was 76 degrees.

    I have been back and forth with the manufacturer via email. He indicated there was a false door that allows access to the furnace. I'll be darned if I can find it. I'm thinking I will have to go through wall in the underneath storage area.

    Can anyone advise me on how I can check this to see if I can fix this without going to the dealer? On the plus side, I don't think I will be needed the furnace for a while as temperatures are rising here.

    Thanks,
    Wayne
    2019 Grand Design Momentum 351M
    2018 Chevrolet Silverado 3500HD LTZ DRW CC 8 ft bed, B&W Companion hitch
    2018 Harley Davidson Roadglide Ultra
    2019 KTM 790 Adventure

  2. #2
    Setting Up Camp
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    I ended up removing a panel on the off street side of the underneath storage compartment which gave me a view of the ducting out of the furnace. Everything is attached. There are no crimps or pinches. The duct to the bedroom/bathroom is a straight shot across the rig. The rest of the duct work goes through a hole to the lower portion of the rig to heat the living area and garage. I can probably drop the spare tire to access that space.

    I spoke with a tech at Grand Design. He offered up that people were replacing the grating in the bedroom with a device that can baffle the air into the bedroom which may be a good option.
    2019 Grand Design Momentum 351M
    2018 Chevrolet Silverado 3500HD LTZ DRW CC 8 ft bed, B&W Companion hitch
    2018 Harley Davidson Roadglide Ultra
    2019 KTM 790 Adventure

  3. #3
    Left The Driveway IndianaFrog's Avatar
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    Did you do this and if so, did it increase the air pressure (flow) into the living area?

    This was my first thought as well, but didn't know if the ducting system is direct or on a trunk.

  4. #4
    Site Team xrated's Avatar
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    Based on what you've said so far, I still can't help but believe the is an "air leak" somewhere or more than just one place, which is allowing the heated air to escape from the ductwork before it gets to the outlet(s) that it is supposed to be going to. The only real way to know for sure is to visually look at the entire routing of every piece of ductwork and check all of it for leakage flow. The ventilation system operates on a positive pressure, produced by the furnace fan and if there is a leak or several leaks, that amount of air flow will be reduced at the end...or outlets.
    2016 F350 CrewCab Dually
    2018 Momentum 394M...Heavily Modded!
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    Excessive Payload is a Wonderful Thing

    "If it ain't fast....It ain't Fun"

  5. #5
    Big Traveler
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    Quote Originally Posted by NFurno View Post
    I'm still trying to figure out my 351M's different systems. Concerning the HVAC, particularly the furnace and ducting, the air flow in the bedroom is very strong. For comparison, say, like a hair dryer on high. The air into the kitchen/living area not so much. It's very low.

    My first weekend in the RV the temps got down in the upper 20's. I set the temperature so that the heat would come on around 63 degrees and it did. But... by the time the living area reached the set point to turn the furnace off the bedroom was 76 degrees.

    I have been back and forth with the manufacturer via email. He indicated there was a false door that allows access to the furnace. I'll be darned if I can find it. I'm thinking I will have to go through wall in the underneath storage area.

    Can anyone advise me on how I can check this to see if I can fix this without going to the dealer? On the plus side, I don't think I will be needed the furnace for a while as temperatures are rising here.

    Thanks,
    Wayne
    Every attachment nipple on my furnace leaked quite a bit of very hot air. Sealing the leaks with furnace tape was the first step. Removing the registers on the island revealed careless taping resulting in air blockage. This restored flow to the living area for me.

  6. #6
    Left The Driveway IndianaFrog's Avatar
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    I'll dig in a bit deeper this or next weekend. My first thoughts were a crimp in the hose or that airflow, like water will take the path of least resistance. What I didnt know for sure, if I put a vent cover that allows me to open/close the bedroom floor vent, will that help push more air through to other rooms? I "kind of did" when I test THAT, but wasnt sure if this would or could cause excess heat in the furnace.

    I'll start peaking around under the floor area.

    GD really needs to step up this kind of stuff. Why be like all the others..

    Sigh.

  7. #7
    Setting Up Camp Lawrencemountain's Avatar
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    I had the opposite with the heat. Good flow in the living room and none in the bedroom. Ialso had a super heated basement. Opened the basement service panels and found the duct disconnected from the bathroom/ bedroom. While there I routed wires and water lines to eliminate restrictions on the other ducts. Now I have good flow in all areas. All simple things that can be taken care of but also avoided.

  8. #8
    Setting Up Camp
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    I apologize for not following up on this post. I expected an email when someone responded but only received the one when Lawrencemoutain replied. I have not restricted the air flow to the bedroom to see if this increases the flow to the living and garage areas. I need to find the access panels and have a better look. I will block off the ducts in the bedroom and bathroom to see if air flow improves in the living area. I've scheduled time at the dealer in July for some improvements and repairs. I will request that they go over the ducting system and repair any leaks. I'm glad to hear that some have found a solution to this problem.

    Thank you for all the responses.
    2019 Grand Design Momentum 351M
    2018 Chevrolet Silverado 3500HD LTZ DRW CC 8 ft bed, B&W Companion hitch
    2018 Harley Davidson Roadglide Ultra
    2019 KTM 790 Adventure

  9. #9
    Setting Up Camp
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    The dealer found the that ducting to the living area and garage was crushed. I have verified a change in the area flow to the living area. The true test will be when the cold weather returns.
    2019 Grand Design Momentum 351M
    2018 Chevrolet Silverado 3500HD LTZ DRW CC 8 ft bed, B&W Companion hitch
    2018 Harley Davidson Roadglide Ultra
    2019 KTM 790 Adventure

  10. #10
    Seasoned Camper
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    I just found this post and wonder if you were able to test out the system this past winter?

    We bought our 351M this past year and over the Christmas holiday while staying in Roswell NM, we discovered our bedroom at 82 while living room was barely 65! It was below freezing several nights so my wife came up with a temporary fix. I worked out the details. I removed the 4" vent in the bedroom and installed a dryer vent coupler w/a one-way baffle (removed the baffle). Found a 6' flexible duct with a rubber slip seal and installed it over the coupler now installed in the wall. I fully stretched the duct and bent it back towards the living room. To our amazement, this kept the bedroom at 67ish while upping the felt heat in the living room. All with no vent into the bedroom. My guess is the dumping of heat down into the living room pushed the ceiling heat back into the cold bedroom. The end result works but we have to remember to step over it only once to get into the bathroom from the bedroom. All this done while in Roswell; a coupe of trips to the local box stores. For travel, just removed the duct and placed on the bed. I will look into the basement area to see if our duct is crushed for the living room.

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