GCV tells you only part of how coal will behave in your kiln. This guide walks through every line of a coal test report — moisture, ash, volatile matter, fixed carbon, sulphur, ash fusion and size — what each means inside a brick kiln, and the red flags to check before you buy.
In this article · 5 sections
Don't buy coal on GCV alone
The number sellers talk about most, GCV, tells you only part of how coal will behave in your kiln. GCV (gross calorific value) measures how much heat a kilogram of coal can give off under lab conditions. It says nothing about how fast the coal catches fire, how much of it is left behind as ash, or whether it will form clinker and stick to your bricks.
Two coals with the same GCV can fire very differently. One may give an even burn and clean bricks. The other may smoke, clinker and leave you with more under-fired or over-fired bricks per round. The difference is in the rest of the test report.
This matters even more in Nepal because there is still no national minimum standard for the coal kilns burn: the Department of Industry asked the Nepal Bureau of Standards and Metrology to set one, but it had not been drafted when kilns started firing in January 2026 (Kathmandu Post). Until it is, the test report is your main protection. This guide walks through each line, what it means inside a brick kiln, and what to watch out for before you buy.
What a coal test report contains
A coal test report, often called a Certificate of Analysis (COA), is issued by a laboratory or inspection company after testing a sample of the coal. A useful report for a kiln owner has four parts:
- Proximate analysis: moisture, ash, volatile matter and fixed carbon. Together these four describe what the coal is made of and should add up to about 100%.
- Sulphur: usually reported as total sulphur.
- Calorific value: the GCV, in kcal/kg — and it should say on what basis (as received, air-dried and so on).
- Other tests: sometimes ash fusion temperature (how easily the ash melts) and size distribution.
The report should also show who tested it, when, and which cargo or stockpile the sample came from. Those details matter as much as the numbers.
What each number means inside your kiln
| Parameter | What it measures | What it means for your kiln | What you generally want |
|---|---|---|---|
| Moisture | Water held in the coal | You pay for water by the tonne, and the kiln spends heat drying it off before the coal burns | Lower |
| Ash | Mineral matter that does not burn | Adds weight but no heat, leaves residue to clear, and raises the risk of clinker | Lower |
| Volatile matter | Gases released as the coal heats | Helps the coal catch fire quickly and burn with a longer flame; too much can mean smoke and fast, uneven burning | A level that suits your kiln and feeding practice |
| Fixed carbon | The solid carbon left after volatiles burn off | Gives a slow, steady heat that holds temperature through the firing zone | Higher, balanced with volatile matter |
| Sulphur | Sulphur content of the coal | Burns to sulphur dioxide, adding to emissions, and can contribute to salt deposits and discolouration on the brick surface (scumming or efflorescence) | Lower |
| GCV | Heat released per kilogram | The heat on offer — but only in combination with everything above | Higher, judged with the rest |
| Ash fusion temperature | Temperature at which ash softens | Ash that melts easily forms clinker that sticks to bricks and blocks feed holes | Higher |
| Size | Lump size range | Too many fines are lost or burn poorly; oversize lumps burn unevenly | The range your kiln is set up to feed |
Volatile matter and fixed carbon work as a pair. Volatile matter gets the fire going and spreads it. Fixed carbon keeps it going. Most brick kiln operators in the region prefer coal with good volatile matter and low ash, but the right balance depends on your kiln design and how your firemen feed it.
Moisture and ash quietly raise your real cost. Every percentage point of moisture or ash is weight you pay to buy, transport and handle, but that gives no heat. When comparing two offers, look at how much of each tonne will actually burn.
Watch the basis of the GCV. The same coal shows a different GCV depending on whether it is reported as received, air-dried or dry, and some offers quote net (NAR) rather than gross values. Make sure you compare offers on the same basis — see How to Choose the Right Coal GCV for Your Brick Kiln.
Red flags on a test report
A test report is only as good as the sample behind it. Be careful when you see any of these:
- An old date. A report from months ago may describe a different stockpile or cargo, not the coal you are buying.
- No link to your cargo. The report should name the vessel, stockpile or lot. A general "typical analysis" is a sales sheet, not a test.
- Missing or hidden fields. Blank or blacked-out lab names, sample details or quantities deserve a question.
- Only GCV shown. A report that lists calorific value but not ash, moisture, volatile matter and sulphur is hiding the parts that matter to you.
- Numbers that don't add up. Moisture, ash, volatile matter and fixed carbon should total about 100% on the same basis. Mixed-up units or totals far off 100 point to a careless or edited report.
- An unknown laboratory. Prefer reports from recognised inspection companies or accredited labs.
A quick checklist before you buy
- Ask for the full test report, not just the GCV.
- Check the date and that the report belongs to the coal you are buying.
- Look at moisture and ash together: how much of each tonne will actually burn?
- Check volatile matter and fixed carbon against what fires well in your kiln.
- Check sulphur and, if available, ash fusion temperature.
- Confirm the size range suits your feeding.
- For a new source, try a small lot before committing the season.
- Agree how the coal will be sampled and tested on delivery, in case of a dispute.
The best coal for your kiln is the one that gives you the most good bricks, round after round. The test report is how you find it before you pay for it. For the full buying process, see our coal buying checklist for brick kilns.
Frequently asked questions
What is a good ash content for brick kiln coal?
Lower is generally better, because ash adds weight but no heat and raises the risk of clinker. The right level depends on your kiln and the grades available, so compare offers on the full report — moisture, ash, volatile matter, fixed carbon and sulphur together — rather than on one number.
Is higher GCV coal always better for a brick kiln?
No. GCV is the heat on offer, but how the coal ignites, spreads its flame, clinkers and leaves ash decides how many good bricks you get. Two coals with the same GCV can fire very differently.
Does Nepal have a quality standard for kiln coal?
Not yet. The Department of Industry asked the Nepal Bureau of Standards and Metrology to set minimum coal standards, but none had been drafted as of January 2026. Until then, a full, recent test report from a recognised lab is the best protection for buyers.
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