Break even calculation.

220K at 3.75% x 30 years => monthly payment = 1019

220K at 4.5% x 30 years => monthly payment = 1,115

(1115-1019) = $ 96 saving a month. 

$2400 / $96 = 25 month to break even. 

So if you plan to keep the mortgage for 25 months or more, take the 3.75%.