The yard does most of the work and none of the spending
Take a pack going on the sticks at 70 percent, a yard that bottoms out at 15 percent, and a 7 percent target. The whole job is 63 points. The yard does 55 of them — 87 percent — and the kiln does the last 8. Because moisture content is measured against oven-dry weight, water is strictly proportional to it, so the yard also sheds 87 percent of the water: on 3,000 board feet at 45 lb per cubic foot that is 3,640 lb of water out on the yard against 529 lb in the chamber.
The money runs the other way. At $9 per thousand per month and about 12.7 months on the sticks, holding the pack costs $344. The kiln run at $150 per thousand costs $450 and takes a few days. Per point of moisture removed, the yard is $6.25 and the kiln is $56.25 — nine times more expensive per point, for a job an order of magnitude smaller.
Why days per inch and points per week give different answers
They are two different measurements and they disagree unless you make them agree. Days per inch says a 1-1/16 board takes 388 days regardless of how far it has to fall; points per week says the time is however long it takes to shed the points at your rate, so a wetter start means a longer wait. The first is a habit; the second is arithmetic. If you have weighed a pack, use points per week, because it is the one that responds to the actual drop.
The year-per-inch saying is not a measurement at all. It is a memorable sentence that happens to land near the truth in a temperate climate for a moderate species and is badly wrong in a dry one, which is why the figure sits in a field on this page rather than in the code.
A month of standing still costs the same whether it dries or not
Holding 3,000 board feet at $9 per thousand is $27 a month, forever, and it does not care what the moisture meter says. That is the number to hold against any decision to leave a pack a bit longer. At the front of a run a month buys a great many points; at the end it buys almost none, because the drying curve has flattened out. The calculator prints the average rate against the month cost so the comparison is at least in front of you, but it labels the points as an upper bound, because an average rate always overstates what the tail of a run will do.
What the yard floor really is
It is not a wood property. It is the moisture content your climate holds wood at, which is set by the humidity your yard sits in across a year, and it is the reason air drying alone gets furniture stock nowhere near a heated interior. Two mills a hundred miles apart can have floors four or five points different, and the difference lands entirely on the kiln, which is why the field asks for your own meter reading at the end of a past season rather than offering a number.
Questions people ask
Why does the days-per-inch mode ignore how wet the lumber is?
Because that is what the rule is: a length of time per inch of thickness, from green to wherever the yard takes it. It is a rate of thickness, not a rate of moisture, and it says nothing about a pack that goes on at 40 percent rather than 90. That is a genuine weakness of the rule rather than of the page, and it is why the points-per-week mode exists. If your records are in days per inch, use that mode and read the answer as the usual figure for that thickness.
Does the calculator know anything about season?
No, and it should not pretend to. It adds calendar days to the start date, so a pack that goes on the sticks in October gets the same number of days as one that goes on in April, which is not what happens in any climate with a winter. If your records show a strong seasonal effect, run the page twice with two different rates and treat the answer as a range.
What if my target is above the yard floor?
Then the kiln has nothing to do and the page says so — it reports zero points and zero water for the kiln side and the whole drop happens on the sticks. That is a real situation for construction stock and for anything staying outdoors, and it changes the economics completely, since the entire job is then a carrying cost rather than a fuel bill.
Why is the water split exactly the same as the point split?
Because moisture content is water weight divided by oven-dry weight, and the oven-dry weight does not change as the wood dries. Water at any moisture content is that fixed dry weight multiplied by the percentage, so a drop of one point always sheds the same weight of water regardless of where in the run it happens. That is a genuine and slightly counterintuitive property of the oven-dry basis, and it is one of the reasons the basis is used.
Should the carrying cost include the risk of losing the pack?
That is your call and it belongs in the figure if you want it there. Weather, staining, insects, a pile that shifts, and stock that goes out of fashion before it is dry are all costs of holding rather than costs of drying, and a mill that has lost a pack will carry a very different figure from one that has not. The field is a single number precisely so you can load into it whatever your own experience says holding costs.