If they do remove the furnace, you should not expect to get one dime of your money back.
Out of that $3,000 you would deduct the cost of the original install and then the removal of the furnace and capping off the line or pluming the line to keep your water on.
And then if you want the furnace back and installed, you would have to pay them all over again so don't expect to have any money left out of the $3,000 to use as a down payment.

