Ventilation Systems Part 1 – Boats

The first in a multi-part series of articles on ventilation

Ventilation is one of the most complex aspects of any composting toilet system, but it shouldn’t be. Almost all urine diverting standard sized and compact composting toilets require ventilation. In some, like the Separatt, it is the sole means of removing the smell and moisture produced by processing the solid waste. Urine odor can be fairly well confined to it’s container, but pouring it out is a stinky process indeed, unless you have treated it with a holding tank solution. Treating it is common with mobile applications like boats and RVs because public restrooms are often the place they get emptied and you don’t want to chase everybody out of the bathroom and have them complaining to the management. But I digress . . . This is a series of articles on ventilation. First I will discuss boats, except for houseboats with RV type flush toilets that use a floor flange which I address in the Part 2 which is RV and travel trailers. Part 3 will be fixed applications like homesteads, cabins, tree houses, etc and Part 4 will be prepper bunkers which are a special case and Part 6 is tiny houses, also a special case.

When I first designed the C-Head, I had no doubt that I would have to ventilate the toilet. It is, after all, full of poop and pee so on the face of it, that was a no-brainer. Turns out, I was wrong. First let me point out that there are basically three methods that urine diverting toilets use to “compost” the waste. One is pure desiccation. This is done by forcing a relatively large amount of air over the waste, carrying away the odor and the moisture to the outside air. A 3-inch pipe and a continuously running electric fan are required. This is in effect what nature does when a dog takes a dump on the lawn. Nature also adds a good dose of heat and UV exposure via sunshine to the mix. This can work fairly well but it isn’t unheard of having the odor waft down from the vent stack to ground level on occasion and assault your senses. You may find yourself checking your shoe bottoms. Problems may also arrive if you have a power outage and if you are OTG it can draw a significant amount of your precious power. There are better ways.

The second method is mashing the waste into a carbon based medium and exposing and releasing the moisture contained therein, and then using a smaller fan system to continuously draw off the smell and moisture. Presumably, this accelerates the composting process or at least makes the waste look more like compost if nothing else. It certainly isn’t safe to handle the “compost” coming from this kind of toilet. One downside of this method is that ventilation is still required from an electric fan. In addition, the mashing process causes the waste to get packed into the corners of the collection container making emptying it more difficult, and these units tend to be larger than the next type (churning) making a difficult job even more difficult.

The third method is simply covering the waste. This can be done two ways: either by hand, sprinkling the medium over the waste or by using a churning device that creates a wave like action from the medium and rolls the waste thereby covering it evenly on all sides and continuing to cover it each time as the moisture moves to the surface. That is what the C-Head does. This method does not usually require any ventilation unless the toilet is installed in a confined space that is not ventilated itself, that is; no windows or hatches to move air. Ventilation may also be desirable if the toilet is being used in a humid climate as that prevents the moisture from escaping the toilet and creates the buildup of condensation. In this case the ventilation is used to remove the excess moisture. The waste doesn’t have a sewage smell but just a musty mild odor that isn’t especially unpleasant. But on most boats, lack of ambient ventilation is not usually the case. In our experience, hatches are usually open and air allowed to flow through below to keep things cool and prevent the buildup of mildew which as any live aboard boater will tell you is the plague.

So let me be honest. For most live aboard boat owners, or most boat owners in general for that matter, no ventilation of the C-Head is needed. At the very least, wait and see if you think you need it for condensation. Let me tell you my story. In building and installing my first C-Head, I cut a 3-inch hole in the balsa core deck of my almost new Gemini catamaran sailboat to install a solar mushroom fan for my ventilation system. I devised a plenum to sit below it that would capture any water that made it past the fan and direct it into the discharge limber hole of the sail locker. From there I snaked a flexible hose through the bulkhead into the head and attached it to my newly invented toilet. Voila! Fantastic ventilation system. It did have a few problems. Any sustained wind at anchor over 30 knots would over power the fan and push air back through the head into the cabin. We would get a musty smell that became immediately identifiable. I would go out on deck and install a cowl that when facing backward would immediately suck the musty smell out of the cabin. So, solved that problem.

