Forum Discussion

Marsland's avatar
Marsland
Explorer
May 12, 2013

Flexible Heater Ducting

I have never liked the flexible heater duct material. I know it's the cheapest and quickest way to install ducting but it is also very inefficient. The flow coefficient is just lousy and if it could be replaced with something 'smoother' you would use a lot less gas and have much greater air flow. I understand (sort of) the reason it's used but has anyone retrofitted their RV with rigid or semi rigid duct work? Granted, getting to the existing ducts may be problematic, but I have had units that the ducts were accessible. Replacing at least what a person could get to would be beneficial I would think.

Am I out in left field with this or just being anal?

Richard
  • phays's avatar
    phays
    Explorer
    May 13, 2013
    If you can get at the connections check to make sure they aren't leaking. Flex duct is almost too simple to install and many times the installer doesn't take the time to make sure there is a good air seal. The air seal is done with good tape or mastic while the mechanical part of the connection is done with a hose clamp.
  • doughere's avatar
    doughere
    Explorer
    May 13, 2013
    I doubt that you will get much more heat with smooth duct. If you get more flow, it will just be a bit cooler.

    The best test to see if the ductwork is sufficient; is to check the difference between the inlet and discharge temperature. The installation manual will give a maximum pickup for your furnace.

    Regards,
    Doug
  • skipnchar's avatar
    skipnchar
    Explorer
    May 13, 2013
    Depending on your particular RV model, make and style, it may not be that difficult to make the change. If your RV has an enclosed belly you would need to remove the belly pan (Corroplex) and it should be easily accessible.
  • past-MIdirector's avatar
    past-MIdirector
    Explorer
    May 13, 2013
    If you can get access then the rigid duct would be better. Just like on the home dryer the air flow and heat is more productive with the rigid Aluminum pipe that comes in Elbows and 3' sections that are taped together with Aluminum tape and not duct tape. Stay away from the semi rigid that comes in usually 10' sections because it's to thin and crushes to easy.
    The flexable pipe they run is good if it's stretched out but most of the time it's just balled up with way to may turns.
  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    May 12, 2013
    RV furnaces do not start out with the most robust fans but I doubt that changing the duct work to a rigid smooth type is going to "improve" the air flow.

    Part of the issue is the limited amount of heat from the burner. The fan is chosen to give a compromise of air flow vs temperature rise.

    If you moved more air the temp rise will be to low and all you feel is a very cold draft.

    Move not enough air and you get to much temp rise and then risk overheating the furnace.

    The higher BTU the furnace the more air the fan will move, the drawback there is the more air moved by the fan the higher the 12V current draw of the fan.
  • downtheroad's avatar
    downtheroad
    Explorer
    May 12, 2013
    Not in left field at all. Our present rig has rigid (sheet metal) duct work throughout. Air flow is noticeably better than our previous trailer (which was very weak)...this has to be at least one of the reasons why.

    But, retro-fitting seems like it would be very difficult without ripping up lots of stuff.
    Anyway, good luck with it.

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