Thursday, January 3, 2013

We Have Settled In

December was a month for experimenting.

Over the summer we had used the heat pump just enough to keep the humidity level at 50%, which also kept the indoor temperature around 72-74°F. The PAHS tubes were not hooked up until November, so the surrounding thermal mass probably had not heated up as much as it might have. Then we were away the second half of November, which gave the house a chance to cool a little more.

When we arrived home December first, the average indoor temperature was 68°F. Now the average indoor temperature is 72°F. A month ago the average outdoor temperature was about 20°F warmer than now. Currently the typical indoor air temperature drops to around 71°F at night, and with one exception it rises to 72-73°F in early afternoon. The exception is when the sun shines in brightly through all those windows, and the temperature then peaks out at around 75°F in early afternoon. The thermal mass quickly absorbs this extra heat, and by early evening the temperature is back to around 72-73°F.

Every evening around 5:00 PM we close the insulated drapes, and we open them again just as the sun is beginning to show on the horizon. On cloudy and rainy days we may not open some or all of the drapes during the daylight hours. We still receive considerable light from the upper windows and light tubes, and almost never do we need supplemental light during the daylight hours.

Our current routine with the masonry stove is to fire it up every evening around 6:00 PM and again around 6:00 AM if the day is predicted to be cloudy. Much of the extra heat from the stove and sun is being absorbed into the thermal mass, either through contact with the walls and tile floors, or by warm air flowing out through the tubes and the heat being absorbed into the surrounding soil. The extra heat is slowly increasing the surrounding thermal mass's mean temperature, and we are seeing that in the smaller daily temperature fluctuations around the ideal 72°F value.

What a difference 4°F makes. 72°F still feels a bit cool to me, but it is very tolerable. A 72°F ambient temperature is not nearly as noticeable as a 68°F or 76°F temperature. I look forward to the occasional overshoot to 75°F when the sun is shining. It is enjoyable to soak up the sun's rays, knowing that it is 50°F or more colder just outside that window.

I think that the thermal mass's temperature is slowly being brought into equilibrium with the desired comfort-zone temperature, and we will soon be firing up the masonry stove less. That is too bad, because I have cut so much wood, and I kind of like playing with fire. We may get down to firing the stove once a day by the middle of January, and then once every other day by early February. Last year I think we pretty much stopped firing up the stove in early March. That is about the time to start bringing down the thermal mass's mean temperature in preparation for the cooling season.

Ah, cooling season again and back out to sweating in the garden.


  1. Thanks for the link to your blog that you posted in the comments on my blog:

  2. Roger,

    I have an important mail for you regarding PAHS, because it's confidential I don't want to write it as a comment, could you please reply on this mail : antoine.strauss(at)

    Talk to you soon,

    Antoine Strauss

  3. Hello Roger. We are planning to build an underground home on our property in the midwest and are really interested in your PAHS system. We would love to see your system if you would contact me at my personal email Thank you Roger.

  4. It's a very interesting and helpful information. Thank you for sharing.

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