Composting vent - fan speed timer and exit options

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warx

Active member
I was thinking it would be cool to have our composting toilet vent fan have two speeds - normal and high. Would be great if you could hit a button (or trigger it from lifting the cover) to run high for 20 mins then return to normal speed. I have not seen anything like this even though these PWM controllers get pretty fancy for computer cooling systems.

Also looking to vent through the floor but recall there are some concerns with back pressure if you don't do this correctly. Again struggling to re-find what others have done to circumvent (ahem) this problem.

One more thing; I want to make this bench toilet removable so hoping the vent system can be disconnected and thus trying to keep the vent diameter to a minimum. I wonder given the fan would be operating on two speeds and I don't mind some noise when on high I could use 1" OD PVC pipe.
 
Outlookela

Outlookela

Active member
I have a airhead model installed. Haven’t seen the need for a higher speed fan.
Unit it is quite removable but I have never wanted to. About a ten minute job. Maybe if I was camped somewhere for a long time. Vent is through floor. Some situations where I have a combination of roof vents and windows open while driving have gotten a whiff. Haven’t really figured it out but haven’t felt the need to due to its rarity and mildness. Didn’t want a roof or side exhaust. I think floor is the practical way to go. I am a weekend warrior/2 week tripper. Could be different for a full time couple.
 
65C02

65C02

404
I've seen similar 'turn off the fan' questions come up in the marine forums. The vent fan must be left on continuously. Its job is desiccation - to remove the moisture in the coir - things get real ugly in the compost heap if you don't get rid of the moisture - a moldy stinky mess. I would imagine if the S pail is completely dried out, you could get away with the fan being turned off. Running on High then to Normal would mean you are running the fan over voltage - which it may not appreciate. We have an AirHead (WE LOVE IT)- running two hoses thru the van floor. One as an intake the other exhaust - that avoids setting up a reverse air flow due to negative air pressure when I run my two Maxx roof fans. If you have an AirHead - call them, they have excellent support. If you don't have your toilet yet - good luck, I just noticed they have a 5+ week lead time due to covid.
 
Outlookela

Outlookela

Active member
I keep a roof vent cracked all the time. I think the continuous fan it helps dehumidify the van over the pacific nw winter
Van heats up during day draws in low humidity air exhausts high humidity air. Would think it adds up to gallons over the winter.
 
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warx

Active member
The intent was not to turn it off (except when the toilet is not in use) or run over power, high = 100% PWM of like a 46CFM 80mm fan low would be like 60% for regular desiccation.The high mode really would just be for "during the event" to keep it more self contained. If a 2W (0.2A) typical 80mm fan does fine "during" and for 24/7 with no speed change I'll just go with that.

I like the two hose idea for pressure balancing. What size hoses are we talking about? Most vents I see are 2" which is a substantial hole to cut twice. Besides having an exit with an insect screen is there any fancy under floor louvre system that works best (not trying to keep vertical rain out so maybe just the screen is enough).

I bought a diverter from Strump & Trollup in the UK so am making my own box (2.5 gallon bucket, 1 gallon bottle). It comes with a nice rear hole cover which might work or not for the modest.
 
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Svetlonio

Member
I have installed a Nature's Head composting toilet on my van, so maybe I can help!

I don't know if this is common to all Sprinters, but on mine, below the floor level, there are factory holes (covered by plastic caps) that allow access to the space between inner and outer walls (see picture). This is where I routed my vent (I used 1 1/4 inch PVC simply because that's the size of the vent cap that came with the toilet); it means that the hole in the floor is behind the wall, easy to hide, and didn't require cutting a hole through the actual (wooden) floor.

It also means that my vent has multiple 90 degree bends in it, so I was worried that the tiny fan that comes with the Nature's Head would not be powerful enough to force air downwards through it. So I am using a ridiculously oversized 150W bilge blower (and a PWM controller). I could not find anything smaller that runs on 12V and can be installed inline - I am interested in alternatives!

I have the fan running at the lowest speed the dimmer will allow, which draws about 3W, and after about 2 months of use I have never needed to increase it. In fact I now suspect that the stock computer-style fan that came with toilet might have been enough (but I haven't spent the time rewiring to confirm it). If you are venting straight down I don't think you'll need much power at all.
 

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sprint2freedom

2008 NCV3 170ext
I live with an Air Head as my primary toilet, and I don't see a point to a two speed system. I don't smell the "event" unless I place my face directly over the opening and deeply inhale (or if I'm using a flush toilet- that's right, the composting toilet is superior).

Air Head uses a 1.5" ID hose. You might get away with 1" but a higher flow (and higher noise) fan may be necessary, or perhaps you can keep the hose very short and avoid bends to minimize air flow resistance.

Be advised that cleaning the in-line vent screen is a regular required maintenance item. It's easy to forget about this one, but dust will gradually block the screen and impede ventilation.

Airflow balance is worth worrying about, and is straightforward to do with an Air Head. The whole unit is sealed. If following the owner's manual, you would install the hose on the left or right hand side according to your preference. The other side gets a tiny snap-in inlet screen. Air is drawn through that screen from the interior of your van, over the solids tank, and through the fan to outside. With a roof fan set on high this airflow can reverse direction and result in a sour odor. So, purchase an additional length of hose (or use what you have left over) and an additional fan flange, but no 2nd fan. Connect a hose to both sides of the toilet, and plumb both hoses to outside. Now you just have to remember not to have the roof fan on exhaust while the lid is up.
 
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warx

Active member
OK, so I did a quick experiment. I printed a reducer for a 80x80mm fan down to 1-1/2" PVC size. I bought two fans - the 80x80 @ 0.20A 43CFM 31dB and a blower (centrifugal) fan smaller and a smaller exit of 20x30mm rated at 0.15A and 9.4CFM 28.5dB . The axial fan pushes a lot of air when not restricted. As soon as you put the reducer on there the air flow drops dramatically. The centrifugal fan does not - through the 1-1/2" PVC it has more flow. Also it's quieter and possibly easier to mount. I think since it is able to run at higher dynamic pressure I can use 1-1/4 or even 1" PVC - but I did order some of the Natures Head flexible hose which I think is 1-1/2" OD. I guess building those hovercraft taught me something after all.

These are the two fans:

Amazon.com: Gdstime 80mm x 25mm 8025B 12V Dual Ball Bearing DC Brushless Cooling Fan: Computers & Accessories

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Amazon.com: 75mm x 30mm 7530 12V Dual Ball Bearing DC Brushless Cooling Blower Fan, AV-F7530MB: Computers & Accessories

Buy 75mm x 30mm 7530 12V Dual Ball Bearing DC Brushless Cooling Blower Fan, AV-F7530MB: Case Fans - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
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