Electric Kiln Design Calculator
Electric Kiln builder tool for designing and estimating materials and costs. Automatic brick count, optimization, heat transfer and insulation. Recommended power requirements methods.
Dennis Allende
One of many troubles that I have been experiencing is not finding a good single source of information when building a kiln. There are a lot of good tutorials with clear explanations but in my search some questions were always unanswered clearly.
One of my uncertainties was if it was enough power to reach cone 6, how much power is required, should it be according to the volume? the surface? the bigger the kiln the more efficient it gets per volume. What if it cools too slowly? What if the maximum power of my house is fixed at around 5000W, can I still use a kiln? how big?
So with all of those questions in mind, with all of my sheets of calculations in multiple parts and some papers going around, I decided to gather all of that in a single simple tool. This allows to clearly play with dimensions and materials and get a notion of how the parts interact with each other.
Of course I have never, and probably never will, build a giant kiln for a factory. I really don't know which factors you have to consider there. But at low scale I think I am getting close to at least having some rest in my doubts.
Most of the power propositions are based on The Kiln Book 4th Edition from Frederick Olsen. He suggests 3 ways of determining the power of a kiln: considering the volume, the surface, and a compiled table of common kilns. I expanded this list with my own compilation of 66 kilns available in the market. With that information I got the median value for volume and surface. I present all of those values as suggestions and finally an experimental one compiled from the heat loss of the system.
I strongly recommend always going a little higher, but when the power available is low it is good to know what is possible. Even so, take it with a grain of salt. You can check all of the sources at the references section at the bottom of the page.
The default settings consider using K23 bricks (9x4.5x3) and 4 inches of fiber insulation. You can configure if you want to build over the base or around. You can also manually enter dimensions for each type of brick, that way if you want to use the long part of a brick for a wall thickness you just modify that dimension.
You can play with this tool and tell me what are your thoughts on it. If you find some errors please comment here so I can review it. Thanks for your feedback.
TODO
- Automatic elements calculation
- Round Kiln Support
Kiln Builder
by Dennis Allende
Insulation Configuration
Fire Brick Layer
Ceramic Fiber Insulation
Combined Insulation
Heat Transfer Analysis
Conduction Through Walls
External Surface Losses
Heat Balance Verification
Power Requirements & Recommendations
Minimum Power (Heat Loss Only)
Industry Standard Methods
Practical Power Recommendation
✓ Heating pottery load
✓ Reasonable heat-up time
References
Bibliography:
