Well yes and no! Or it depends, right? A friend actually approached me with that very question. He has a two-story, open architecture, house, actually three-story given the basement shop, all heated with wood. (Biomass these days, right?) Here, there might be two right answers. If installed to supplement the wood stove then, yes the mini-split could work well. But if it is to be the main heating system, maybe not.
First of all, what is a Mini-split? It is a heatpump for sure. One might call it an air to radiant. Generally on the smaller side with the outdoor air unit and the indoor radiant unit or “head”. Sometimes there might be several heads, but that’s the basic unit. While there can be air flow across the inner head, there is no ducting so heat is very localized.
Efficiencies can be good in cooler weather to not so good in cold weather. In cold weather there are two things acting against it. There is not so much heat in the air and the indoor unit is calling for more heat and therefore higher temperatures both pushing down the efficiency.
Generally there is not a backup heating element as we have in the air-air and air-water so sizing the unit for worst case conditions is difficult. But if a house been designed with a mini-split in mind, with an open house layout and with low heating loads, it can work. To the mini-split’s credit, most have variable speed refrigerant compressors so that over sizing is not a major issue in efficiency, just cost. With the mini-split, the main issue I see is the inability to direct the heat where you might want it, say the bathroom. And I find the “head” mounted on the wall less than attractive.
Back to our friends. They installed the mini-split and are very pleased with it, using it in the fall and spring to knock off the morning chill in the kitchen while having coffee. They might not even start the woodstove on days when the sun is out. Even mention a savings of some fire wood for not much in electrical useage.
The mini-split also served another purpose. It replaced a build-in electric heater wall heater that was used to keep the house from freeze up if gone in the winter. While the mini-split may not maintain temperature in winter, it can keep the house above freezing in our climate.
Bottom line, the mini-split can add value by recognizing its limits and designing accordingly.