Build Tight. Ventilate Right.

When we built our house we decided to have an Energy Star rater calculate the HERS score for the house (11 was it? 12? Not that I verified that they used the right numbers for our insulation, etc, but OK, not bad.) And part of the Energy Star Homes process is that a blower-door test is done to determine how leaky the house is. Since that’s the other way one can lose heat/coolth from the house. Not just thru walls and windows and doors, but from actual airflow thru all the cracks.

Well anyway, our house is quite tight. It was 200 CFM50 which works out to

200 CFM50 * 60 min/hr / (2310 sqft * 8.2 ft/floor) = 0.63 ACH50 (air changes per hour at 50 pascals)

I don’t know if I’m using quite the right volume for the house (that’s 2310 including basement) but if so, that is JUST shy of the 0.60 ACH50 needed for Passive House certification. Nice. We’re probably a bit worse than this, but really, I can’t complain given we are using mostly double hung windows and double hungs don’t seal up as nicely as casements.

It was the tightest house the Energy Star person had tested in 10 years or so of blower-door testing. I believe our house is apparently what is called a “Tier 3” / “Tier III” certified home for Energy Star Homes.

In New England, I reckon we are one of about a few dozen or so such energy efficient homes. Something like that.
Here’s a list I am compiling. More at the NESEA.org Green Buildings Tour website I am sure.

Ventilate Right

The idea of Building Tight is that it is actually better for
– durability
– indoor air quality
– saving money

Durability: fewer mositure/mildew/rot problems because there is little concern with
1) moist summer air driven from outside to in
2) most winter air (since outside is very dry) being driven from inside to out.

Indoor Air Quality: Instead of relying on leaks in a closed up house (in winter or summer) to provide fresh air, one can bring in exactly the right amount! And filter it to your heart’s content! And put it right where you want it!

Saving Money: The idea is this… in the winter for example: instead of 68F air exiting the house and 25F air coming in…. thru leaks… one can instead use an HRV (heat recovery ventilator) which is essentially a fancy air-to-air heat exchanger. The incoming and exhausting air cross paths in a fancy cross-woven area and 60 or 70% of the heat that would be normally lost is recovered and plunked into the incoming air. Clever! One has to factor in the cost of installation and running the fan, but the fan costs almost nothing, and the control over the IAQ and durability is worth it.

Some others recommend slightly different approaches:
– not building QUITE as tight (but still 10x tighter than a typical house)
– using Panasonic Whispergreen bathroom fans on timers or humidistats or CO2 monitors to do “exhaust only” ventilation.

Lots more on this topic over at greenbuildingadvisor.com — free blogs and Q&A sections. I sound like an advertisement I know. Sorry, it’s a very helpful site!

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