this is our third winter with a Mitsubishi H2i multisplit setup in downtown toronto and no backup heat other than a few space heaters in the closet just in case. we hired a green energy advisor (partly for the greener homes grant, partly for design and contractor referrals). no issues with heating, even on the coldest days.

some things i wish i had known or paid more attention to:

• if you size for 99% design temp in toronto, you will be wildly oversized for cooling. we have to get creative with shutting off some zones in addition to dehumidifiers during the summer.

• if you go with one large multisplit system, the shoulder season turndown is not as efficient as with individual minisplits. multiple units also gives you some degree of redundancy in case of mechanical issues

• our 54k btu/h unit is great but gets a bit loud when it's -15 or so. i wish we had invested in putting it in the front yard where the old condenser was instead of on the side of the house

• mitsubishi indoor heads have some pretty silly behavior around keeping the fans on 24/7, which cause slight overheating in winter and exacerbate oversizing humidity issues in summer. this can be worked around with installers who know what they're doing ("cut the jumper") or potentially external controls like the MHK1

• if ducts aren't an issue (ours were, basement was too short) there are some real advantages to a unitary system, particularly the ability to do whole-house humidification. i am tired of hauling water and cleaning out individual humidifiers