Properly Venting a Tiny House
Do-It-Yourself builders actually do a great job of constructing tiny homes. Every crack is carefully sealed, every gap insulated. The DIY builder can actually do too good a job causing oxygen levels to get dangerously low and humidity trapped inside creating a host of issues. Properly venting a tiny house is an essential design aspect to consider.
Dangerous Humidity Levels:
Each day a human body expels 3.5 cups of water thru respiration and perspiration. The shower, a ventless washer/dryer combo, and cooking add additional humidity. This moisture is easily dispersed in a larger home. But within the small volume of a tiny home this moisture becomes a serious issue. On a cold day you’ll see this moisture condensing on the windows, poorly insulated areas, and other areas like cold water pipes and wheel wells. Dangerous black mold can quickly take hold in these damp areas. The goal of properly venting a tiny house is to reduce this humidity.
Indoor air quality:
Any appliance that uses combustion uses oxygen. Often these appliance have an outside air source but a kitchen range, some wood stoves and other heating options like kerosene heaters do not. They will use the room oxygen. This oxygen needs to be replaced by venting or serious health consequences for the occupants will result. In addition to the dangerous health effects low oxygen level produce, stifled combustion will create deadly levels of carbon monoxide and other deadly gasses. Carbon Monoxide detectors are required in all homes. This is even more critical in a tiny home.
Replacing oxygen without loosing heat:
There are warning signs in my RV to open the door and roof vents when using the propane cook top. I also leave a window partially open all night to avoid the moisture buildup. Opening windows and doors is a good way to address poor indoor air quality if you live in a warm climate. In the high mountains the temp can get down into the thirties most nights. To avoid running the furnace all night we sleep in really good sleeping bags and even wear a hat. We kick the heater on about an hour before we get up but it can still be pretty cold. This is fine for a weekend camping trip but might get old after awhile.
Enter the HRV (heat recovery ventilator) and ERV (Energy recovery ventilator):
Energy (or Enthalpy) Recovery Ventilation will retain much of the humidity inside the structure. In the summer this humidity transfer is reversed. An EVR is better in hot, humid areas.
The Panasonic FV-04VE1 WhisperComfort™ Spot ERV Ceiling Insert Ventilator offers a revolutionary way to provide balanced ventilation with a ceiling insert ERV. This unit provides a low rate of continuous air exchange. It supplies fresh air to replace exhausted air helping to balance air pressure within the home. It is in-ceiling mounted, as seen in the video below, and can be mounted above the shower. In this video the unit is cleverly modified to suck old air out of the bathroom and introduce fresh air into the adjacent living room.
The Fantech VHR 150 Heat Recovery Ventilator (HRV) can be used in colder climates to preheat the intake air
so you save on energy costs, while during summer, the incoming air is pre-cooled if the house is equipped with an air cooling system. You will need the Electronic Programmable Wall Control shown on the right.
Both of these units are designed to run 24/7 so care the installation location should be given careful thought so you don’t hear it running near the bedroom at night.
A gas range uses oxygen during the combustion process and creates hazardous gasses like carbon monoxide. A range hood, vent to the outside, is an essential appliance for a tiny home. Most range hood are thirty inches wide or more but this Miseno MH80120AS 390 CFM 20 Inch 3-Speed Ultra Quiet Range Hood Insert with Halogen Lighting is only 20″ wide. Perfect for a tiny home application.
Properly installed, this range hood vents harmful gasses outside.
Make-up Air is an essential element to your ventilation system
As your exhaust fans vent harmful gasses out of the house you must also have a source for fresh air into your tiny home. Fresh air vents can be a safeguard from the backdrafting (the act of pulling gas, carbon monoxide, and/or smoke back into the house) of toxic combustion by-products. They also prevent drawing air from nasty places like the composting toilet.
See more on make-up air, venting, passive solar air intake heating, and intake HRV in my blog post.