How low can you go ( storage temp )

jebatty said:

What do the trees say in -30F? ... crack - split, split - crack, crack - split.

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The first year we had our log house on our basement it was unheated and open to air,shed dormers had no ends in them.We had a few cold spells and we would hear some of the logs crack and it was like a gun shot.Got used to it after a while.We live/lived in the basement at the time.
Thomas

For those of you approaching -20F and lower, the lower the better, time to boil a 1 quart pot of water and then take the boiling water outside and fling the water in a giant upward swoop. Enjoy the instantaneous sublimation of the water into a cloud of vapor. If you haven't done this before, try it, gather your friends, and watch nature's drama.

CAUTION: If it's not cold enough, you will have boiling water flying through the air and you don't want it to land where it may injure someone. This may work at higher temps than -20F, but be careful. At -20F and lower it works very well.

Many overlook sublimation. That's why they think their wood only dries in the summer.

(Sublimation (of ice) to vapor is invisible.)

True ... would it be more precisely accurate to say that what happens is that the high level of water vapor in the very cold air reaches the dew point instantaneously and the vapor condenses immediately into a cloud rather explosively?

jebatty said:

True ... would it be more precisely accurate to say that what happens is that the high level of water vapor in the very cold air reaches the dew point instantaneously and the vapor condenses immediately into a cloud rather explosively?

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Just spent a while googling the phenomenon and could not find any explanation that made much sense.

Everyone seems to agrees that the air needs to be below 25 degF or so. The water vapor saturation curve for air below 0 degF is just about as flat as you please, so it's fair to say little if any dry water vapor is involved at all. All there can be is water droplets, ice droplets, and perhaps some tiny amount of crystal deposition of water vapor (snow).

From the pictures it looks like large water droplets traveling in trajectories that leave behind tiny water droplets, which in turn freeze into tiny ice droplets. Maybe there's no tiny water droplets at all, it could be the big water droplets form shells of ice that shatter away as the ice expands rapidly.

Since the air is already saturated with water vapor, there is little or no evaporative cooling of the air, rather, all the energy from cooling the water to the freezing point, and all the heat of fusion is going into heating the air. Heating the dense air rapidly causes it to expand rapidly, and so my guess is that this somehow turns big droplets into tiny droplets in a hurry, but again, I haven't found a satisfactory explanation of just what is going on. (Although it's fair to conclude there is no sublimation involved.)

ewdudley said:

(Although it's fair to conclude there is no sublimation involved.)

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Perhaps not in the overall scheme of the experiment but on the molecular level there has to be some sublimation involved. Take a block of ice, no, lets compare it with something that doesn't disappear in the summer. A split log sitting there and water molecules are dancing within and on the surface in both summer and winter. In the summer they're dancing higher and faster and in the winter they're dancing lower and slower. Sublimation occurs when the air surrounds the molecule and absorbs it. In the winter the lower and slower molecules probably don't get absorbed as quickly but one advantage they have is that the air is much dryer and just can't wait to suck up that water molecule. In the summer the molecules that are dancing high and often but the air is more moist which slows down the absorption.

This was too low for me. House temp fell a few degrees. Loaded her up at 6pm the night before. Should have topped off before bed. -8f and windy, coldest night with boiler to date. Took 200#s of wood throughout the day to satisfy demand and bring 1000gal storage back to full charge.

why i didnt listen and install return protection to start, who knows. anyone trying to save money, this is not the area to do so. back to topic.

full output from what i have seen from my boiler is 160 with the wood i am burning. storage was 155/140. let the fire die at 6 last night, granted we were 25-35 degree throughout the night, woke up this morning at 5 and storage was 120-110. it wasnt that cold out but did leave the t-stats up to 70 and baseboard circs almost no stop as i can't seem to keep that satisfied with my boiler temps.

I saw -15 on my truck when I left for work this morning. I need about 12 hours of burning to keep up like this. I start my fire at 6pm with a 1/2 load, 2/3+ load at 7:30ish and then cram it full at 10:30pm. So far so good. This schedule would not work with low btu wood, however. I have to avoid grabbing the boxelder for the time being.

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I have forced air HX as well and much the same schedule, but I fill twice before bed when we are below 0, So about 1/2 a chamber each time. I operate mostly from 165 down to 110 when it is this cold we start the fire at 115 and it is about 105 before the boiler starts to build enough heat to charge things back up.The tank will last about 14 Hours this way. The air registers in the house consistently deliver 15 degrees below the water temps so 100 degree water gives me 85 degree air. I have the high efficiency/ "low air temp" furnace that helps with this setup.

One note before I had the boiler it hit -10 for a spell and my "efficient" furnaces simply could not keep up, the house was at 66 and falling, we were using the fireplace to make up the diff. Now all is great. If I want 150 degree air at the register I start the boiler ... no more worries!