Thinking ahead just in case it blows...............

The issue is length - I could measure the outside dimensions of the tank,
but without taking the element out there's no guarantee there's no
obstructions inside - and I could just measure the element if I took it out.

The easy way out is to buy one of the shorter folded elements, but I'm
wondering if the effect on convection would be good or bad.

The tank is square, not cylindrical.

Thanks for any help.