Ventilation with Composting Toilet
Hello,
I am doing the builder/owner thing in mid-coast Maine, zone 6. Its a 1000 square foot well insulated and airtight box. I will stand walls interior of all the sealing and insulation/drywall to make a bathroom and bedroom. I am installing a composting toilet (Biolet 25a) in the bathroom which has a 2.5 inch vent stack through the roof.
The company recommends going without an extraction fan in the bathroom, lest poop smell be drawn out of the toilet. I have an email in to the town CEO about this, but at some point in the past, if i recall,…. if a 3 ft. square window was installed in a bathroom it was ok for code. no fan needed. I have a window that size. Has the code changed on this since then?
I am thinking of minimizing my penetrations and I will be using an erv/hrv and one heat pump per floor (2). I have a conditioned attic above the ceiling of the bathroom (where the erv/hrv will be)and I can run ducting and venting tube if need be, etc. Plenty of space and walls to mount intake and outtakes in to the main room, bedroom and bathroom. The range hood will be just on the other side of the wall, and can be incorporated into the venting strategy.
I would appreciate feedback on how to minimize penetrations and devise a ventilation plan that would work. The goal is to limit poop smell while venting vapor and creating good air flow in all rooms. I am considering small wall fans in the bedroom and bathroom to move heat in, or leaving the top of the open stud interior wall framing open for air flow. I live alone and privacy is not a concern.
Thanks in advance.
Stephen
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Replies
It's not crystal clear in the code, at least not in the 2015 IRC that Maine uses. In chapter 3, it requires an operable window, but allows for no window if mechanical ventilation is used. https://codes.iccsafe.org/content/IRC2015/chapter-3-building-planning#IRC2015_Pt03_Ch03_SecR303.3
Chapter 15 lays out the requirements if you are using mechanical ventilation: https://codes.iccsafe.org/content/IRC2015/chapter-15-exhaust-systems#IRC2015_Pt05_Ch15_SecM1507.4
But Maine's code also references ASHRAE 62.2, which requires mechanical ventilation in bathrooms.
You could ask your local code official for their interpretation. I always use mechanical ventilation in bathrooms, even in the on I just built for my off-grid mother-in-law, but I understand why mechanical ventilation would not match well with a passively vented waterless toilet.
Stephen,
I wonder if you could provide exhaust ventilation and deal with odors by providing a fan that pressurized the space, and passive exhaust vents - or even just rely on the toilet vent? To be effective, that would necessitate keeping the room enclosed.
Those toilets vent from the composting area up through the roof vent. The one I had also had an inbox heater in case the compost didn't warm up enough. This also triggered an in toilet fan for the vent.
If operated properly, they don't really smell. If you try to mechanically draw the smell out of the toilet, into the bathroom air and then out a window or bathroom fan, then it will almost certainly smell as you pull it into the room instead of letting it go up the stack.
If your toilet doesn't have an in vent fan, that would be my choice. As it is, you're going to have a 2.5 inch vent stack uncontrollably venting heat (and smell) out of your house, like a fireplace chimney that's always open. I don't see any other solution. other than a real toilet or an outhouse. These things need to be vented from the back of the unit.
Thanks very much for the code references, Michael. I will circle back when I hear from the code officer.
The compost toilet does have a stack through the roof, two heating elements and a fan. There shouldn't be a problem with it venting, the only potential problem is backdraft, when a vent or window is open in the bathroom. Seeing how the compost toilet has a fan, however, I think the backdraft would be minimum and only on the occasions that the extractor fan is on.
Malcolm et al., do you think that creating a tight bathroom is important in this situation? And does this tightness mean that no heat-moving wall fans or erv/hrv vent covers should be installed in the bathroom? Essentially, then, it would just be the toilet, an extraction fan (assuming this is code necessary) and an interior door that seals pretty well.
It should
stephenr,
No. I think having the bathroom tight would only matter if you were cooking up a Heath-Robinson system like the one I was musing about. A bit of positive pressure would be helpful if your ventilation system could provide it though.