Sunday, February 24, 2013

How Did January and February Go?

This winter was considerably colder than last, and we burned more wood. But we have enough seasoned black locust and hedge apple to last several years, so why not use it? We have fired the masonry stove an average of about 1.5 times per day, probably burning about 75 pounds of wood per day. The wood is very dry and the fire burns extremely hot and fast. The two-inch iron pipe we added to the masonry stove to allow combustion air under the grate after the fire has burned down works perfectly. As I had hoped, it reduces the burn-time by about an hour or more, allowing me to close the damper sooner and save heat for the house.

The good news is that our house has been considerably more comfortable this year than last, perhaps because I had hooked up the PAHS tubes a while back. But the PAHS tubes have not worked the way one might expect. Outside air has always come in through the lower cold-air tubes, ever since I hooked them up. The average temperature of the incoming air has risen slightly to around 66-68°F, and this is only noticeable when right next to a register. But the thermometer on the thermostat in the hallway doesn't mind. During the day it registers between 71-74°F and at night between 68-71°F. Consecutive sunny days push the reading toward the high end, and consecutive cloudy days push it toward the low end. So our thermal mass is doing an excellent job of smoothing out the 24-hour fluctuations.

Now a bit about the sunroom. It is sandwiched between the north wall of the house and the garage's south wall, and it is on the east side the entry room where the masonry stove is located. It faces about 20° south of east. Its east-facing, sloped roof is entirely of clear, double-layered, honeycombed panels, the same as used in greenhouses. Its east-facing walls are mostly glass. The sunroom has a ceramic tile-covered, concrete slab foor and brick walls on its south and north sides adjacent to the house and garage. This thermal mass stores a tremendous amount of heat when the sun shines in, and slowly releases it otherwise. Several times this winter we have had temperatures near 0°F, and the sunroom temperature hasn't fallen below 40°F with no supplemental heat. We have a number of plants in the sunroom, and they are happy, some even blooming.


  1. Hello Roger,

    As always, thanks for taking the time to document what is essentially a very rare experiment.

    I'm intrigued by your earthtubes which are pulling in air through the lower tube in winter, whereas according to Hait air should be going OUT that tube when the house is losing heat.

    This is from Hait's book:
    "Earth tubes connected as in figure 46, DO NOT operate on the temperature difference between the inside and the outside of the home. They work because of the difference in temperature between the HOME and the earthen STORAGE ZONE. That is why the outer openings of the tubes exit the earth AT THE SAME LEVEL. But even the lower earth tube must have a slope to it for it functions like the thermal syphon, which is a heat trap.
    Like Chillie Willie's door, earth tubes should always have an altitude difference, because they too must function as heat traps."

    I wonder if this has something to do with the amount of heat you are adding INTERNALLY with your masonry stove, which could mean that the home is actually still warmer than the storage zone?



  2. Hi Bruce,

    I believe what you say is correct. I hadn't properly connected the air tubes until last fall, so the surrounding soil may not have heated sufficiently last summer. Also I used a heat pump last summer to keep the humidity around 50%, which required pushing the indoor air temperature down to 72-74°F so that the air conditioner would run long enough. So cooling the interior in the summer to lower the humidity and heating it in the winter may defeat the whole purpose of using passive air tubes for heating and cooling.

    I think Hait assumed that heating and cooling would come primarily from the surrounding soil. But our heating is primarily solar and the masonry stove. And our cooling is primarily the heat pump at little energy cost. (Roughly July through August.)

    I have been considering installing a reversible fan at the inlet to one set of air tubes to control the airflow. Then I can experiment to see which direction gives better results.

    In any event, we have been happy with the house's performance this last year. The temperature extremes were 66-76°F, where normal is 68-74°F. A twenty-four hour swing rarely exceeds 4°F, so the house always feels comfortable.

    Best regards,


  3. Hello,

    We just discovered this blog and PAHS. My husband and I have been planning a conventional Passive house for a couple of years now but a change in building sites was forcing a plan review. Our blog is here. to read who we are and what our plans were.

    We discovered the idea of PAHS (I am still reading the book) but in contacting several architects were told that this technique is unproven at best. Don Stephens AGS would allow us to keep beloved design details but he doesn't return calls or emails so no luck talking to him (yet). Then I found you. Would you be willing to have a dialog about some specifics of how PAHS functions in the real world in your experience? I am still reading/absorbing your posts but there is hope now that we could build our home (modified) and add PAHS elements correctly now. I thank you for putting this out there. I plan on also contacting Davis Caves for info as well.
    I hope that you have a desire to respond.

    Paige Hads.

  4. Hello Paige (or should that be Hads?),

    You could try the Underground House group on Yahoo:

    Several participants have knowledge about PAHS, and Tom in particular, having built several successful PAHS houses.