Boiler and Furnace Emission Rules for Factories

A factory boiler or furnace must be covered by the unit's consent under the Air Act, must burn only the fuel the consent allows, must have the air pollution control equipment and stack height the consent specifies, and must keep its emissions within the standards in the Environment (Protection) Rules 1986 and the consent order. The unit has to monitor its stack and keep records. If a board sample fails, expect a show-cause notice, directions to fix it, environmental compensation and, if nothing changes, closure.

This guide is written mainly for factory owners, plant managers and compliance staff: what the pollution rules expect of a boiler or furnace, how to stay on the right side of the board, and what to do when a stack test goes wrong. Residents will find it useful too, because knowing what a unit should have makes a complaint sharper; for that side, see how to complain about factory smoke.

For the overall picture of industrial emissions and how complaints and notices are handled, see our page on factory air pollution and stack emissions.

The essentials

What emission rules apply to a factory boiler?

Three layers apply. First, the Air (Prevention and Control of Pollution) Act 1981: a unit with a boiler or furnace needs consent to establish (CTE) before installation and consent to operate (CTO) before running, under section 21, and section 22 bars emissions beyond the standards. Second, the emission standards in the schedules to the Environment (Protection) Rules 1986, which include standards for boilers and furnaces and for specific industries that use them. Third, and in practice the most important, the unit's own consent order, which turns those general standards into specific conditions for your plant.

A consent order for a unit with a boiler typically states the boiler's capacity, the permitted fuel and its quantity, the air pollution control device to be installed, the stack height and diameter, the sampling port and platform, the frequency of stack monitoring, and the emission limit for particulate matter and, where relevant, gases such as sulphur dioxide. Inspectors check the plant against that document, line by line.

Boiler safety is a separate regime. Registration, inspection and certification of steam boilers are handled by the state's boiler inspectorate under the boiler law. A valid boiler certificate says the boiler is safe to operate; it says nothing about whether its emissions are lawful, and boards do not accept it as a substitute for consent.

Do I need fresh consent for a new boiler or furnace?

Usually yes. Adding a boiler, replacing it with a larger one, adding a furnace, or switching fuel changes the unit's emissions, and boards treat that as a change requiring an amendment or expansion of consent. Installing first and applying later is one of the most common reasons units end up with closure notices, because the inspection that follows a complaint finds equipment that the consent does not mention.

Advocate B.K. Singh's practical advice to units planning a new boiler is to file the consent amendment with the boiler's specification sheet, the fuel analysis and the design of the control device, and to wait for the amended consent before commissioning. The delay is real, but it is far shorter than the time a closure direction can cost, and a unit operating without valid consent also faces penalties and environmental compensation. Our pages on consent for expansion and penalties for running without consent to operate explain both sides.

The same applies on renewal. When the consent to operate comes up for renewal, the board compares what is installed with what was approved. A boiler upgraded quietly three years ago becomes a problem at renewal, so regularise it before then.

Common boilers and furnaces, their main pollutants and usual controls

The right control device depends on the fuel and the process. This table shows typical pairings; your consent order decides what your unit must have.

Which fuels can a factory boiler or furnace use?

Only the fuel named in the consent. That sounds obvious, but fuel substitution is the most common cause of black smoke complaints. When prices move, some units start mixing tyres, plastic waste, used oil or industrial sludge into the boiler. Burning hazardous or other waste as fuel is lawful only with specific authorisation under the Hazardous Waste Rules for an approved process, and an ordinary boiler does not qualify; see hazardous waste authorisation.

In Delhi NCR the rules are tighter. The Commission for Air Quality Management has notified a list of approved fuels for industries in the region and has directed a shift away from coal towards cleaner fuels such as piped natural gas and biomass. Fuels such as pet coke and furnace oil have long been restricted for industrial use in NCR. Units on unapproved fuel risk closure, and GRAP adds further restrictions during bad air episodes; see CAQM directions for NCR units and the GRAP stages.

Keep fuel purchase bills, delivery challans and a stock register. Inspectors look at the fuel yard, and a pile of shredded tyres next to a boiler permitted to burn husk tells its own story. Biomass is not a free pass either: husk and wood boilers produce heavy particulate loads and need working dust control.

What stack height and sampling arrangements are required?

