On the inland waters of WA & BC it's ALL shoulder-season. Mark Twain made some remark about the pleasantest winter he ever experienced was one summer he spent on Puget Sound. The aforementioned cold -7C day (about +20F) would be considered a pretty balmy January day in Winnepeg- practically T-shirt weather. It gets down to -15C/+5F there once per decade or so, but never for long enough to matter. The average winter temp is well above freezing.
In Seattle-Tacoma / Vancouver-Nanaimo-Victoria many of the better mini-splits will deliver an annual average COP efficiency of 3.5-4.0, usually beating the labeled HSPF efficiency. Right-sized mini-splits run continuously at their lowest blower speed most of the time, and would be quieter than most refrigerators. They are in NO way comparable to the hot blast noise & cycling of the typical 5x oversized propane hot air furnace. It's like night & oranges- not even on the same axis.
dmaceld's "mini-split in the conditioned crawlspace" approach to radiant floors would work even better at the mild outdoor temps of southern Vancouver Island than at dmaceld's much colder Idaho location, if you opted for a crawlspace approach rather than slab-on-grade foundation. It's described briefly (if not clearly) in this thread:
http://www.greenbuildingtalk.com/Forums/tabid/53/aff/21/aft/83461/afv/topic/Default.aspx
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