Heat loss from brewery kettles, tuns & whirlpool — and how to cut it
Bare brewhouse vessels radiate heat all day. Here is how much each one loses, and what removable insulation recovers.
Every hot vessel in the brewhouse is a radiator. A bare stainless kettle head at boiling temperature loses heat to the hall every minute it is hot — and across a brew day that is real fuel and real money. This guide quantifies the loss for each brewhouse vessel and shows what removable insulation recovers.
How much each vessel loses
The figures below are bare-surface heat loss per square metre on the Inzonex canonical model: combined convection and radiation (ISO 12241), a lightly-ventilated hall at 25 °C with 0.5 m/s air, emissivity 0.9 for oxidised/painted steel. The hotter the surface, the steeper the loss — radiation scales with the fourth power of absolute temperature.
| Vessel | Surface °C | Bare W/m² | Insulated | Cut |
|---|---|---|---|---|
| Wort (brew) kettle | 99 | 1,138 | 60 | 95% |
| Cereal / adjunct cooker | 95 | 1,066 | 56 | 95% |
| Whirlpool | 92 | 1,013 | 53 | 95% |
| Lauter tun | 77 | 759 | 40 | 95% |
| Mash tun | 68 | 615 | 32 | 95% |
What we actually insulate
On most brewhouse vessels the biggest exposed area is the conical or domed roof — that is what Inzonex covers, leaving manways, sight glasses and agitator drives accessible. A 50 mm mineral-wool lamella core with a silicone or PTFE outer jacket brings the surface from 70–99 °C down to roughly 30 °C: touch-safe (≤45 °C) and about 95% less loss.
Calculate your own vessels
Each vessel has its own interactive 3D heat-explorer: wort kettle, mash tun, lauter tun, whirlpool and cooker — enter your area and temperature to see kW, € and CO&sub2; saved.
The method: ASTM C680 combined convection and radiation
Heat loss from brewhouse vessels depends on three factors: the temperature difference between surface and ambient air, the exposed surface area, and the insulation material's thermal conductivity. On a wort kettle at 99°C in a 25°C brewhouse, a bare stainless surface loses heat via natural convection (approximately 8 W/m²·K) and thermal radiation (approximately 2 W/m²·K under the Stefan–Boltzmann law), totalling about 10 W/m²·K. That translates to 1,138 W/m² on a 99°C surface—a substantial and continuous loss every brew day.
The formula is simple: Q = ho × A × ΔT, where ho is the surface film coefficient (10 W/m²·K for still-air brewing), A is the exposed area, and ΔT is the temperature difference. Insulation adds thermal resistance in series, cutting the flux logarithmically as thickness rises.
Economics: one kettle, one year
A typical wort kettle roof covers about 9 m² of surface. Bare and running at 99°C, that loses roughly 10 kW continuously. Over a 50-brew-day season, or year-round operation, the annual loss reaches 32–80 MWh of wasted fuel. At €0.07/kWh, a single kettle uninsulated costs €2,200–5,600/year in pure energy loss—not counting the extended brew cycles from cooling losses or the ambient temperature bump that forces HVAC to run longer.
Removable insulation (50 mm mineral wool, k ≈ 0.04 W/m·K) cuts that loss by approximately 95%, bringing the surface to roughly 30°C (touch-safe, ≤45°C per ASTM C1055 and EN ISO 13732-1) and saving €2,000–5,300/year. Payback on modular removable insulation: typically 6–18 months for breweries running year-round, less for seasonal setups with winter idle time.
Why removable insulation?
Permanent lagging (rigid fiberglass wrapped in metal, or welded covers) gets cut off during maintenance—dents, leaks, or bearing replacement—and is rarely (if ever) replaced. Once removed, a €5,000 investment becomes dead cost: the vessel runs bare again, losing its a site-specific amount (estimate it with the calculator) savings. Inzonex modular covers snap on with a functional zipper. Removal takes minutes, no cutting, no waste. The insulation comes off, stays intact, and refits exactly. Over a 10-year vessel lifecycle, continuous insulation delivers 10× more cost and CO₂ value than rigid lagging ever cut off after year two.
FAQ
How much heat does a brewery kettle lose?
A bare wort-kettle surface at 99 °C loses about 1,138 W per square metre by convection and radiation in a typical brewhouse. Removable insulation cuts it by about 95%.
What is the surface temperature of a mash tun?
Around 68 °C during the saccharification rest, rising toward 77 °C at mash-out in the lauter tun. These surface temperatures set the heat-loss rate.
Does insulating the kettle affect the boil?
Insulating the kettle head and shell holds the boil with less energy and reduces the gas needed to reach a vigorous boil, without affecting evaporation through the vent.