I am looking for advice on equipment needed and procedure for tying my hot tub into my heating system. I have a wood fired outside boiler that is looped into a plate heat exchanger. The original boiler for my house is looped through the other side of the heat exchanger, therefore providing all of the hot water for the baseboard heat and hot water. The original boiler still functions as the hot water tank and still circulates the hot water to the baseboard heat zones. Only difference is I don't have to buy oil. This is very efficient, only losing a couple degrees from the 180 degree water coming from the boiler.  I would like to hook my hot tub into this system somehow. I have a standard hot tub which is right outside my house which is no more than 30 feet from my inside boiler, heat exchanger etc.

I would like to avoid some of the increased use of electricity that is used by the spa heater to maintain the 100-105 F degree water temp. 

I also have an extra heat exchanger ( 10 plate ) I thought maybe I could loop that into the house boiler and loop the hot tub into the other side with a 3 way automatic valve and could either tie that into the hot tub thermostat ( if possible) or have an external thermostat.

Obviously I am looking to find the least expensive way with the least amount of work.