Heating for an addition

We are looking into building a master bedroom and bath addition onto a 1,900+ sq. ft. house with hot water heat (oil fired). We will be doing most of the work ourselves over time. The addition will be about 500 sq. ft. and we intend to put it over a crawl space. Other than extending the current system, which would seem to be expensive (would it compared to a separate system?) to do and the current boiler may not be sized to handle the extra load (or does that matter?), what might be reasonable options for heating (in a rural area with no natural gas available)? We sized the A/C unit recently added to account for an addition so we are good on that aspect. Thanks for any suggestions!