Joules/hour to Calories (th)/second
J/h
cal(th)/s
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
1 J/h (Joules/hour) → 0.00006639048226046319 cal(th)/s (Calories (th)/second) Just now |
Quick Reference Table (Joules/hour to Calories (th)/second)
| Joules/hour (J/h) | Calories (th)/second (cal(th)/s) |
|---|---|
| 3,600 | 0.23900573613766749522 |
| 36,000 | 2.3900573613766749522 |
| 360,000 | 23.90057361376674952199 |
| 3,600,000 | 239.00573613766749521989 |
| 10,000,000 | 663.90482260463193116635 |
| 36,000,000 | 2,390.05736137667495219885 |
About Joules/hour (J/h)
Joules per hour (J/h) is a very low power unit, equivalent to approximately 0.000278 watts. It is used in precision calorimetry, passive building heat loss calculations, and biological heat flux measurements where the energy exchange over hours is more meaningful than per-second rates. One watt equals 3,600 J/h. The unit is occasionally seen in nutrition science and environmental physiology, where energy budgets are tracked over hours.
A sleeping mouse dissipates roughly 720,000 J/h (~200 W/kg) due to its high surface-area-to-volume ratio. A well-insulated house loses about 36,000,000 J/h (10 kW) on a cold winter day.
About Calories (th)/second (cal(th)/s)
Calories (thermochemical) per second (cal(th)/s) equals 4.184 watts. It is a caloric power unit used in thermochemistry and laboratory heat-flow measurements where energy is expressed in thermochemical calories rather than joules. Reaction calorimeters and bomb calorimeters sometimes report heat release rates in this unit. It is closely related to the watt but retains the calorie convention of chemistry rather than physics.
A 60 W light bulb dissipates about 14.3 cal(th)/s as heat. A vigorous chemical reaction releasing 100 cal(th)/s generates 418 W of thermal power.
Joules/hour – Frequently Asked Questions
Why use joules per hour instead of just watts?
When you're tracking energy budgets over hours — passive house heat loss, slow battery self-discharge, biological calorimetry — expressing rates in J/h matches the timescale of your measurements. A passive house losing 36 MJ/h is more intuitive to a building physicist than "10 kW" because they're calculating daily heat budgets in megajoules. It's a unit of convenience, not necessity.
How does joules per hour relate to kilowatt-hours?
One kWh = 3,600,000 J, so 3,600,000 J/h = 1 kW. The relationship is elegantly circular: if you consume 3.6 MJ/h of power, you use exactly 1 kWh of energy each hour. This makes J/h a natural bridge unit between the SI energy world (joules) and the practical electricity billing world (kWh). Multiply J/h by hours and you get joules of total energy; divide by 3,600,000 and you get kWh.
What is the heat loss of a well-insulated building in joules per hour?
A Passivhaus-certified building targets heat loss below 54 MJ/h (15 W/m² × 1,000 m² for a typical house). A standard older home might lose 180–360 MJ/h (50–100 kW) on a cold day. The difference is dramatic: triple glazing, 300mm insulation, and air-tightness can reduce heat loss by 80%. Building energy certificates in some countries express this in kWh/m²/year, but the underlying calculation uses J/h or W.
How many joules per hour does a human radiate while sleeping?
About 230,000–290,000 J/h (65–80 W). This drops from your waking basal rate of ~290,000–360,000 J/h (80–100 W) because metabolic rate falls 10–15% during sleep. The heat warms your bed and room measurably — two people sleeping together can raise bedroom temperature by 1–2°C overnight in a small, well-insulated room. It's why you wake up warm even without the heating on.
Is J/h used in any standards or building codes?
Not directly — most building codes use watts per square meter (W/m²) or kWh/m²/year for energy performance ratings. However, the underlying heat transfer calculations in standards like ISO 13790 effectively compute in J/h when assessing hourly energy balances. Some German and Swiss engineering tools output intermediate results in kJ/h or MJ/h. The unit lives in the calculation layer, even if the final certificate uses more familiar units.
Calories (th)/second – Frequently Asked Questions
Why do chemists use calories per second instead of watts?
Tradition and unit consistency. When your energy measurements are in calories (specific heat of water = 1 cal/g/°C makes calculations beautifully clean), expressing rates in cal/s keeps everything in the same system. A chemist measuring how fast a reaction heats 500 mL of water doesn't want to convert to joules just to report a rate. The calorie makes water-based calorimetry arithmetic almost trivial.
What is the difference between a calorie and a Calorie in this context?
The thermochemical calorie (lowercase "c") used in cal/s equals 4.184 joules. The food Calorie (uppercase "C" or kilocalorie) is 1,000× larger at 4,184 joules. So 1 food Calorie/s = 4,184 watts — roughly the power of a space heater. Nutrition labels use kilocalories but write "Calories" with a capital C, creating one of the most persistent unit confusions in science. When you see cal/s in chemistry, it's always the small calorie.
How many cal/s does an exothermic chemical reaction typically release?
It varies enormously. Neutralizing a strong acid with a strong base might release 0.5–5 cal/s in a teaching lab. Combustion of magnesium ribbon produces 50–200 cal/s of intense white-hot heat. Thermite reactions can exceed 10,000 cal/s (42 kW). Explosive decomposition of TNT releases energy at roughly 250,000 cal/s (1 MW) during detonation. The rate depends on both the enthalpy change and how fast the reaction proceeds.
How do you measure heat output in calories per second experimentally?
A reaction calorimeter submerges the reaction vessel in a known mass of water and measures temperature rise over time. If 1,000 g of water rises 0.5°C in 10 seconds, the heat release is 500 cal in 10 seconds = 50 cal/s. Modern isothermal calorimeters use Peltier elements to maintain constant temperature, measuring the electrical power needed to compensate — giving cal/s readings with milliwatt precision.
Is the thermochemical calorie still used in modern research?
Increasingly rarely. IUPAC officially recommends joules, and most modern journals require SI units. However, the calorie persists in biochemistry (metabolic rates), nutrition (food energy), and some physical chemistry subfields where decades of reference data are in calories. Older researchers and textbooks still think in calories. The 4.184 conversion factor is burned into every chemist's brain, even if they wish it weren't.