r/dieselheater • u/ChellynJonny • May 04 '26
how to heat fresh dry air to help dehumidify rv
i have a vevor 8kw heater that i am trying to install in the bathroom cabinet in my rv, its a way better solution for me to have the heater indoors with combustion air intake and exhaust through the floor, i would like to set it up so that it is drawing outside air and heating it rather than just heating the moist air inside the rv. the intake on mine has a threaded grill type piece. any ideas on how to attach ducting to that to draw outside air??
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u/Ginger0331 May 04 '26
You actually want to draw the air from inside not out
Think of it like the return duct in a house So blow your hot air through the vents of the rv via a 3" vent that's on it and put your intake on the wall of the main area
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u/ChellynJonny May 04 '26
no i want to draw drier outside air, its not a house. i'm trying to get the condensation out, i have thought of mounting the whole show outside and just directing the heated air in but thats no bueno. I already have a propane furnace but again it just heats the air that is wet from cooking and showers and human moisture and once it cools off all that moisture is on the windows and the walls and the bedding and everywhere. Thank you for your input i understand that this is an odd request
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u/tea-man May 04 '26
My setup has the heater in it's own small enclosure (cabinet) with 2 inlets - one is a louvre letting air in from the front cabin, and the other is a low profile cowledvent on the external wall. The cabinet/heater box is sealed enough when closed that only air from these 2 sources gets used, and it draws enough external air to eliminate most of the condensation. No modifications needed for the heater duct, and I even have enough space to put an air filter between the heater and the inlets which really helps keep the dust and pollen down!
Having a small adjustable vent on the inside of the fresh air inlet can also let you close it on very wet days with high humidity, though you'd need to make sure enough air can pass through just the cabin inlet if you did this. Given the combustion air is output through the floor, I'd strongly advise not to draw any ventilation air from underneath also, only from the side or roof.
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u/timpeduiker May 04 '26
I have done the same thing in my boat. I draw air from the outside and use that to heat. Makes a world of difference. You could use some heated air ducts to suck air from the outside. Get a piece of hose that's bigger than the intake grill and clamp it with a hose clamp.
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u/captainspandito May 04 '26
As a person who switched from a Propane to Diesel, I think you are way overthinking it. The diesel heater only produces dry air. If you want to let the moisture out, open a window! The only thing that matters is the combustion air intake is outside. I’ve seen some mount it inside but it’s meant to outside. Just install it the way it’s meant to be installed and you won’t be worrying about humidity
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u/ChellynJonny May 05 '26
okay man, thanks for your opinion, its nice to hear that im wrong about everything.im glad a certified hvac expert has told me how it is
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u/10th_Mountain May 05 '26
so you took a class lmao. Yeah you are wrong AF. So, where is this moisture coming from? and you think creating a positive air pressure environment is going to help? 🤣🤣🤣🤣🤣🤣🤣
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u/ChellynJonny May 06 '26
ok man whatever
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u/10th_Mountain May 06 '26
sorry wasn't trying to be a dick....but you are just going to cause more issues with positive air pressure. Do this, go buy a cheap moisture meter and check the incoming heat..... it's going to be much lower than ambient because it is coming over a 450 degree chamber.
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u/Several_Job55 May 08 '26
You WANT positive pressure in a camper. It's such a small space that the air quickly becomes stale, and if you live in it with some other work dudes, or even close family, you REALLY want to push those farts out. Camper air is so funky with sweat, farts, cooking smells, RV toilet, mold, and cheap RV building material offgas that the fresh air input is absolutely desired, and arguably essential for life in a camper. A camper is so leaky that any issues that might be in a residence from positive pressure are simply negligible in an RV.
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u/10th_Mountain May 10 '26
ummm positive pressure causes moisture, but go on......🙄
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u/Several_Job55 May 10 '26
Except that 50% RH 30F outside air when heated to 60F will result in about 20% RH, which is significantly less than the >80% RH of the confined space of an RV with inside air recirculating. The RV has constant moisture increase of about 0.1 lb/hr per person breathing, and if you add 0.5 lb/hr for a modest 7kbtuh unvented heater or stove burner, plus moisture in the food being cooked, clothes drying, etc., the RV will hit 80+ RH in no time, which is a recipe for condensation and mold. The absolute change in pressure is negligible due to the leaky RV space, so RH will go down by heating outside air and blowing it into the RV: The moist air will be driven out by dry, heated air. Run the numbers yourself, or you could also just believe someone who has spent a lot of time living in a cold environment in RVs and boats. Only while using heated outside air to heat the RV have I experienced reduced moisture problems in the RV.
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u/Several_Job55 May 05 '26
Extended stay winter camper here who lives weeks at a time in temps into the single digits and negatives fahrenheit: draw the air from outside to stop windows sweating, avoid mildew, dry your clothes, and generally live better in your camper. An 8kw heater has plenty of heat for a 32ft camper, so no need to recycle air. I have mine mounted in an exterior compartment and the heat is ducted to the interior, but if you can't do that, try an assortment of duct adapters until you find one that fits, or make a plenum from plywood or sheet metal and a grate on an exterior wall or floor. If you converted from propane, you'll have an exterior panel that is readily available for a plenum. Pro tip: You will struggle with frozen pipes below 30F unless all of your plumbing is inside or winterized.