One of the challenges with
wood heat is that it is difficult to get an efficient burn while modulating the amount of heat output. This is why people like high thermal mass heating devices such as masonry or
rocket mass heaters. With boilers like this, the best way to add thermal mass is to install an super-insulated thermal storage tank. The thank is filled with water. The boiler gets fired any time the water in the tank drops below a certain temperature. The boiler is run at full (maximum efficiency) until the tank heats up. The heating systems then use the heat from the thermal storage tank. One of the advantages to a system like this, is that heat can be drawn off the thermal storage thank for any number of uses, included domestic hot water.
Where I live, we use a Garn boiler, which is a wood fired boiler with ~2,000 gallons of integrated water thermal storage. This boiler provides all our building and domestic hot water needs. It will also be the heat source for a hot tub at some point in the future.
There are two ways to increase the thermal storage capacity of a water tank:
1. Install a bigger tank
2. Allow a larger difference in high and low temperatures. In order to do this, you need to be able to extract heat at a low temperature. Radiant floors are a good way to do this. In a well insulated building, a polished
concrete floor can heat a residence with only 95 F supply water temperature. Baseboards typically require at least 140 F supply temperature. It looks like you already have this
project under construction. If radiant flooring is not an option, consider using hydronic baseboard with high surface area designed for low temperature water supply. If you are able to heat your house with water at 110 F, you might only need to fire the boiler
enough to heat a 2,000 gallon tank to 180 F once every four days, even in the middle of the winter, depending on where you live.