BTU/hour to Joules/hour
BTU/h
J/h
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Quick Reference Table (BTU/hour to Joules/hour)
| BTU/hour (BTU/h) | Joules/hour (J/h) |
|---|---|
| 5,000 | 5,275,279.26310009977977658952 |
| 8,000 | 8,440,446.82096015964764254323 |
| 12,000 | 12,660,670.23144023947146381485 |
| 18,000 | 18,991,005.34716035920719572227 |
| 36,000 | 37,982,010.69432071841439144454 |
| 60,000 | 63,303,351.15720119735731907424 |
| 100,000 | 105,505,585.2620019955955317904 |
About BTU/hour (BTU/h)
BTU per hour (BTU/h) is the standard power unit for heating and cooling equipment in the United States — air conditioners, furnaces, heat pumps, and water heaters are all rated in BTU/hour. One BTU/h equals approximately 0.293 watts. A typical window air conditioner is rated at 5,000–24,000 BTU/h; a central HVAC system for a mid-sized home at 36,000–60,000 BTU/h (called "3 to 5 tons"). The unit appears exclusively in US thermal and HVAC engineering.
A 12,000 BTU/h (1-ton) air conditioner uses roughly 1,200 W of electricity while removing 3,517 W of heat from the room. A typical US gas furnace is rated 60,000–100,000 BTU/h.
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.
BTU/hour – Frequently Asked Questions
How many BTU/h air conditioner do I need for my room?
The classic rule: 20 BTU/h per square foot. A 300 sq ft bedroom needs about 6,000 BTU/h; a 500 sq ft living room about 10,000 BTU/h. But this varies wildly with sun exposure (+10% for south-facing), ceiling height, insulation quality, number of occupants (+600 BTU per person), and climate zone. A room above a pizza oven in Phoenix needs more than a basement in Seattle. When in doubt, oversize slightly — an undersized unit runs constantly and never reaches setpoint.
What happens if you oversize or undersize your home AC unit by a ton?
Undersizing is obvious — the unit runs constantly and never reaches the thermostat setpoint on hot days. But oversizing is worse in subtle ways. An oversized AC cools the air quickly then shuts off before removing enough humidity, leaving you with a clammy 72°F house. The short cycles also wear the compressor faster (startup is the hardest moment) and waste energy. A 1-ton oversize in a humid climate like Florida can raise indoor humidity from a comfortable 45% to a muggy 60%. Proper Manual J load calculations matter more than most homeowners realize.
What does "1 ton" of air conditioning mean in BTU/h?
Exactly 12,000 BTU/h. One ton of AC is the cooling effect of melting one short ton (2,000 lbs) of ice over 24 hours. The ice absorbs 288,000 BTU of heat as it melts (2,000 lbs × 144 BTU/lb latent heat), divided by 24 hours = 12,000 BTU/h. Residential systems run 1.5–5 tons; commercial buildings 10–500 tons. The "ton" unit persists because HVAC contractors think in tons — "that house needs a 3-ton unit" is faster than "that house needs 10.5 kW of cooling."
How efficient is a modern air conditioner in BTU/h per watt?
Modern units achieve 12–25 BTU/h per watt of electricity (SEER 12–25). A SEER 20 unit removes 20 BTU/h of heat for every watt consumed — effectively a 3:1 heat pump ratio. That 12,000 BTU/h window unit draws 500–1,000 W of electricity depending on efficiency. The best mini-splits achieve SEER 30+, removing 30 BTU/h per watt, making them cheaper to run than resistive electric heaters even in heating mode.
How do BTU/h ratings differ between gas furnaces and heat pumps?
A gas furnace's BTU/h rating is its thermal output after combustion efficiency losses (typically 80–96% of fuel input). A heat pump's BTU/h rating is the heat delivered including energy moved from outside — at COP 3, a heat pump delivering 36,000 BTU/h uses only 12,000 BTU/h worth of electricity. This makes direct BTU/h comparisons misleading: a 60,000 BTU/h furnace and a 60,000 BTU/h heat pump deliver the same heat, but the heat pump uses one-third the energy.
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.