Boilers, furnaces and stoves: Engineering methods

From 100 MW steam boilers to three stones under a pot

What this tab covers The engineering methods that can do this conversion, compared on efficiency, scale, economics, limitations and reliability.

Methods range from 100 MW-class industrial steam boilers to three stones under a pot. All share the same physics; they differ in temperature, control and how much flue heat they recover.

Comparison

Method	Efficiency	Scale	Economics	Limitations	Reliability
Industrial boilers and steam systems³	Combustion efficiency 86 to 90% with heat recovery (DOE benchmarks)	Small packaged units to large water-tube boilers	Fuel dominates; steam about 4 to 9 USD per 1,000 lb at 3.5 to 8 USD/MMBtu gas (calculated)	Distribution losses, failed steam traps and uninsulated pipes can waste much of the output	Long-lived pressure vessels; fouling and scale on tubes, corrosion and tube leaks are common failure modes
Furnaces and kilns²	Falls with temperature as hot exhaust and, above about 540 C, radiation losses grow	Up to the largest industrial units	Fuel-dominated; recuperators and regenerative burners cut fuel use	Hardest to electrify: calcining 1,500 to 2,000 F (about 820 to 1,090 C) and melting up to 3,000 F (about 1,650 C)	Refractory wear sets rebuild cycles
Gas boilers (homes and buildings)⁴¹²	90 to 98.5% AFUE condensing	Homes and commercial buildings	Cheapest heating system to buy in most markets; heat pumps cost 2 to 4 times as much	Locks in gas use and CO2	Condensate drains, ignition and fan faults
LPG and natural gas stoves⁶¹¹¹³	About 42 to 70% (World Bank estimates); ISO lab tests rank stoves from Tier 0 (below 10%) to Tier 5 (50% or more)	Household and commercial kitchens	Cylinder deposit and refill cost are the barriers; pay-as-you-cook meters spread payment	Depends on import and storage logistics	Hoses and regulators are the main safety parts
Biomass cookstoves⁵⁶¹³	Open fires and the simplest stoves: Tier 0 in ISO lab tests (below 10%); improved stoves aim for Tier 2 to 4 (20 to 40% or more); traditional injera baking stoves only 5 to 10% (World Bank estimate)	Household	Fuel often gathered rather than bought; improved stoves funded partly by carbon finance	Household air pollution from lack of clean cooking contributes to about 2.5 million premature deaths a year worldwide	Durability of cheap stoves is a recurring problem

Industrial boilers and condensing gas boilers convert fuel to heat at 85 to 98% efficiency, so the energy losses are small; the waste is in exergy, because a flame is used to make low-temperature heat. Furnaces and kilns are less efficient but serve temperatures heat pumps cannot reach. Cooking spans the widest range, from below 10% for open fires to around 70% for the best LPG stoves, with health effects that matter more than efficiency.

How each method works

Industrial boilers and steam systems

Fire-tube boilers pass hot gas through tubes inside a water-filled shell; water-tube boilers put water inside tubes surrounded by flame, which suits higher pressures. Steam is piped to process users and condensate returned.

Furnaces and kilns

Fuel burns directly in a lined chamber to heat metal, glass, ceramics or cement raw meal for drying, calcining, melting or heat treating.

Gas boilers (homes and buildings)

A fan-assisted burner heats water for radiators and taps; condensing types add a second heat exchanger to recover latent heat from the exhaust.

LPG and natural gas stoves

A burner mixes gas and air under the pot; LPG comes in refillable cylinders.

Biomass cookstoves

Three-stone fires, improved stoves with insulated combustion chambers, and fan or gasifier stoves that burn wood gas more cleanly.

Sources

Quadrennial Technology Review 2015, Chapter 6 Technology Assessment 6I: Process Heating US Department of Energy, 2015
Benchmark the Fuel Cost of Steam Generation, Steam Tip Sheet #15 (DOE/GO-102012-3391) US Department of Energy, Advanced Manufacturing Office, 2012
Furnaces and Boilers US Department of Energy, Energy Saver, 2025
Clean Cooking in Africa 2026: Executive summary International Energy Agency, 2026
Design and experimental investigation of an LPG injera baking stove for sustainable energy use in Ethiopia (Abdella, Alemu and Dino), Discover Energy 4, 32 (quotes World Bank stove efficiency estimates) Springer Nature, 2024
TotalEnergies Takes Action to Give Access to Clean Cooking to 100 Million People in Africa and India TotalEnergies via Business Wire, 2024
Heat Pumps Step Up: What the IEA's Heat Pump Monitor 2026 Means for Heating, Industry and Energy Security IEA Heat Pumping Technologies TCP, 2026
Voluntary Performance Targets for cookstoves (ISO 2018 tiers) Clean Cooking Alliance, 2018