The stack height for a boiler is set by the standards and written into the consent order. The EP Rules use formulas that relate minimum stack height to the boiler's capacity or its emission load, so that pollutants disperse before reaching ground level. Your consent will state a figure; build to that figure, not to what fits the shed roof. A stack lower than required is a straightforward violation, and it is also the cause of many residents' complaints, because a short stack drops smoke and ash straight onto neighbouring roofs.

The stack must also have a sampling port at the right height with a safe platform and ladder, so a laboratory can take an isokinetic sample. Units sometimes skip the platform, and the board then records that the stack could not be sampled, which is itself treated as non-compliance. Where online continuous emission monitoring is required, the analyser is fitted on the stack and connected to the board's server.

If you share a stack between a boiler and a thermic fluid heater, or between two furnaces, check that the consent permits it and that the stack is designed for the combined load.

Records and returns a unit with a boiler or furnace should keep

How to bring a boiler or furnace into compliance

If you are installing new equipment or cleaning up an existing plant, this order of work avoids most problems.

What happens if a boiler fails a stack test?

A failed board sample usually leads to a show-cause notice asking why action should not be taken under section 31A of the Air Act. The notice will cite the result and the standard, and often other findings from the inspection, such as missing logbooks or a bypass duct. After considering the reply, the board can direct the unit to install or upgrade equipment within a time, to stop the boiler, to close the unit, or to have its electricity or water disconnected.

Boards also levy environmental compensation using the CPCB's formula-based method, which looks at the unit's category and size, the duration of the violation and the location; our guide on what environmental compensation means explains it. Since the Jan Vishwas Act 2023, many violations of the Air Act also attract monetary penalties fixed by an adjudicating officer rather than prosecution.

The reply matters. Ask for the sampling record and the laboratory report under RTI if they were not attached, and check the load at which the sample was taken and whether the method was followed. But do not stop there. A reply that shows the fault has been found and fixed, with a fresh report from a recognised laboratory, is what usually leads to a direction being withdrawn or a closure being revoked, often with a bank guarantee. For help with the notice itself, see our page on replying to pollution board notices.

Rules for induction, cupola and reheating furnaces

Furnaces raise different problems from boilers. An induction furnace melting scrap releases its heaviest fumes during charging and tapping, not through a fixed chimney, so the key control is a hood or canopy that captures the fumes at the furnace mouth and ducts them to a bag filter. Inspectors look at whether the hood is in place, whether the extraction fan is running during melting, and whether fumes are escaping through the roof vents of the shed.

Cupola furnaces in foundries emit dense particulate and carbon monoxide and need a scrubber or bag filter, with an afterburner where the consent requires it. Reheating furnaces in rolling mills depend heavily on fuel: on gas they are relatively clean, on coal or oil they are not. Secondary sources, such as scrap yards, slag handling and coal or coke storage, cause much of the dust that neighbours notice.

The scrap itself is a compliance issue. Painted, oily or plastic-coated scrap produces smoke and smell when melted, and boards increasingly check the charge mix. Our guide on steel and rolling mill pollution covers that sector in detail, and kilns in brick-making are covered in brick kiln pollution rules.

Documents to keep ready for a board inspection

What residents can check about a factory boiler or furnace

You do not need to be an engineer to spot the signs. Thick black or brown smoke from a boiler chimney usually means poor combustion, the wrong fuel, or a dust collector that is not working. Flakes of black ash on terraces point to unburnt fuel escaping through a cyclone that is overloaded or a bag filter that is bypassed. A chimney that barely clears the shed roof is worth photographing, because stack height is written into the consent and is easy for an inspector to measure.

Watch the fuel too. Trucks unloading shredded tyres, plastic bales or drums of oil at a unit whose boiler is supposed to burn husk or gas are a strong lead. Note the dates and photograph from a public place. Smoke that appears mainly at night, or on Sundays, often means the control equipment is being switched off when the owner thinks nobody is checking.

Use this in your complaint. Ask the board under RTI for the unit's consent order, which states the permitted fuel, the control device and the stack height, and then ask for an inspection that checks each of them, with a stack sample. A complaint that says 'the consent requires a bag filter, but the smoke at night suggests it is not running' is far harder to brush aside than a general complaint about pollution.

Is your boiler or furnace compliant?

Related guides

Diesel generator sets have their own emission and noise rules; see DG set rules in Delhi NCR. For the consent to operate itself, including renewals and documents, see our page on consent to operate.