Olsen, Frederick L. (2014). The Kiln Book (4th ed.). Iola, WI: Krause Publications.
Schonert, M. (2016). "Heat Transfer Calculations." RepKiln Project. https://hackaday.io/project/21642-repkiln/log/59173-heat-transfer-calculations
The Edward Orton Jr. Ceramic Foundation. "Pyrometric Cone Temperature Chart" (self-supporting cones at 60°C/hr heating rate). Official Chart PDF
Detailed Calculation Formulas:
A. Complete Heat Transfer Analysis:
• Steady-state: Heat through walls = Heat from surface
• Conduction: Q = (T_interior - T_surface) × A_interior / R_total
• Convection: Q_conv = h × A_exterior × (T_surface - T_ambient)
Natural convection coefficient (h): 4-10 W/m²K
• Radiation: Q_rad = ε × σ × A × (T_s⁴ - T_a⁴)
Emissivity (ε): 0.9, Stefan-Boltzmann (σ): 5.67×10⁻⁸ W/m²K⁴
• Surface temperature found iteratively where conduction = convection + radiation
B. R-Value (Thermal Resistance) Calculation:
• R = thickness(m) / thermal_conductivity(W/mK)
• R_brick = brick_thickness_m / k_brick
• R_ceramic_fiber = fiber_thickness_m / k_ceramic_fiber
• R_total = R_brick + R_ceramic_fiber (series addition)
C. Thermal Conductivity Values:
• K-23 firebrick: k = 0.12 W/mK
• K-26 firebrick: k = 0.15 W/mK
• Ceramic fiber (64 kg/m³): k = 0.16 W/mK
• Ceramic fiber (96 kg/m³): k = 0.14 W/mK
• Ceramic fiber (128 kg/m³): k = 0.12 W/mK (optimal)
• Ceramic fiber (160 kg/m³): k = 0.11 W/mK
• Ceramic fiber (192 kg/m³): k = 0.10 W/mK
• Note: Higher density = lower k-value = better insulation
• Values at mean temperature (~500-600°C)
D. Heat Transfer Analysis (Steady-State):
• Conduction through walls: Q = (T_interior - T_surface) × A_interior / R_total
• Convection from surface: Q_conv = h × A_exterior × (T_surface - T_ambient)
• Radiation from surface: Q_rad = ε × σ × A_exterior × (T_surface⁴ - T_ambient⁴)
• Convection coefficient (h): 4-10 W/m²K (temperature-dependent)
• Emissivity (ε): 0.9 for typical painted/oxidized metal surfaces
• Stefan-Boltzmann constant (σ): 5.67×10⁻⁸ W/m²K⁴
• In steady state: Q_conduction = Q_convection + Q_radiation
• Surface temperature found iteratively using Newton-Raphson method (100 max iterations)
• Convergence criteria: |error| < 0.5W or |error/Q| < 0.1%
E. Real-World Kiln Power Analysis:
• Skutt KM-1027 (7 ft³ / 198 L, 23×23×27"): 11,520W = 58 W/L
• Industry formulas (72 W/L, 4.2 W/in²) assume minimal insulation (2.5" brick only)
• Modern well-insulated kilns use 30-50% less power than industry formulas
• Total power requirement = Heat loss + Heating thermal mass + Heating pottery
• Thermal mass energy: E = mass × c × ΔT
Example: 245 kg brick × 0.84 kJ/kg·K × 1197 K = 247 MJ = 68 kWh
Over 6-8 hour firing: 10-14 kW average power during heat-up
• Steady-state heat loss (this calculator) is only maintenance requirement at temperature
F. Power Calculation Methods Summary:
• Market Volume Median: P = V_interior_L × 72 W/L (V_interior_in³ × 1.18 W/in³)
• Market Surface Median: P = A_interior_cm² × 0.65 W/cm² (A_interior_in² × 4.2 W/in²)
• Olsen Method 1: P = V_interior_in³ × 1.35 W/in³ (average of 1.2-1.5)
• Olsen Method 2: P = A_interior_in² × 6 W/in² (average of 5-7)
