Foot pounds-force second to Joules/hour

James Watt calculated that a mill horse could turn a mill wheel 144 times per hour, doing 32,572 ft·lbf of work per minute — he rounded up to 33,000 ft·lbf/min (550 ft·lbf/s) for marketing purposes. He wanted to sell steam engines by comparing them to horses, so he likely overestimated the horse to make his engines look like better value. A real horse sustains closer to 350–500 ft·lbf/s, so Watt's "1 HP" is actually more than one horse.

Power (ft·lbf/s) = Torque (ft·lbf) × RPM × 2π / 60. This is the workhorse formula (pun intended) of US mechanical engineering. For example, an engine producing 200 ft·lbf of torque at 3,000 RPM delivers 200 × 3,000 × 6.2832 / 60 = 62,832 ft·lbf/s ≈ 114 hp. The formula works because angular velocity in rad/s times torque in ft·lbf gives power directly in ft·lbf/s.

Pushing with 1 pound of force at 1 foot per second — roughly the effort of slowly sliding a light book across a table against friction. Lifting a 1-pound weight 1 foot in 1 second. Turning a doorknob with a very light touch. It's about 1.36 watts — enough to dimly light an LED. In human terms, it's almost effortless: casual walking produces about 50–80 ft·lbf/s of mechanical power, and you don't even notice.

Yes, particularly in ballistics (muzzle energy rates), mechanical testing (dynamometer output), agricultural machinery specs, and industrial equipment designed for the US market. However, even in the US, many engineering firms are switching to SI units for international compatibility. The automotive industry increasingly quotes power in both hp and kW. Aerospace has been mostly metric since the 1990s. Ft·lbf/s survives mainly in traditional mechanical and manufacturing industries.

Bullets are rated in ft·lbf of muzzle energy (not per second), but the power of a firearm is the muzzle energy divided by barrel time. A .308 rifle bullet exits with about 2,600 ft·lbf of energy over a barrel transit time of ~0.001 seconds, meaning the instantaneous power is roughly 2,600,000 ft·lbf/s (about 3,500 hp). That's why rifle recoil feels punchy — for a millisecond, you're absorbing the reaction force of a truck engine.

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.

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.

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.

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.

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.