# Boilers, furnaces and stoves: Engineering methods

From 100 MW steam boilers to three stones under a pot

Source page: https://www.materialinsights.org/energy/e_combustion_heat/methods/

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 systems**^[3](https://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/steam15_benchmark.pdf) | 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 kilns**^[2](https://www.energy.gov/sites/prod/files/2016/06/f32/QTR2015-6I-Process-Heating.pdf) | 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)**^[4](https://www.energy.gov/node/374305)^[12](https://heatpumpingtechnologies.org/articles/heat-pumps-step-up-what-the-ieas-heat-pump-monitor-2026-means-for-heating-industry-and-energy-security/) | 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 stoves**^[6](https://link.springer.com/article/10.1007/s43937-024-00055-3)^[11](https://www.businesswire.com/news/home/20240514007401/en/TotalEnergies-Takes-Action-to-Give-Access-to-Clean-Cooking-to-100-Million-People-in-Africa-and-India)^[13](https://cleancooking.org/news/10-16-2018-voluntary-performance-targets/) | 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 cookstoves**^[5](https://www.iea.org/reports/clean-cooking-in-africa-2026/executive-summary)^[6](https://link.springer.com/article/10.1007/s43937-024-00055-3)^[13](https://cleancooking.org/news/10-16-2018-voluntary-performance-targets/) | 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

1. [Quadrennial Technology Review 2015, Chapter 6 Technology Assessment 6I: Process Heating](https://www.energy.gov/sites/prod/files/2016/06/f32/QTR2015-6I-Process-Heating.pdf) US Department of Energy, 2015
2. [Benchmark the Fuel Cost of Steam Generation, Steam Tip Sheet #15 (DOE/GO-102012-3391)](https://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/steam15_benchmark.pdf) US Department of Energy, Advanced Manufacturing Office, 2012
3. [Furnaces and Boilers](https://www.energy.gov/node/374305) US Department of Energy, Energy Saver, 2025
4. [Clean Cooking in Africa 2026: Executive summary](https://www.iea.org/reports/clean-cooking-in-africa-2026/executive-summary) International Energy Agency, 2026
5. [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)](https://link.springer.com/article/10.1007/s43937-024-00055-3) Springer Nature, 2024
6. [TotalEnergies Takes Action to Give Access to Clean Cooking to 100 Million People in Africa and India](https://www.businesswire.com/news/home/20240514007401/en/TotalEnergies-Takes-Action-to-Give-Access-to-Clean-Cooking-to-100-Million-People-in-Africa-and-India) TotalEnergies via Business Wire, 2024
7. [Heat Pumps Step Up: What the IEA's Heat Pump Monitor 2026 Means for Heating, Industry and Energy Security](https://heatpumpingtechnologies.org/articles/heat-pumps-step-up-what-the-ieas-heat-pump-monitor-2026-means-for-heating-industry-and-energy-security/) IEA Heat Pumping Technologies TCP, 2026
8. [Voluntary Performance Targets for cookstoves (ISO 2018 tiers)](https://cleancooking.org/news/10-16-2018-voluntary-performance-targets/) Clean Cooking Alliance, 2018

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_combustion_heat/index.md)
- [Overview](https://www.materialinsights.org/energy/e_combustion_heat/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_combustion_heat/correlation/index.md)
- [Science and limits](https://www.materialinsights.org/energy/e_combustion_heat/science/index.md)
- [Value chain](https://www.materialinsights.org/energy/e_combustion_heat/valuechain/index.md)
- [Unit economics](https://www.materialinsights.org/energy/e_combustion_heat/economics/index.md)
- [Equipment and suppliers](https://www.materialinsights.org/energy/e_combustion_heat/equipment/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_combustion_heat/links/index.md)