Heat Transfer Converter
Convert a heat transfer rate between watts, kilowatts, megawatts, calories per second, and BTU-based units. Enter a rate, then select the From unit and To unit.
Convert Heat Transfer Between Units
Heat Transfer Formula
Where:
- \(\dot Q_{\mathrm{from}}\) — the entered heat transfer rate in the selected From unit
- \(\dot Q_{\mathrm{to}}\) — the converted heat transfer rate in the selected To unit
- \(f_{\mathrm{from}}\) and \(f_{\mathrm{to}}\) — the number of watts per unit for the selected units
The converter first expresses the entered rate in watts, then divides by the watts-per-unit factor for the destination unit. Because these are rates of energy transfer, their conversion factors are the same as those used for power.
Heat Transfer – Calculation Example
Example: convert the default value of 500 watts to kilowatts. One kilowatt equals 1,000 watts.
\[500\ \mathrm{W}\times\frac{1\ \mathrm{W/W}}{1{,}000\ \mathrm{W/kW}}=0.5\ \mathrm{kW}\]
Result: 500 W = 0.5 kW.
How to use the calculator
- Enter a nonnegative number in Heat transfer rate. The number is interpreted in the unit you choose next; you do not need to type a unit in the field.
- Choose the unit of your entered value under From unit. For example, select Watt (W) if your value is in watts.
- Choose the unit you want under To unit. For example, select Kilowatt (kW) to express the rate in kilowatts.
- Read Converted Heat Transfer. The result includes the destination unit and is displayed to a maximum of eight decimal places.
Both menus offer W, kW, MW, cal/s, kcal/s, BTU/s, BTU/min, and BTU/h. You can convert in either direction, such as W to BTU/h or BTU/h to W. Selecting the same unit in both menus leaves the value unchanged.
What a heat transfer rate means
A heat transfer rate tells you how much thermal energy moves between systems per unit of time. It is commonly written as \(\dot Q\). One watt is one joule per second, so a heat transfer rate of 500 W means energy is being transferred at 500 joules each second. The converter changes the unit used to express that rate; it does not change the physical amount of heat being transferred.
Heat transfer rates appear in heating and cooling specifications, heat exchanger calculations, and assessments of heat loss through walls or equipment. They are distinct from total heat energy: a rate in W or BTU/h does not tell you the total energy transferred unless you also know the duration. At a constant rate, multiplying the rate by time gives the transferred energy in matching units—for example, W multiplied by seconds gives joules.
A larger converted number does not necessarily mean more heat transfer. The numerical value changes with the size of the unit: 1 kW and 1,000 W describe the same rate. When comparing equipment or calculations, convert all rates to a common unit first. If you need to relate a rate to the area it crosses, use a heat flux density converter; heat flux density is a rate per unit area, not another unit of total heat transfer rate.
Conversion factors and practical limits
The calculator uses watts as its intermediate unit. The following table shows the exact factors used by the calculator, expressed as watts per listed unit. These are the factors behind every available conversion, including conversions between two non-watt units.
| Unit | Watts per unit |
|---|---|
| W | 1 |
| kW | 1,000 |
| MW | 1,000,000 |
| cal/s | 4.184 |
| kcal/s | 4,184 |
| BTU/s | 1,055.06 |
| BTU/min | 17.5843 |
| BTU/h | 0.29307107 |
The calorie factors use 1 calorie = 4.184 joules. BTU conversions depend slightly on the BTU definition and reference convention; the table states the approximate factors this calculator applies. The BTU factors are rounded independently, so a result may differ slightly from one obtained by converting between BTU time units using time alone. Display rounding can also hide small nonzero values; for high-precision work, retain more digits in your source calculation.
The input accepts zero and positive rates, but not negative values. It therefore cannot represent direction with a sign: specify the direction of heat flow separately when that matters. This is a unit converter, not a heat-transfer model. It cannot determine a rate from temperature difference, surface area, or material properties. For those calculations, you may also need thermal conductivity or specific heat, depending on the situation.
Frequently Asked Questions
How do I convert BTU/h to kW by hand?
Multiply the BTU/h value by 0.29307107 to get watts, then divide by 1,000 to get kilowatts. For example, \(12{,}000\ \mathrm{BTU/h}\times 0.29307107\div 1{,}000\approx 3.51685\ \mathrm{kW}\). This uses the BTU convention applied by this converter; another reference may give a slightly different result.
What is a normal or good heat transfer rate?
There is no universally good heat transfer rate. The appropriate value depends on what you are heating or cooling, its size, the temperature difference, and the desired outcome. A rate that is useful for a small room may be inadequate for a building. Compare rates only after putting them in the same unit and considering the conditions they describe.
How many BTU/h are in 1 kW?
Using this converter’s factor, 1 kW is approximately 3,412.14 BTU/h. To estimate BTU/h from kW, multiply the kW value by 3,412.14; to go the other way, divide by that number. Published figures may vary slightly because BTU definitions and rounded conversion factors differ.
Is kcal/s the same as food Calories per second?
Yes, if “Calorie” means the dietary Calorie: one food Calorie, written Cal, equals one kilocalorie, written kcal. A lowercase calorie, cal, is one-thousandth of a kcal. Capitalization matters, so check whether a source means cal/s or kcal/s before converting.
Does a cooling capacity of 12,000 BTU/h mean the appliance uses 3.52 kW of electricity?
No. About 3.52 kW is the appliance’s cooling rate expressed in kilowatts, not necessarily its electrical input. A heat pump or air conditioner can move more heat than the electrical energy it consumes. To estimate electricity use, consult its rated input power or an applicable efficiency measure such as COP.
How can I estimate heat transfer rate from fluid flow and temperature change?
For a fluid with known mass flow rate and specific heat capacity, use \(\dot Q=\dot m c_p\Delta T\). If mass flow is in kg/s, specific heat is in J/(kg·K), and temperature change is in K, the result is in watts. This is an estimate when properties vary significantly or heat is lost elsewhere; it also needs a different treatment during phase changes.
Can I convert BTU/h directly to BTU or kWh?
Not without a duration: BTU/h is a rate, while BTU and kWh are amounts of energy. If the rate stays constant, multiply it by the elapsed time. For example, 12,000 BTU/h sustained for two hours transfers 24,000 BTU, or approximately 7.03 kWh. If the rate changes, calculate the energy over each interval or integrate the rate over time.
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