It can be a valid issue. Assuming you store your jars with the rings off as recommended then stacking them directly on each other is discouraged as it can contribute to seal failures. But stacking boxes is no issue normally.

When it is jars out of boxes then it's recommended that a layer of cardboard or a thin layer of plywood be used between the layers of jars so there is no direct contact and the weight is more evenly distributed over the lower layer. So stacking boxes would have the same effect.

Dave

I've been using a certain size box that fits 15 pints, I had source for plenty. I would stack 2 layers but not more than that. No problems so far, over 4 years now.

I love to have my shelves set at just over qt and pt heights, but haven't got that done in new house yet.

Marla

Thank you for your responses. I thought the way I was doing it was fine but then my friend said it wasn't ok and I started to think maybe it wasn't. I looked on the NCHFP site but couldn't find anything about stacking jars. I could have missed it though. I knew someone here would have a reliable response. It is so great to have this community. Thanks again!
Tina