When my wife and I bought our first rectangle cabin of a whopping 320 sq. ft. (before kids, obviously) there was grid power available and thus for the first summer and fall an electric 120v plug in oil radiator heater was fine to keep the place livable. We were off the ground on sono-tubes and had 2×6 walls with 2×8 ceiling I believe, with fiberglass insulation and lots of windows. When winter set in we needed something stronger for heat- and we had built a wanigan for a whopping 384 sq.ft.!
We started looking at boat stoves. My wife recalled the oil drip heater on her family’s boat and the occasional belch of exhaust back draft in rough waters. We knew whatever we ended up with we would need to vent it, so a propane catalytic heater or Coleman stove with heat drum wasn’t going to work for us. With internet just coming out to the Big Lake area at the time, we got a few phone numbers to the known boat stove companies down in the Pacific Northwest. We had looked into Toyostoves, but understood that with a small cabin as such, the stove would probably turn on and off quite frequently as efficient as they are, and carbon build up would occur. We had a lot of birch from clearing our land but wanted continual fuel rather than worrying about cordwood loading. (In the end, we ended up buying a Perfection-Schwank oil drip heater (the 3 foot high, dark brown enamel ones that load the interior cabins for heat) from Sampson’s for ~$380 in Fairbanks and had it trucked down. It ended up being overkill and while almost always set on 1 of 6 gradients we had to open windows on the shoulder seasons).
For a dry cabin 500 sq. ft. or less, boat stoves are a great alternative and there are several styles readily available online. Some are oil drip style, and though they are about a quarter the size of the dark brown enamel Perfections, they are spendy- usually over $1000 (though one of the big box stores has a premiere brand at the moment for just over $800). Other options include propane models for ~ $600 and for the same price range a heater utilizing the antifreeze coolant off the boat engines (obviously not a helpful choice for a dry land cabin). Electric heaters are available yet they usually are 220 volts and something you would probably hook up straight to the breaker box. Charcoal fueled, vented samovars are available for minimal heat and with bio-bricks available this may be a viable option. Lastly, there are cooking units that have one burner electric (220v) and one burner alcohol; a stainless steel lid slides over the top and possibly such a unit could be adapter. Please let me know of other alternatives you have seen to warm micro-houses, dry cabins, or maybe even the famed mother-in-law apartments!