With the price of oil these days ($4 per gallon), you don't want to be burning a lot.
We are using 1/2 gallon a day and it's costing us $2 a day (at today's prices).
If you have tons of wood and tons of time to chop it, adding an outdoor HX sounds good.
(My oil burner can also use solid fuel).
You could leave the oil burner operational as a back-up. (Peace of mind).
You could put one of these
Wood boiler heating systems intelligently engineered by Tarm Biomass » HS Tarm Solo Innova »
in your basement, and forget the outdoor boiler.
Adding a big storage tank may allow you to pre-heat the water when you have some spare time..
Or, if you can seal up the house and add insulation, your area should be ASHP friendly. (Think
Inverter Mini-Split).
http://meetoncruise.com/ports/images/vancouver_temp.jpg