How I Built a Net Zero House

February 17, 2023: That’s how I’m going to start and then I’m going to talk through it step-by-step to whoever’s interested at the upcoming Duluth Energy Design Conference, on February 21st. This will be the furthest away and most professional audience I’ve presented to and I’m pumped to do well.

I’ve had a few “issues” now that I’ve gone through 3 winters…..and I have data. I’m going to fess up about some problems with condensation and uneven heat. And I’m going to brag about my net-zero status and how truly blessed I feel to live here.

In my first winter, I had liquid condensation and chunks of ice clinging to the corners of my windows during cold snaps (let’s say 10 degrees and below). I wiped it down, ran fans, and chalked it up to the conventional wisdom that “it takes 1-3 years for a new house to dry out”.

But I had the same problems the second winter and now this one. My big revelation came when I borrowed a good humidistat (no, the hardware store one wasn’t accurate enough) and compared my house with Dave’s.

Dave moved into his new house next door last fall. It’s very similar to mine: slab on grade, 12″ thick double stud walls with dense pack cellulose, a super-insulated ceiling, Marvin fiberglass windows with standard glazing, and MemBrain installed as an interior air barrier. He heats with a Mitsubishi Air Source Heat Pump (ASHP) like mine and brings in fresh air with a Lunos Heat Recovery Ventilator (HRV) like mine. But he’s had no window condensation and certainly no icing.

The only thing we could think of is that he doesn’t have house plants. Yet.

It could be that, or it could be that he runs his HRV on high. I usually run mine on low because on high it’s too noisy. He also has his ASHP located in a more favorable position: in the main room on the lower level, not in the loft like mine.

In any case, the humidistat told the story:

Amber: Relative Humidity 38 – 45%

Dave: Relative Humidity 20 – 25%

I’ve since adopted more aggressive tactics (no, I haven’t thrown my plants out in the snow). Running my HRV on high and running a small fan in the loft on high to better distribute the heat pouring out of the the ASHP, I was able to bring the humidity down to 30% (but it liked to go up to 36% when I wasn’t looking). Now we just need a cold snap to see what the windows do. But you probably don’t want that and I don’t blame you.

A happier topic is the data on my solar production. I’ve updated the “NET ZERO” page on my website, and if you’re wondering whether it’s possible to go all-electric and ditch fossil fuels, check it out!

4 Comments on “How I Built a Net Zero House

  1. This is the builder I was telling you about the other day. I don’t know why I get these emails but I’m interested in her ecological building process and she sometimes has open houses when she completes a project. Would be fun to take a tour.


  2. Hi Amber- I thought keeping the humidity around 40 -50% was the goal we should be seeking. I use a humidifier to raise my humidity in the winter. If I don’t, I get nose bleeds and start coughing. Even so, it’s hard for me to get above 30%. Of course I do use a wood burning stove which does dry the air quite a bit. And my plants like the higher humidity too. My house is not as energy efficient as yours so that may be the difference.


  3. I have to say that a relative humidity of 20-25% is not very comfortable to live in! We try to keep ours around 50 in the winter, although I turn off the humidifier in the winter when the temperature drops below 15 and/or if I start to see condensation on the windows. Those low humidities are really hard on any wood furniture or on a piano, as well on our own skin!


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