I'm quite sure they would not replace me just for one vacation per year, though personally I would also prefer to work less overal and in that case I'm not so s

I'm quite sure they would not replace me just for one vacation per year, though personally I would also prefer to work less overal and in that case I'm not so sure they would not find rather someone else, because this job requires extreme consistency in results. And besides quality I guess one of the main reasons why they stick with me for years (because they sure could find someone cheaper) is very fast response time and basically zero downtime. All in all I didn't complain about job, I just complained that my workload is more than I would prefer and can't really do much about it. But mostly I was looking for recommendation what would be the best way to take vacation under these circumstances, if I should just take vacation and work during vacation, hoping to find few free hours in morning or afternoon or sacrify completely lost income (though I think that would make me uncomfortable knowing I am doing nothing throwing money I could earn out of window and someone else is earning them possibly building position for himself to replace me).