Heater Power for Heating a Liquid Calculator
Electrical heater rating to raise a volume of water or similar liquid by a set temperature in a set time. With the formula, a worked example and typical values.
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Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
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About this calculator
This page calculates heat energy needed and heater rating from liquid volume, temperature rise, heating time, heater and tank efficiency and 1 more input. Change any value or its unit and the result updates. The steps below show the working for the default values, so you can check each line against your own method.
Limits of this calculator
Add margin for standing losses on long heat-ups, and check the supply current with the three-phase current calculator.
Cross-check: 6 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review.
Verification status: Indicative
Indicative. Estimation only; further engineering checks are required. Basis: Heating estimate without losses unless entered.
What this calculator checks
- The arithmetic of the simplified model for the values you entered.
What remains unverified
- Whether the simplifying assumptions listed on this page hold for your case.
- Any standard, manufacturer or site data. Treat the result as an estimate and confirm it by a further engineering check.
Verification register entry
| Calculation author | Rahul Sharma (author) |
|---|---|
| Technical review | No independent technical review has been carried out |
| Individual professional approval | Not recorded |
| Formula reference | not recorded |
| Standard and edition | Not applicable: The heat-energy equation is a general thermodynamic identity. Heater sizing standards depend on the equipment and application, not this generic equation. |
| Standard review state | Not applicable |
| Scope-screening note | not recorded |
| Cross-check test cases | 6 reference vectors (tests/reference_vectors.json) |
| Review date | not recorded |
| Next review date | not recorded |
| Status | Indicative |
Needed before this calculator can be marked Verified: reviewer name, qualification and review date; exact formula reference; formula source (textbook or standard); next review date.
Formula
Worked example
| Input | Value |
|---|---|
| Liquid volume | 1,000 L |
| Temperature rise (K) | 40 |
| Heating time | 2 h |
| Heater and tank efficiency | 0.9 |
| Specific heat (kJ/kg·K) | 4.186 |
- Q = 1,000 kg × 4.186 × 40 K = 167.4 MJ = 46.51 kWh
- P = 46.51 kWh / (2 h × 0.9) = 25.84 kW
Assumptions
- 1 L of water is 1 kg
- Losses during heating are lumped in the efficiency
Add margin for standing losses on long heat-ups, and check the supply current with the three-phase current calculator.
Inputs and results
| Input | Unit | Allowed or shown | Note |
|---|---|---|---|
| Liquid volume | L | greater than 0 L | |
| Temperature rise (K) | (number) | greater than 0, up to 100 | |
| Heating time | h | greater than 0 h | |
| Heater and tank efficiency | (number) | greater than 0, up to 1 | |
| Specific heat (kJ/kg·K) | (number) | 0.5 or more, up to 10 |
| Result | Unit | Allowed or shown | Note |
|---|---|---|---|
| Heat energy needed | kWh | Shown to 2 decimal places | |
| Heater rating | kW | Shown to 2 decimal places |
How it is calculated
Each input is converted to the base unit of its quantity, the formula above is applied in the order shown in the worked example, and each result is shown in the unit you choose. Results are held at full precision and rounded only for display, except where a step selects a standard size, as the worked example shows. A value outside its allowed range is refused with a message instead of giving a result.
How the result changes with liquid volume
| Liquid volume (L) | Heat energy needed (kWh) | Heater rating (kW) |
|---|---|---|
| 100 | 4.65 | 2.58 |
| 250 | 11.63 | 6.46 |
| 500 | 23.26 | 12.92 |
| 1,000 | 46.51 | 25.84 |
| 2,000 | 93.02 | 51.68 |
| 4,000 | 186.04 | 103.36 |
| 10,000 | 465.11 | 258.4 |
Other inputs are the same as in the worked example above.
Standards and further reading
- EN 12464-1 (lighting of indoor workplaces)
- CIE publications on photometry
Lamp and luminaire data come from the manufacturer; the illuminance targets that apply come from your project specification and local regulation. These are named as background reading. Elecmetric does not embed clause text or rating tables, and the reviewer record for this calculator is separate from this list.
Frequently asked questions
What do I need to enter?
Enter liquid volume, temperature rise (K), heating time, heater and tank efficiency and specific heat (kJ/kg·K). Change the unit of a value with its selector and the result stays the same.
What does this calculator assume?
1 L of water is 1 kg. Losses during heating are lumped in the efficiency.
Which calculators should I use next?
Common next steps are Current from Power (kW to Amps) and Appliance Running Cost (Energy and Cost). The related links at the bottom of this page open them.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. 6 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review. Check design values against the standard and the equipment data you work to.
Formula guides and reference
Longer explanations with worked examples and tables, written for the same topic.
- Heating Formulas: Energy and Heater Power: Heating formulas for the energy to warm water or another material, heater power for a heat-up time with efficiency
- Specific Heat Converter: J/kg·K, kJ/kg·K and BTU/lb·°F
- Energy and Cost Formulas: kWh and Payback: Energy and cost formulas for kWh from power and hours, running cost, efficiency and payback of an upgrade
- Heat Pump COP Formulas: Heat pump formulas: the coefficient of performance, the electrical power for a heating load
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