An earth tube is a buried ventilation duct. The idea behind burying ventilation ducts — the ducts conveying fresh outdoor air to a building — is that the soil surrounding the ducts will warm the ventilation air during the winter and cool the ventilation air during the summer.
Earth tubes can work, as long as:
- the duct is installed in a climate with useful soil temperatures,
- the duct has a large enough diameter,
- the duct is long enough,
- the duct is buried deep enough,
- the duct is installed in a way that minimizes potential condensation problems,
- the duct is able to exclude radon.
That said, earth tubes are expensive to install, so they are rarely a cost-effective way to condition ventilation air.
Poorly designed earth tube systems are probably more common than well designed earth tube systems, which is why many earth tubes are eventually capped off and abandoned. If you are considering installing an earth tube, it’s worth learning about what works and what doesn’t.
Get the details right to avoid mold
Earth tubes have a mixed reputation, and it’s easy to find published reports of successes as well as failures. Full disclosure: I’m not a fan of earth tubes. If I wanted, I suppose that I could cherry-pick scary stories from among published anecdotes, but that would be unfair. If you want to install an earth tube, and you do your homework before installing your system, there’s no reason to think that ventilation air delivered by your earth tubes will be damp or mold-infested. Some earth tube systems work well.
The main problem with earth tubes is that even when builders install a well-designed system, the energy savings are so low that it’s hard to justify the high installation cost.