"daestrom" wrote in message
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wrote in message
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daestrom wrote:

If it only leaks 0.4x2400x8x0.075 = 576 lb/h (128 cfm, vs ASHRAE's 15 cfm
per occupant fresh air standard), humidification expends 5.3X the savings.

US houses leak way too much air. Air-sealing raises indoor humidity and
actually saves heat energy.

Probably true, but doesn't ASHRAE have a minimum recommended ventilation
level to control pollutants?

That's the 15 cfm/occupant above...

Just looking at the '400 Btu/hr-F' figure, to get that with 0.7 ACH, we have
about 244 Btu/hr-F to warm up the fresh air coming through, and 156 Btu/hr-F
actual conductance. For a 49x49x8 house, that would be something like R-40
in the ceiling and R-16 in the walls. Over half the energy is lost through
the air leakage portion.

US houses leak way too much air, enough for 244/15 = 16 full-time occupants
on a cold day, with no fresh air at all on a mild day.

Even the 'tight' 160 cfm for the theoretical house we've been discussing,
that's still 160/15 = 10+ full-time occupants.


Is there any practical way to measure a house's air leakage? I've seen the
'fan-in-the-doorway' trick used to find drafts, but does it actually
*measure* the leakage?

Yes. They pressurize or depressurize a house to 50 Pascals using a $50
Magnehelic gauge and measure the leakage as a pressure difference across
a calibrated orifice in the door. Natural air leakage is about 20X less
than the measured leakage at 50 Pa.


I was looking for something that would measure *actual* leakage, not some
number at 50 Pa. To get an idea of how much leakage actually occurs on a
typical winter day. 'Natural air leakage is about 20X less....' doesn't sound
as accurate as some sort of direct measurement under typical winter conditions
(in winter, I try to keep the windows and doors closed, not open with some fan
deliberately drafting on the house ;-).

The short story is that it isnt possible to measure what you want
to measure without rather extreme measures like say special
isotope tracer gas and monitor the isotope ratio as it leaks away.