what tax burden are you thinking he is going to be relived of?

Technically, he should be charging you an interest rate that reflects the market, otherwise, it runs afoul of other IRS rules.  1.5% would be reasonable for three years in today's market. 

then that interest is taxable income to him but not deductible to you unless it is collateralized by real estate.

@brent3  , agreeing with @NCperson , if this is a formal loan . he either has to charge a market rate  for this type of loan or be subject to imputed interest earnings.

On the other hand if this is personal and informal loan ( word of mouth ) and therefore  not enforceable  as far as return of the monies are concerned ), then there is no reporting  and nothing happens-- not a tax event. Generally  most , would opt for a written and formal document ( to ensure pay back and not being treated as a gift ) and therefore market interest rate needs to be  shown as income.