Many house designs, viewed in hindsight, seem as though the central concept neglects the finer details of function. The house in question here is a good example. It belongs to Bryan Troll, who is rehabbing it. Located in Colorado, the 1980s concrete dome–style structure—with very few windows—is insulated with spray foam. A blower door test measured 1.5 ACH. So, it’s tight.

He wants to make the basement into a separate apartment. He plans to install radiant heating in the floor and a couple of minisplits to handle the minimal AC needed in his region. One of the issues he’s concerned with is ventilation; he’d like to improve indoor air quality with an ERV system, but the house has no ducting, and there’s not much space in which to add ducting. He doesn’t like the idea of exposed ducting, and also doesn’t want to poke a lot of holes in the concrete. He hasn’t had much luck finding a good HVAC engineer, so he’s spent a lot of time reading up on the subject, and is looking for helpful suggestions from the forum.

So, what’s the best way to add ventilation to this concrete dome? That’s the topic for this Spotlight.

Central ventilation system

Paul Kuenn and Michael Maines both recommend an ERV made by Lunos; it is lauded for its efficiency and can be a problem solver in cases like this. While Kuenn writes that it requires just two 6-in. holes in the walls, Maines notes that they can be a little noisy. Regarding Bryan Troll’s ducting limitations, Maines suggests using metal spiral ducting, which has low visual impact when exposed.

Dennis Wood agrees, and says the supply and return should be as far apart as possible,…