i use to use a gas engine attached by belt to a truck alternator to charge my battery bank (36 volt golf car with custom built wires and anderson connectors to quickly change from 36 volt to 12 volt and back again) that was a mobile battery bank, also had a solar panel on its roof.
back to the gas engine part. i had a stainless steel pot with a hole in the side with some broken fire brick inside to hold another stainless steel pot above the hole inside the first pot . the outside pot sat on a concrete block to give it the correct height to run a piece of pipe from the exhaust pipe (the muffler had a small pipe exiting the gases)
this allowed me to heat water in the inner pot (with a stainless steel lid) with the waste heat from the engines exhaust! we lived in a camper in rural south dakota for 3 straight years. minus 30F temps.
we used a M1950 (extreme tent heater) surplus wood stove to heat the 2000 year model 31 foot long camper with a 12 foot slide out. the stove is a real piece of crap but will burn not only wood, but also gasoline fed from a jerry can. i never used anything but wood in it. i went through 2 grates in just 1 winter burning the maple flooring i scrapped/salvaged from the old house on the property that needed burning down because of the raccoons living in it. the lack of air tightness would cause the thermometer on the wall of the bedroom (at opposite end of the trailer) to reach 105F around 2am with -30F temps outside. i would throw both doors open to cool the trailer down, even in a blizzard!!
engineer775 has an old video on youtube about endless hot water. if i remember correctly it uses a rocket stove to heat water in a copper coil . cold water in and steaming hot water out! and it also used a hot water tank for the storage of the hot water.
i also use to buy 35 yard dumpsters of lumber scraps and sawdust mixed from a garbage hauler that got it from a TRUSS FACTORY, i think i paid around $185 for it with delivery. lots of 2x materials even up to 3 foot long. i used a screen made from chicken wire at an angle to remove the small pieces of wood from the saw dust, would store these in plastic bags i got from a neighbor (wood pellet bags) and burn the small stuff in the M1950 , just throwing the chips in by hand, leaving the lumber for when my wife was feeding the stove. a person could actually lay the lumber scraps flat and nail/screw them down to build a house with 3 1/2 inch thick solid wood walls (article about this in an old mother earth news magazine. i got 3 foot long 2x12 in those dumpsters too.
thought this info might give you some ideas on heating allerton abby with hot water. if a person were to put hot water lines in the soil battery portion when constructing the wafati using big rolls of PEX pipe, the heat battery could be charged even with a solar water heater using thermo siphon to pump the hot water to the top and gravity flow back to the heater, to charge it during the summer months.
the university of iowa published a 8 1/2 x 11 paper back book in the 1970s with ways actual old farmers were getting free heat and electricity etc.. one dug a big hole where his shop was going to be and filled it with large rocks, then built his shop on top, on a slab. he built a solar air heater and used a fan to blow the heated air down to heat those big rocks , then in winter they heated his shop by circulating air around those rocks and blowing it into the shop
another used old iron edison batteries from a train and a wind generator for his electricity , he was in his 80's and HAD NEVER HOOKED TO THE GRID IN HIS 80 SOMETHING YEARS!! lots of good ideas in it that actually worked and low cost DIY
