Yes, it will affect your 2014 tax refund if you get married. You won't get any EIC. You can't claim EIC if you file MFJ because your joint income is too high. You can't claim EIC if you file MFS either - it's NOT allowed. The refundable additional child tax credit you are accustomed to receiving if your children are under age 17, will be used to reduce your joint tax debt.
EIC on 34 k using 2013 EIC table whether filing single or head of household if you qualify - 2,570 EIC & may increase up to $99 more in 2014. You lose this if you get married. (Bostonian is using EIC figures for a married couple filing joint at your income level of 34k)
Usually MFJ is more ben