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(Lessons from our 25kW log burner installation on Marcus’ off-grid home).
In this case study, we will discuss how a Grand Designs-featured woodland cabin achieves near-zero energy heating using one of our 25kW log burners and a 1,500-litre thermal store.
Hear directly from Marcus (the property owner) on his YouTube channel, Big Wood Cabin.
It was a pleasure to work with him.
Featured on Grand Designs, the Big Wood Cabin sits within 22 acres of English woodland and was built almost entirely from timber felled on the owners' own land. The challenge was not simply to heat the home, but to do so sustainably: without a mains gas connection, without draining a solar battery bank, and to a Passive House standard of insulation. The solution was a wood-fired heating system engineered around one central principle: fire once, stay warm for days.
A 25 kW log burner, housed in a dedicated boiler shed, provides all the heat this home needs. Fuelled by ash and oak from the owners' own land, it is a genuinely closed-loop system.
The critical detail for off-grid buyers: this model requires no electricity to operate. No fans, no pumps, no draw on the battery bank. In winter, when solar generation is lowest and heating demand is highest, this fail-safe is invaluable.
Shop our log gasification boilers today.
The buffer tank is the component that makes this system genuinely practical. Once heated to 90°C, the 1,500-litre thermal store holds enough energy to supply hot water for showers and baths for almost a week with no need to relight the fire.
Two internal stainless steel coils handle heat distribution: one to the domestic hot water circuit, one to the space heating circuit. The result is steady, reliable warmth delivered long after the flames have died down.
Heat travels from the boiler shed to the cabin via a 25-metre underground insulated pipe run, then passes through a 7 kW heat exchanger into the home's MVHR (Mechanical Ventilation with Heat Recovery) system which effectively turns the ventilation infrastructure into a gentle whole-house radiator.
In summer, an immersion heater powered by surplus solar energy takes over hot water duties entirely, keeping the system useful year-round without touching stored battery power.
Shop buffer tanks and thermal stores today.
…The heating system was near perfect, just a few more radiators needed
The MVHR alone was not quite sufficient to heat every room comfortably on the coldest days. Bedrooms and corridors (further away from the unit and more exposed) needed a boost.
The fix was simple: radiators and heated towel rails added to cooler areas, all fed directly from the buffer tank circuit. It is a refinement worth planning for at the design stage rather than retro-fitting later.
Get in touch with us at The Biomass Hut for sustainable heating solutions for your new home.
Use Our Bespoke Tank Designer — Size Your System Online
Download the Buffer Tank Sizing Guide — Why Volume Matters
Utilise UK Government incentives for heating your home