Skip to content
Wood boiler sizing starts with square footage, but the right model depends on more than that — your family choice (PRO, UNI, TITAN Lambda, or UNI Industrial), fuel preference, and how automated you want the system to be all shape the final decision.
This guide walks through BTU basics, the full sizing table across MBTEK's wood boiler lineup, which family actually fits your project, and what to check before you buy.
BTU basics: how wood boiler sizing works
Wood boiler sizing is based on BTU per hour — the heating capacity needed to keep the building comfortable at your coldest expected outdoor temperature. Square footage is a useful starting point, but it isn't the final answer.
The real number depends on:
- Climate and winter design temperature for your location.
- Insulation and air sealing — a leaky or poorly insulated building loses heat faster and needs more capacity.
- Hydronic distribution — radiant floors, radiators, and fan coils each place different demands on the system.
- Domestic hot water — if the boiler will also supply DHW, that load needs to be added to the sizing conversation.
Read how a wood boiler works first if you want the mechanism explained before comparing models.
Size by square footage: family and model table
MBTEK's wood boiler lineup spans four families, each built around a different priority. Before comparing exact models, here's the fastest way to tell them apart:
- PRO — simplest and lowest cost: no electricity required, and the only family that also burns coal or briquettes. Best for off-grid cabins, small homes, and shops.
- UNI — best all-around value: 86%+ efficiency with a standard smart controller. MBTEK's featured recommendation for most wood boiler projects.
- TITAN Lambda — highest efficiency, most automated: up to 95% efficiency with automatic ignition and oxygen-sensor lambda control. Costs more than UNI, pays back in fuel savings and less manual burn-tuning.
Each model below links to its product page — use this as a starting range, not a final answer:
This covers residential and light-commercial projects up to 8,000 ft². Heating a farm, workshop, or commercial building beyond that range? MBTEK's UNI Industrial family includes models with approximate heating areas up to 12,000, 17,000, and 24,000 ft²; UNI 1000 requires project-specific sizing. Approximate coverage only. Final selection requires a building heat-loss calculation and MBTEK sizing review. See the family comparison below or browse UNI Industrial wood boilers.
These ranges are approximate — final sizing depends on heat loss, insulation, climate, buffer tank design, and chimney planning. See how much a wood boiler costs for equipment pricing by model, and confirm final sizing with an MBTEK specialist before ordering.
Which wood boiler family fits your project
Family matters as much as size. Each MBTEK wood boiler family targets a different combination of power needs, fuel flexibility, and automation:
PRO
- Power requirement
- None — runs fully off-grid.
- Fuel flexibility
- Wood, coal, or briquettes — the only family that burns anything besides wood.
- Efficiency
- 86%.
- Best fit
- Off-grid cabins, small homes, shops, or the simplest, lowest-cost option.
UNI
- Power requirement
- Standard electrical service.
- Fuel flexibility
- Wood only.
- Efficiency
- 86%+.
- Best fit
- Most wood boiler projects — MBTEK's featured, best-value recommendation.
TITAN Lambda
- Power requirement
- Standard electrical service.
- Fuel flexibility
- Wood only.
- Efficiency
- Up to 95%.
- Best fit
- Maximum efficiency and automation — automatic ignition and lambda combustion control.
UNI Industrial
- Power requirement
- Standard electrical service.
- Fuel flexibility
- Wood only.
- Efficiency
- 86%+.
- Best fit
- Farms, large workshops, commercial buildings, and loads beyond UNI's largest model.
If you're weighing whether a wood boiler is worth it against other heating options, the honest answer depends on which of these fits your situation: PRO for off-grid independence, UNI for the best all-around value, TITAN Lambda for maximum efficiency and automation, or UNI Industrial for scale.
Fuel flexibility: coal, pine, and other wood types
Only PRO can burn coal or briquettes alongside wood — UNI, TITAN Lambda, and UNI Industrial are wood-only. If fuel flexibility beyond firewood matters to your project, PRO is the only family that qualifies.
Softwoods like pine can be burned in any wood boiler, but they burn faster and produce more creosote and resin buildup than hardwoods, so a system running mostly softwood needs more frequent chimney cleaning and closer attention to burn temperature. Well-seasoned wood — properly dried, regardless of species — matters more for clean, efficient combustion than the specific species you burn.
Indoor installation and siting
Setback distance from the house is a real planning question for an outdoor wood furnace — many jurisdictions regulate how far an outdoor unit must sit from neighboring structures because of smoke. MBTEK's wood boilers are indoor units, so that specific concern mostly doesn't apply: the boiler installs inside a mechanical room, basement, or utility space, connected directly to the hydronic system. See indoor vs outdoor wood boilers for the full comparison.
What does matter for an indoor installation is chimney clearance, combustion air supply, and local code compliance — those requirements come from your specific model's installation manual and local building code, not a single number that applies everywhere. Confirm exact clearances with an MBTEK specialist or your installer before finalizing mechanical room layout.
MBTEK recommendation
Match the family to your situation, then size the model
Start with the family decision — off-grid or fuel flexibility points to PRO, most projects are best served by UNI, maximum efficiency and automation points to TITAN Lambda, and large-scale heating needs point to UNI Industrial. Once the family is set, match BTU output to your heat load using the sizing table above.
- Browse the lineup: See all four families at MBTEK wood boilers.
- Check pricing: Read how much a wood boiler costs for current equipment prices.
- Confirm sizing: Use the System Builder or contact MBTEK before ordering.
Buying checklist before choosing wood boiler size
Before choosing a wood boiler size and family, confirm these points:
- What is your approximate square footage and heat loss?
- Do you need off-grid operation or fuel flexibility beyond wood?
- Do you want the simplest manual system or the most automated option?
- What hydronic distribution will the boiler feed?
- Do you have a usable chimney, or does one need to be planned?
- Who will size, install, and service the system?
Size by family first, then by BTU
Wood boiler sizing isn't just a square-footage lookup — the family you choose (PRO, UNI, TITAN Lambda, or UNI Industrial) shapes fuel flexibility, automation, and efficiency just as much as the BTU output does.
Start with what your project actually needs — off-grid capability, fuel flexibility, automation, or scale — then match the model using the sizing table above, and confirm with a specialist before you order.
