If he's not paying you anything, then there are no room and board expenses and so you are not making a qualified withdrawal from the 529.
Is this where the gifting camfused brings up comes into play? In the other direction?
I think this line of reasoning is weak. However, as I mentioned elsewhere on a 529 thread, as long as you're not doing something incredibly wrong/bad, it's extremely unlikely that anything would ever come of it. The IRS simply does not have the resources to verify every 529 withdrawal and confirm where the funds actually went. So, at the end of the day, if you are comfortable with what you are doing, keep good documentation, and can justify what you've done in the unlikely event you are audited, then that's all that matters.
I had read pub 970 quite a lot, and was going to write a spirited defense of my position, but in reviewing the relevant section I had missed the phrasing at the beginning of the paragraph in 3a where it says "Expenses for room and board must be incurred by students..."
Certainly one could argue that he has "incurred" expenses because he's eating food, which costs money. The board question is a little more ambiguous, as he's living in my house, which I owe outright. But I do pay electricity/water/gas/sewer/trash, which are actual expenses and things he uses. And as mentioned above, in neither case do I charge him for any of these things. What I don't know is whether the portion of those costs which I could reasonably allocate to him - which would be an accounting hassle - are equal to, less than, or greater than the COA.
I'm not sure I understand your comment about camfused and gifting. I do think a lot of gifting goes on within families in all directions.
I agree with your last paragraph, and I have always said in addition to what you wrote, that I am willing to go into an audit, explain my position, have them tell me I'm wrong, learn from my mistake, and pay whatever penalties and interest they say to pay. I generally hope that if I have read the rules carefully, made an honest effort to apply them to my situation, and keep good records, I at least will not get thrown into prison.
I'll have to revisit my practices. Thanks for the response.