It is true that Passive houses with cathedral ceilings don't show much
temperature stratification, and that is due in part to their extreme
airtightness (max. 0.6 ACH at 50 pa). But air-tightness is only part of the
reason for very little stratification - the extreme superinsulation and
the balanced ventilation through the ERV (or HRV) is the other half of
the story.

If you were to retrofit a moderately insulated house to comply with the
Passive House air-tightness test without adding insulation, you would
still see the temperature stratification, because convection currents
would develop within the house due to the relatively high conductive
heat loss through building envelope cooling the adjacent air, which
would sink to the lowest point, to be replaced by the warmest air in the
middle of the house rising to the peak, to lose its heat through the
roof in turn. The Fairview Ave 2 Urbana IL House cited by Jesse below
has Nominal R54 wall and under-slab insulation and Nom. R82 roof
insulation, far exceeding the recommendations of LEED & Building Green
America.

Katrin Klingenberg, founder of Passive House Institute US,
www.passivehouse.us, and designer of the house, got IBACOS to monitor
the house because they didn't buy her assertions about lack of
stratification and the necessity of all aspects of the Passive House
Standard requirements being met in order to achieve the high performance
levels these homes do. The P.H. Standard is an integrated system for
designing ultra low energy homes using only about a 10th of the energy
of a code compliant house, but you can't achieve the standard of
performance without doing the energy calculations and ensuring that the
building is built or retrofitted to the Passive House specifications
during construction down to the last detail. Many folks are inspired by
Passive Houses and try to get an untrained builder to do one for them
without paying to have the calculations done, and they may get a good
building out of it, but it is unlikely that they'll be able to heat it
with the minimum ventilation air requirement as any Certified Passive
House can. Though Passive Houses are relatively new in the US, the
standard has been refined and tested thoroughly in Europe over the past
decade, and there are now more than 15,000 buildings built or renovated
to this voluntary Standard worldwide, and growing exponentially.

So if you are trying to retrofit a new heating/ cooling system into an
existing high-ceiling home that is not a Passive House and you want
minimal temp. stratification, there are two basic strategies that will
work, and you must decide what you want to accomplish:
1. Retrofit to meet the Passive House Standard, including super
windows/doors, super-insulation, continuous air-tight layer, & ERV or
HRV, and enjoy superior comfort and reliably low energy costs into the
forseeable future,
OR
2. Put your money into mechanical systems and do only modest low-cost
building retrofits like air-tightening (make sure to get all the leaks
w/ multiple blower-door tests, and avoid cold condensation surfaces
within the structure), put in your ERV/ HRV and choose mechanical/
supplemental heating systems that can deal with the convection currents
and stratification that will remain, and budget for the higher energy
bills for the life of the building. Radiant floors in a moderately
insulated building can help minimize temp stratification and draftiness,
since the radiant heat is even throughout the building and is down in
the occupied zone. Ceiling fans or better yet a ducted fan can help move
warm air back down into the occupied zone, but if you don't keep the
airspeed down they can have a negative effect on your comfort through
evaporative cooling of your body in the airstream.

Having been to the Low-income/ affordable Fairview houses and other
Passive Houses in bitter winter weather as well as hot humid summers, I
choose to put my money into a Passive House building envelope, because
it is more comfortable, healthy, durable, and better for the planet. It
really gives you peace of mind to be in a building that can keep itself
warm in winter & cool in summer, even through unpredictable weather and
power outages. I encourage any of you on this list to go the
P.H.Institute's trainings, www.passivehouse.us, and learn how to design
to the P.H. Standard yourself - these are the only affordable buildings
that can meet the carbon emission reduction levels we need to do if we
are to avert run-away climate change in our lifetimes, so we need all
the designers and builders we can get on board.

Join up, I can use the competition and comradery!
Christina Snyder