I also would have to remember to remove the mushroom fan and cap the port shut if we were sailing to weather in large seas. Going forward to do this in rough seas was never fun. We never took a wave over the bow that put water into the vent system but it was always a possibility when the fan was in place. Fun and adventure, indeed!

Thing is, a year later, I removed the ventilation hose to do some modifications to the boat and lo and behold, a few days later, there was no smell. So I waited, and I waited and still no smell. Damn! All that aggravation and work for nothing . . . except creating more places for the boat to leak in the future. Today, I have 4 of my toilets in operation, one in my home, one in my office (the lab), one in one of my shop buildings and one in my RV. None of them are ventilated and none of them smell.

But you say, it is poop, it is pee, I want my toilet to be ventilated. Fair enough. The C-Head comes with a 12-foot section of 1.25 diameter flexible vent hose and the fittings necessary to run a vent line from inside the collection bucket itself to an outside port. It can be vented inside a dorade box, or a sail,utility or anchor locker, or on deck using a Nicro day/night solar vent, or you can install an inline fan and pretty much exit it anywhere. Each has its benefits and drawbacks. The dorade box will provide passive ventilation which will usually suffice and saves you electricity. You must be able to angle the cowl facing with its back to the wind. At anchor this is not an issue since you should be constantly swinging into the wind. At a dock though, you may have the wind coming at any angle.

Cowl for a dorade box

Venting the exhaust end into a locker is a good idea and usually the head isn’t far away from some kind of deck locker. The limber hole in the bottom of the locker is usually enough to circulate some air and remove any smell in a short time. This does require an inline fan. Inline fans have the advantage of being quiet since they can be free floating with the hose absorbing the vibrations or the brackets padded where the fan is installed. Mini fans are easy to replace and usually inexpensive. You can find them by googling “computer mini fan.” Note that the label on the fan gives you the voltage, amperage and decibels. Plans for inline installation are included in the owner’s manual and you can watch this video. (click here)

The Nicro day/night solar vent is very nice because it doesn’t require running wiring. I it is a little pricey ($150-$200) so shop around online. The battery can run down if you don’t get good sunlight for a couple of days which while not common isn’t that rare either. Since it is often mounted on a deck, it can produce a very faint hum using the deck as a sounding board. We could hear our fan on a very quiet night but it was installed within a few feet of our berth. The solar vent also requires a more sophisticated plumbing system since it is potentially exposed to boarding seas. All in all, I was very happy with our Nicro vent and have used it in other land based applications with good success.

So, you can ventilate your C-Head relatively easily. Every situation has unique problems and solutions. Some experimentation will be necessary and some changes made as time goes on. But again, I suggest you wait until you see how things work without ventilation.

Please feel free to make constructive comments or ask questions in the comments section below. Unless specifically stated, I am not endorsing any particular product or vendor. I do not receive any kind of compensation or free samples of the products that I do promote.

Copyright 2019 – C-Head LLC – All rights reserved on all content.

2 thoughts on “Ventilation Systems Part 1 – Boats”

  1. Sandy – I purchased your churnless shorty model a few years back and found it to be an excellent solution to the problems of the traditional MSD which I had removed. Following your advise I did not ventilate the original installation to see how that worked out. I left it for a couple of weeks in the poorly vented closed boat to test the limits. Sure enough I got condensation and some other disgusting bad effects. I cleaned it all up and designed my ventilation system based upon your model with computer fans. I ran my vent line to a location that vented outside of the boat and aft. I wanted to lure the flying menaces away from the source, and put a screen in the exit to block them from following the vent line back. Couldn’t be happier with the results. It’s not a fraction of the hassle of a pump out system, with far less maintenance. Instead of carrying around a tank full of sewage, I can now carry more potable water.
    I am getting ready to install your C-Head in a new acquisition, and think I would like to go with the churning model this time around. I believe it to be better suited to consuming the wet wipes and eliminating the need for a separate waste can, not to mention the horrified looks from instructing a new user what to do with the wipes. I found that properly installed and used, your C-Head is a compact, convenient, low maintenance, no smell alternative to the traditional MSD, and especially so for pocket cruisers.
    Looking forward to ordering my new one when the boat is ready.


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