Room Ventilation and Extraction Systems Guide

All composting toilets have ventilation systems to aid composting and make toilet use odour-free. These ventilation systems can be electric or passive. They exhaust air from the composting chamber and are a necessary part of air-flow dynamics and code requirements.

It is important to correctly size and spec your composting toilet ventilation system in relation to your other household ventilation systems. Household ventilation systems should not override composting toilet ventilation with counter-flow of air from extractor units, home ventilation systems, or heavy natural drafts.

Standard Bathroom / Toilet Room Ventilation Types

In accordance with the building code, it is standard practice to use one of the following for ventilation of bathrooms and toilet rooms:

• Electric extractor units, often through-the-wall or inline
• Passive ducted wind-driven ventilation, such as turbo vents or convection-current systems
• Passive ventilation through a window or skylight
• Home ventilation and central heating systems

Below is a breakdown of these systems and advice on running them without compromising composting toilet ventilation.

Electric Extractor

Standard extractor systems are designed to suck air out of a room and blow it outside where it is dispersed. This is counter-intuitive when used in conjunction with a composting toilet, as the extraction unit will be fighting against the composting toilet ventilation system flow and may create a back-draft that could leave the room with unwanted odours.

The use of an equalised extraction system is recommended, in which fresh air is pumped in and humid air is pumped out simultaneously. This is done by installing an extraction fan unit in conjunction with an inlet fan unit at the farthest end of the room by the bathing area, such as showers, bathtubs, or other sources of humidity.

This can be achieved by ordering a fan from WCTNZ® at twice the CFM of your room extractor. Most room extractors on the market move around 70cfm.

Passive Ducted Wind-Driven Room Ventilation

Passive ducted wind-driven room ventilation is good for energy saving, but with heavy winds from the lee-ward side of the building it can create a powerful negative pressure in the room and override the composting ventilation system.

If working on a new build with passive types of ventilation, consider the windward flow and positioning of the toilet and bathrooms.

In the case of passive ducted room ventilation, the composting toilet ventilation system energy throughput may need to be increased in proportion to the potential for back-draft. This can be done by up-sizing the fan to a higher wattage and running it in conjunction with a wind-driven vent with optimised specification. See the Passive Ventilation Design Parameters Guide.

This can also be done retrospectively if a problem arises.

Passive Ventilation Through a Window or Skylight

The same principle applies to window and skylight ventilation. Heavy winds can lead to uplift as a result of negative pressure buildup from the roofline, and this can override the composting ventilation system.

If there is a window or skylight in the bathroom, avoid compromising composting toilet ventilation by closing the window and allowing the composting toilet to provide ventilation for the room. The composting ventilation system can be part of the design scope for room ventilation.

Ventilation required by the code is 25cfm room ventilation minimum per toilet fixture. Composting toilet ventilation typically sits around 75cfm.

In the case of passive room ventilation via a stayed window, cracked skylight, or louvred vent, the composting toilet ventilation system energy throughput may need to be multiplied in proportion to the potential for back-draft. This can again be done by up-sizing the fan and using it in conjunction with a wind-driven vent with optimised specification.

Home Ventilation and Central Heating Systems

Home ventilation and central heating systems vary greatly in their design and can be modified to suit the composting toilet system. Generally, these systems are designed to extract air from bathroom and toilet rooms, but they can be modified by the supplier to blow air into the rooms to create positive pressure.

Positive pressure will not affect composting toilet ventilation as long as the pressures and air flows are not too high. In principle, the cfm of composting toilet ventilation should be equal to or greater than that of the home ventilation or central heating system.

Additionally, these systems can be heated, which is beneficial to composting toilet systems in colder climates.

Ask your home ventilation designer to contact WCTNZ® for system design consultancy.