• Note: These formulas overestimate for well-insulated kilns
G. Heat Loss Reduction Calculation:
• Heat_Loss_Without_Insulation = (ΔT × A) / R_brick_only
• Reduction_% = ((Loss_without - Loss_with) / Loss_without) × 100
H. Unit Conversions:
• Inches to meters: multiply by 0.0254
• Square inches to square cm: multiply by 6.4516
• °F to °C: (°F - 32) × 5/9
• Interior volume (in³): W_in × D_in × H_in
• Interior surface area (in²): 2×(W×D + W×H + D×H)
Olsen Electrical Specifications Table (Table 9-1):
* Range shows closest volume match from Olsen's table. User should make final power selection.
| Volume (ft³) | Kilowatts | Volts | Amps | Elements |
|---|---|---|---|---|
| 1 | 1.8 | 120 | 15 | - |
| 2 | 4.6 | 230 | 20 | - |
| 5.5 | 220/240 | 25 | 3 | |
| 4.6 | 230/208 | 20 (3φ) | 3 | |
| 3 | 5.3 | 230 | 23 | 3 |
| 5.1 | 230 | 22 | 4 | |
| 5.8 | 240 | 24 | 4 | |
| 4 | 8.1 | 230 | 35 | 4 |
| 11.0 | 208/240 | 26.6 (3φ) | - | |
| 10.8 | 240 | 45 | - | |
| 5 | 14.4 | 220/240 | 60 | - |
| 8.9 | 230 | 38.5 | - | |
| 7.8 | 230 | 34 | - | |
| 6 | 9.2 | 230 | 40 | 5 |
| 7 | 16.8 | 220/240 | 70 | - |
| 11.3 | 230 | 47 | - | |
| 8 | 14.4 | 220/240 | 60 | - |
| 10.4 | 230 | 45 | 5 | |
| 9.2 | 230 | 40 | 5 | |
| 10 | 13.8 | 230 | 60 | 6 |
| 26.0 | 240 | 108 | - | |
| 13 | 30.0 | 220/240 | 125 | - |
| 24.0 | 220/240 | 100 | - | |
| 25.0 | 220/240 | 75 | - | |
| 15 | 34.5 | 230 | 150 | 6 |
| 16 | 36.0 | 220/240 | 150 | - |
| 30.0 | 220/240 | 125 | - | |
| 24.0 | 240 | 100 | 5 |
Comprehensive Market Data (66 Electric Kilns):
• Median: 0.65 W/cm² (4.2 W/in²) surface density, 72 W/L (2040 W/ft³) volume density
• Average: 0.67 W/cm² (4.3 W/in²) surface density, 92.8 W/L (2628 W/ft³) volume density
| Brand/Model | Volume L (ft³) | Watts | W/cm² (W/in²) | W/L (W/ft³) | Wall |
|---|---|---|---|---|---|
| Skutt FireBox 8×4 | 5 (0.2) | 1800 | 1.03 (6.6) | 383 (10.8) | 2.0 |
| Skutt FireBox 8×6 | 6 (0.2) | 1800 | 0.88 (5.7) | 287 (8.1) | 2.0 |
| L&L Plug-n-Fire | 9 (0.3) | 1500 | 0.56 (3.6) | 159 (4.5) | 2.0 |
| Olympic HB89E | 9 (0.3) | 1800 | 0.67 (4.3) | 191 (5.4) | 2.0 |
| L&L DLH11-DX | 14 (0.5) | 2800 | 0.87 (5.6) | 200 (5.7) | 2.5 |
| Nabertherm Top 16/R | 15 (0.5) | 2600 | 0.76 (4.9) | 171 (4.8) | 2.5 |
| Cress ET911 | 18 (0.6) | 1500 | 0.37 (2.4) | 84 (2.4) | 2.5 |
| Skutt KM-614-3 | 21 (0.7) | 2300 | 0.54 (3.5) | 110 (3.1) | 2.5 |
| Paragon GL64 | 32 (1.1) | 3600 | 0.64 (4.1) | 113 (3.2) | 2.0 |
| Evenheat Studio Pro | 33 (1.2) | 2880 | 0.49 (3.2) | 87 (2.5) | 2.0 |
| Jen-Ken AF 1513 | 42 (1.5) | 6240 | 0.91 (5.9) | 150 (4.2) | 2.5 |
| Rohde Ecotop 43 | 43 (1.5) | 2900 | 0.42 (2.7) | 67 (1.9) | 1.4* |
| L&L e14S-3 | 49 (1.7) | 4980 | 0.67 (4.3) | 102 (2.9) | 3.0 |
| Evenheat HF 1813 | 53 (1.9) | 5500 | 0.70 (4.5) | 103 (2.9) | 2.5 |
| Cone Art 1813D | 54 (1.9) | 5500 | 0.73 (4.7) | 101 (2.9) | 3.5 |
| Rohde Ecotop 60 | 60 (2.1) | 3600 | 0.43 (2.7) | 60 (1.7) | 1.4* |
| L&L e18S-3 | 63 (2.2) | 5740 | 0.65 (4.2) | 91 (2.6) | 3.0 |
| Jen-Ken AF 1815 | 66 (2.3) | 7200 | 0.76 (4.9) | 108 (3.1) | 2.5 |
