Is there a penalty if I withdraw from my FHSA for something other than buying a home?

Not a separate penalty, exactly, but there is a real cost, and it's easy to underestimate. A withdrawal from your FHSA that isn't a qualifying home purchase is generally included in your taxable income for the year you take it out, the same way ordinary income would be. Unlike a qualifying withdrawal, which comes out completely tax-free, a non-qualifying withdrawal loses that tax-free treatment entirely.

It's more accurate to think of this as the FHSA's growth and contributions simply becoming taxable again, rather than a fixed penalty tax layered on top. That distinction matters, because the actual cost to you depends on your income tax bracket in the year you withdraw, not a flat percentage - a withdrawal in a high-income year can cost considerably more than the same withdrawal in a lower-income year. Before withdrawing FHSA funds for a purpose other than a qualifying home purchase, it's worth remembering that the tax-free rollover to an RRSP or RRIF, covered in a related question, is usually the better option if you're simply changing your plans rather than needing the cash right away.