Short answer: an industrial boiler is chosen by the working medium the process needs (steam, hot water, warm water or thermal oil), then by the type of construction (shell boiler to EN 12953 or water-tube boiler to EN 12952), the available fuel, the actual load profile and the standards of the market where the plant will operate.
1. Which medium does your process really need?
The first question is not "how big a boiler" but "what should the boiler produce".
- Steam — for process applications (sterilisation, cooking, drying, reactors), turbines and cogeneration. Saturated steam covers most processes; superheated steam is needed for turbines and higher-temperature processes.
- Hot water (above 110 °C) — for district heating, large networks and industrial systems that move a lot of heat over distance.
- Warm water (up to 110 °C) — for building heating, domestic hot water and light industry.
- Thermal oil — when the process needs high temperatures without high pressure (asphalt, chemicals, wood processing, frying, drying).
The wrong medium is the most expensive mistake: a steam boiler for needs a warm water boiler would cover means higher investment, more demanding water treatment and stricter regulations with no real benefit.
2. Shell or water-tube boiler?
A shell (fire-tube) boiler has a large water content. Advantages: simpler construction, lower price, stable operation under varying load, easier maintenance. Limits: capacity and pressure. Built to EN 12953.
A water-tube boiler has a small water content; the water circulates through tubes that form the furnace walls. Advantages: large capacities, high pressures and temperatures, fast response, superheated steam for turbines. Built to EN 12952.
Rule of thumb: small and medium capacities and saturated steam — shell boiler; power generation, cogeneration, large capacities and superheated steam — water-tube boiler.
3. Which fuel is available, and at what price?
The fuel dictates the furnace design and, over the long term, an operating cost that exceeds the price of the boiler many times over.
- Natural gas — simplest operation, least maintenance, low emissions; dependence on gas prices.
- Liquid fuels (light and heavy fuel oil) — back-up or main fuel where there is no gas; heavy fuel oil needs preheating.
- Biomass (chips, pellets, straw, husks) — renewable and often the cheapest fuel, especially as a by-product; needs a grate, feeding, de-ashing and flue gas cleaning.
- Coal — still present in power generation; stricter environmental requirements.
- Electricity — no combustion, chimney or emissions; suited to smaller capacities, pharmaceuticals, laboratories and sites with cheap power.
- Waste heat — a waste heat recovery boiler produces steam from the flue gases of engines, turbines or furnaces, with no fuel.
Good practice is to design the furnace for two fuels (e.g. gas and fuel oil, or biomass and coal) where security of supply is critical.
4. How to size the capacity
A boiler is not sized for maximum consumption but for the actual load profile: how long the peak lasts, what the average is, and the technical minimum at which the boiler must run stably.
- An oversized boiler cycles, burns more fuel and wears faster.
- An undersized boiler cannot keep up with production and has no reserve for growth.
- Two smaller boilers instead of one large one often give better reliability: one runs, the other is standby, or they alternate.
The calculation needs: medium consumption per hour (peak and average), pressure and temperature at the consumers, return water or condensate temperature, operating regime (shifts, season) and expansion plans.
5. Which standards and certificates apply?
The boiler must be designed, manufactured and tested to the standard of the market where it operates:
- EN 12952 — water-tube boilers
- EN 12953 — shell boilers
- EN 13445 — pressure vessels; EN 13480 — industrial piping
- PED 2014/68/EU and CE marking — mandatory for the EU market
- ASME BPVC — the American code, required in the Middle East, Asia and Africa
- AD 2000 — German pressure equipment rules
Alongside the standards come the manufacturer's certificates: ISO 9001 (quality), ISO 3834-2 (welding), EN 1090 (steel structures), ISO 14001 and 45001 (environment and safety).
6. What else drives the total cost
- Water treatment — softening, deaeration and feedwater control protect the boiler from scale and corrosion.
- Heat recovery — an economiser and air heater raise efficiency and pay back within a few years.
- Automation — combustion, level and pressure control cut consumption and the need for constant supervision.
- Auxiliary equipment — tanks, headers, chimney, flue gas cleaning; simplest when the same manufacturer supplies them.
- Service — availability of spare parts and an overhaul team throughout the plant's life.
Checklist for your inquiry
- Medium: steam (saturated/superheated), hot water, warm water or thermal oil
- Consumption: peak, average and minimum (t/h, MW)
- Pressure and temperature at the consumers
- Fuel: type, availability, price, back-up fuel
- Operating regime: hours per year, shifts, seasonality
- Site: space, access, existing infrastructure, emission regulations
- Market and standards: EU (PED), ASME, AD 2000
- Expansion plans for the next 5–10 years
With this data our engineering team prepares a thermal calculation and proposes the boiler type, size and configuration. Since 1979 TIPO Kotlogradnja has designed and manufactured steam, hot water, warm water and thermal oil boilers, biomass boilers and auxiliary equipment, with more than 730 completed projects in over 15 countries.