| Kittec CB 70 S | 70 (2.5) | 4800 | 0.55 (3.5) | 69 (1.9) | 2.8 |
| Olympic 1818E | 71 (2.5) | 5040 | 0.53 (3.4) | 71 (2.0) | 2.5 |
| Skutt KM-818 | 71 (2.5) | 6660 | 0.70 (4.5) | 93 (2.6) | 2.5 |
| Cress E18 | 74 (2.6) | 5300 | 0.61 (3.9) | 72 (2.0) | 2.5 |
| Paragon TNF823 | 78 (2.8) | 7200 | 0.71 (4.6) | 92 (2.6) | 3.0 |
| AMACO EX-232SF | 87 (3.1) | 6500 | 0.60 (3.9) | 75 (2.1) | 2.5 |
| Cress E23 | 93 (3.3) | 8600 | 0.84 (5.4) | 92 (2.6) | 2.5 |
| Kittec CB 100 S | 95 (3.4) | 7200 | 0.67 (4.3) | 75 (2.1) | 2.8 |
| L&L e18T-3 | 95 (3.4) | 7500 | 0.64 (4.1) | 79 (2.2) | 3.0 |
| Nabertherm N 100 | 112 (4.0) | 9000 | 0.65 (4.2) | 80 (2.3) | 3.0 |
| Skutt KM-1018-3 | 114 (4.0) | 8400 | 0.64 (4.1) | 74 (2.1) | 3.0 |
| L&L e23S-3 | 115 (4.1) | 8640 | 0.66 (4.3) | 75 (2.1) | 3.0 |
| Cone Art 2318D | 123 (4.3) | 9000 | 0.67 (4.3) | 73 (2.1) | 3.5 |
| MEDIAN (33rd kiln) | - | - | 0.65 (4.2) | 72 (2.0) | - |
| Jen-Ken AF3C 1822 | 143 (5.0) | 8640 | 0.60 (3.9) | 61 (1.7) | 2.5 |
| Olympic 2518HE | 145 (5.1) | 8160 | 0.57 (3.7) | 56 (1.6) | 3.0 |
| L&L e23T-3 | 173 (6.1) | 11520 | 0.67 (4.3) | 67 (1.9) | 3.0 |
| Skutt KM-1027-3 | 174 (6.1) | 11520 | 0.67 (4.3) | 66 (1.9) | 2.5 |
| AMACO EX-257SF | 177 (6.3) | 10800 | 0.64 (4.1) | 61 (1.7) | 2.5 |
| Cress E24HP | 179 (6.3) | 14000 | 0.84 (5.4) | 78 (2.2) | 3.0 |
| L&L e28S-3 | 182 (6.4) | 10800 | 0.60 (3.9) | 59 (1.7) | 3.0 |
| Evenheat HF 2327 | 192 (6.8) | 9800 | 0.53 (3.4) | 51 (1.4) | 2.5 |
| Nabertherm N 200 | 197 (7.0) | 15000 | 0.75 (4.8) | 76 (2.1) | 3.0 |
| Evenheat RM 2329 | 206 (7.3) | 10800 | 0.56 (3.6) | 52 (1.5) | 2.5 |
| AMACO HF-101 | 217 (7.7) | 13400 | 0.69 (4.5) | 62 (1.8) | 5.0 |
| Jen-Ken AF 2822 | 222 (7.8) | 11520 | 0.58 (3.7) | 52 (1.5) | 3.0 |
| L&L eQ2327-3 eQuad | 234 (8.3) | 19510 | 0.90 (5.8) | 83 (2.4) | 3.0 |
| Paragon Dragon 24 | 255 (9.0) | 16500 | 0.69 (4.5) | 65 (1.8) | 4.0 |
| Skutt KM-1227-3 | 267 (9.4) | 11520 | 0.49 (3.2) | 43 (1.2) | 3.0 |
| Bailey TL-2327-10 | 272 (9.6) | 13500 | 0.58 (3.7) | 50 (1.4) | 4.5 |
| Bailey TL-2827 | 272 (9.6) | 13500 | 0.58 (3.7) | 50 (1.4) | 4.5 |
| L&L e28T-3 | 272 (9.6) | 16620 | 0.71 (4.6) | 61 (1.7) | 3.0 |
| Olympic 2827HE | 278 (9.8) | 12000 | 0.51 (3.3) | 43 (1.2) | 3.0 |
| AMACO HF-105 | 282 (10.0) | 18000 | 0.77 (5.0) | 64 (1.8) | 5.0 |
| Olympic Oval 2030E | 295 (10.4) | 15680 | 0.64 (4.1) | 53 (1.5) | 3.0 |
| Olympic 3027HE | 313 (11.1) | 14400 | 0.57 (3.7) | 46 (1.3) | 3.0 |
| Bailey TL-4222 | 333 (11.8) | 15500 | 0.61 (3.9) | 47 (1.3) | 4.5 |
| Paragon Super Dragon | 340 (12.0) | 22000 | 0.75 (4.8) | 65 (1.8) | 4.0 |
| Jen-Ken JK² 29" | 347 (12.2) | 13200 | 0.45 (2.9) | 38 (1.1) | 3.0 |
| Skutt KM-1227-3PK | 366 (12.9) | 23600 | 0.83 (5.3) | 64 (1.8) | 3.0 |
| L&L T2327-D DaVinci | 413 (14.6) | 26013 | 0.78 (5.0) | 63 (1.8) | 3.5 |
| Cress FXC30FH | 442 (15.6) | 18000 | 0.61 (3.9) | 41 (1.2) | 6.5 |
| L&L T2336-D DaVinci | 551 (19.5) | 32515 | 0.80 (5.2) | 59 (1.7) | 3.5 |
| Bailey Commercial | 603 (21.3) | 22000 | 0.62 (4.0) | 36 (1.0) | 7.0 |
*Microporous insulation. Sample of 66 electric kilns analyzed.
