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Old 03-20-13, 02:28 PM   #4
Apprentice EcoRenovator
Join Date: Aug 2012
Location: California
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Well, I guess a good discussion thread begins with more than one point of view. So I'll represent that different point of view.

Stale air with higher than recommended CO2 buildup always happens in houses occupied by humans. I live in northern CA also so I'm aware of your dilemma. I live in neighboring Lake county. There are two main aspects for deciding on whether to get an HRV, besides the high expense of a non DIY unit. The first is the total amount of whole house air exchange your new house will have with a 50 pascal blower attached to the door. A PassivHouse rating is about .5 per hour or thereabouts. I forgot the exact number. However many people think that airtightness under around 2 air exchanges per hour has diminishing economic returns. A house with a rating of 2 or better is colloquially described as a "pretty good house".

That brings up the second determining factor. We don't live in a real cold climate, though its colder in northern california than most easterners realize.
It makes more sense to pay for an extremely tight house in colder climates. For one thing, the temperature differentials inside and outside are bigger which means more temperature is being lost in winter. If you are just building a pretty good house, which makes economic sense in pretty much all of California except the high Sierras, then you will have enough random leakage that a Panasonic whispergreen bathroom fan will make a lot of sense. They can run all day at 30 or 40 cfm using only 3 or 4 watts. So you're not wasting a lot of electricity. With an HRV you are going to be using a lot more power than that and because the temperature differentials inside and outside are not as extreme here the energy reclaimed in the HRV will not be as good as when it is used in colder climates.

I realize when building a new house it feels best to go for the tightest house you can build. If you get to PassivHouse standards you probably will need an HRV because their won't be enough random air leaks to provide the return air for a simple exhaling ventilation fan. At .5 you are likely to get stale air, and high indoor CO2 and high humidity that only an HRV can control.

But as I said, its overkill in our climate. If I was in your position and you do a blower door test I would try to get a house that leaks less than 2 but greater than, say 1, at least ideally. You can then get away with just a simple Whispergreen fan in the bathroom, assuming its a simple single floor building with a somewhat open floor plan. If it ends up being in PassivHouse territory then you might be forced into an HRV. A needless expense in California (in my opinion).
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