Hi, I’m confused about the best way to vent a simple humanure-style compost toilet located in a bathroom.  Is it better to place the fan as close to exit of vent pipe, so that it sucks rather than pushes the air?  It might be quieter, too, if it’s not in the toilet box.  Maybe the fan could be located outside, even?

Also, if there is a competing shower fan in the room, then how to prevent it from drawing air out from the toilet box (and stinking up the bathroom)?  I have read that the shower fan intake could, instead of being above the shower, just be the same vent pipe as the toilet box, drawing air through the toilet box.  In other words, the toilet box fan creates a relatively weak continual air flow, but when the shower fan is turned on then it just adds more power and so more air goes through the same pipe.  The advantage, apparently, is that there is no competition between fans, and humid air is drawn in at a low point, thereby keeping heat in the bathroom.

But, maybe this is just overkill?  Because, if the shower fan inlet is above the shower (as usual), then wouldn’t simply opening the window provide a source of incoming air, be enough to prevent sucking air from toilet box?

In Laura’s video about compost toilets, she for some reason seals with foam the top of the toilet.  Doesn’t that prevent air from coming in to the toilet box, to be vented?  Won’t it also cause condensation on the toilet seat (because of lack of air flow around the seat)?

Thank you for the help!

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Best Answer

Hi Eric,

For a true humanure style toilet you don’t need any ventilation. The sawdust or woodchip cover you add to the bucket seals off most odors, and since the bucket is filled rather quickly, there isn’t time for odors from decomposition to develop. Other styles of composting toilets that keep the material around for longer, or may have urine storage that has urine odor, will need a fan or vent.

I currently have a simple humanure sawdust bucket toilet, and we use woodchips to cover, no vent, no fans. No odor issues. The  standar bathroom fan doesn’t draw up odors. The issue with the bathroom fan you bring up is when there is a larger composting chamber below the toilet, that would be a source of more odors, which doesn’t happen with a 5 gallon bucket sawdust toilet.

A previous toilet I had, with urine diversion, had more odor from the urine tank so the seal on the toilet lid helped with that. I don’t find it necessary for a sawdust bucket toilet with no urine diversion.

If I were you, I’d set up your sawdust bucket toilet, experiment with cover materials, and see how it works without a fan. You could always add one in later on. (I would except you not to need any fan or vent.)

Hope this helps!



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I am a tiny house dweller now for 4 years and have designed my own composting toilet (dry bucket with sawdust and liquid diversion piped to outside storage and use for fertilizer) with a direct vent outside and have certainly thought through all of these things you’ve mentioned.  First, my toilet has evolved and become more air tight over the years with its next evolutionary phase towards becoming a vacuum.  The ducting is a short run outside with the fan housed between.  I do plan on ducting the 2″ pvc  further from my house (under ground to an outlet box(above ground)) and have considered a booster fan at this end.  Similarly, as my system has become more air tight the need for air intake is drastically important.  I am installing a one way “breather” valve or two (or three)notsureyet) to prevent the shower fan from over taking the toilet fan’s negative pressure.  I also have a single fan ERV that I switch to constant intake mode during showers to give the bathroom fan an intake source.  I have another prototype tiny house  build where I’m using a dual fan HRV ducted system and am experimenting with the exhaust portion of the design to be integrated with the toilet, but am certainly weary of this design because that duct consequently is tied into the kitchen and bedroom exhaust duct.  In a perfect world with proper baffle dampening to prevent backdraft it shouldn’t be a problem, but despite how well you labyrinth your exhaust port outside, high winds have a way of depressurizing even the headiest of forethought.  So, alas I hope to find my next gen toilet’s design, with a sealed vacuum system and air makeup one-way valve, and booster exhaust fan to be the ticket to counter the ebb and flow of pressure changes in the house when showering or opening the windows or simply running the ERV or HRV.  Yes, in a world of super tight envelopes around our modern abodes air flow, pressure and induction are complex topics, especially in small confined spaces.  Getting the temperature just right without compromising the quality of the air requires intention and attention to all the details.  ButT, hear this, never once has the rare instances of the compost bucket’s scent entering the house been worse than majority of my experiences with a traditional toilet room’s obscene stench after use.  Something about having a negative pressure under you while using the compost rig that transcends all things I thought I knew about the joys of number 2.  hey, Cheers,


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