The house as a system…air

Air movement in a tiny house is a bit of a balance. You want to make your tiny house as tight as possible to manage the interior air temperature and humidity, but if you make it too tight–without provision for fresh air exchange–the air inside your tiny house could become loaded with pollutants and volatile organic compounds (VOCs). Some issues with pollutants and VOCs can be reduced by selection of appliances (ex. gas appliances obviously have greater potential for combustion pollutants) and careful selection of materials. Learn more about air flow in a house here.

Living completely off the grid probably means relying on gas appliances, gas heat, and gas hot water heating. A tiny house designed to hook up to a 30 or 50 amp outlet must still rely on either propane or solar to supplement energy needs. Propane does not burn 100% clean so there must be a provision for ventilation.

So, the design and construction of a tiny house begins with the idea of reducing air flow INTO (summer) or OUT OF (winter) the house. Assuming you have not created random holes in your wall or ceiling, most air will be moving through holes and gaps around windows, doors, plumbing, and wiring, and NOT through the walls in general. Between the exterior siding and interior paneling, its unlikely a lot of air will get through. If you minimize intrusions through the walls, floor and ceiling for heating, water, waste, and gas and fill the space around those intrusions with tape or “foam in a can” you can stop much of the air flow flow. Modern windows and doors are designed to reduce air flow if installed properly, which is one argument in favor of not using old windows and doors (at least not without “modernizing” them) in the tiny house.

So, now that the house is relatively air tight by design, it’s time to consider how you will control or manage fresh air coming into the tiny house. We have that pretty well-covered in the Tiny Dawg House because we are using a very efficient mini-split heat pump that will “condition” fresh air as it comes in to be sure the new air will not significantly alter the interior air temperature.

We have also planned in two ways to vent air and remove unwanted gases (of all types) by using a composting toilet (Separett) with a built in vent fan–more on the composting toilet in a later post–and a second vent somewhere in the kitchen near the propane range to insure any products of combustion are escorted out of the house before they become a problem. We also choose to use a propane hot water heater that will be placed OUTSIDE of the tiny house. While this could pose a problem of freezing (hard to imagine in Georgia) it does place the source of combustion outside our relatively airtight tiny house and eliminate the need for vent pipes that can also leak.

Will this be enough? It’s hard to say. An engineer could probably calculate the exact balance of air in our tiny house, but the numbers would still depend on how the house is used– i.e. number of times the entry door is opened, how often windows are opened, the amount the propane range is used, and the settings in the mini-split system.

There are a few issues we won’t have in a tiny house that could be a problem in a regular house. For one thing, there is only one interior door that will likely be kept open much of the time. Interior doors, if tightly sealed, can actually have a negative impact on whole house air flow. The tiny house is also so small, and intrusions in the envelope so few, that it’s highly unlikely to miss a spot when filling all the gaps.

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