Calculators
Plumbing calculators: inputs you already have, one formula, one answer, with the formula printed so the number can be checked.
Each calculator takes numbers a homeowner already has, applies one formula, and returns one answer. The formula is printed on the page so the result can be checked by hand.
Heat cable sizing calculator: how much self-regulating cable a pipe run takes, and whether one breaker will carry it
Chemelex's formula is pipe length x spiral ratio, plus 4 ft per globe valve, 2 ft per support, 1 ft per power connection. Its own 50 ft example needs 78.0 ft.